[RESEND,v7,03/10] mm: thp: Introduce per-size thp sysfs interface
Commit Message
In preparation for adding support for anonymous small-sized THP,
introduce new sysfs structure that will be used to control the new
behaviours. A new directory is added under transparent_hugepage for each
supported THP size, and contains an `enabled` file, which can be set to
"global" (to inherrit the global setting), "always", "madvise" or
"never". For now, the kernel still only supports PMD-sized anonymous
THP, so only 1 directory is populated.
The first half of the change converts transhuge_vma_suitable() and
hugepage_vma_check() so that they take a bitfield of orders for which
the user wants to determine support, and the functions filter out all
the orders that can't be supported, given the current sysfs
configuration and the VMA dimensions. If there is only 1 order set in
the input then the output can continue to be treated like a boolean;
this is the case for most call sites.
The second half of the change implements the new sysfs interface. It has
been done so that each supported THP size has a `struct thpsize`, which
describes the relevant metadata and is itself a kobject. This is pretty
minimal for now, but should make it easy to add new per-thpsize files to
the interface if needed in future (e.g. per-size defrag). Rather than
keep the `enabled` state directly in the struct thpsize, I've elected to
directly encode it into huge_anon_orders_[always|madvise|global]
bitfields since this reduces the amount of work required in
transhuge_vma_suitable() which is called for every page fault.
The remainder is copied from Documentation/admin-guide/mm/transhuge.rst,
as modified by this commit. See that file for further details.
Transparent Hugepage Support for anonymous memory can be entirely
disabled (mostly for debugging purposes) or only enabled inside
MADV_HUGEPAGE regions (to avoid the risk of consuming more memory
resources) or enabled system wide. This can be achieved
per-supported-THP-size with one of::
echo always >/sys/kernel/mm/transparent_hugepage/hugepages-<size>kB/enabled
echo madvise >/sys/kernel/mm/transparent_hugepage/hugepages-<size>kB/enabled
echo never >/sys/kernel/mm/transparent_hugepage/hugepages-<size>kB/enabled
where <size> is the hugepage size being addressed, the available sizes
for which vary by system. Alternatively it is possible to specify that
a given hugepage size will inherrit the global enabled setting::
echo global >/sys/kernel/mm/transparent_hugepage/hugepages-<size>kB/enabled
The global (legacy) enabled setting can be set as follows::
echo always >/sys/kernel/mm/transparent_hugepage/enabled
echo madvise >/sys/kernel/mm/transparent_hugepage/enabled
echo never >/sys/kernel/mm/transparent_hugepage/enabled
By default, PMD-sized hugepages have enabled="global" and all other
hugepage sizes have enabled="never". If enabling multiple hugepage
sizes, the kernel will select the most appropriate enabled size for a
given allocation.
Signed-off-by: Ryan Roberts <ryan.roberts@arm.com>
---
Documentation/admin-guide/mm/transhuge.rst | 74 ++++--
Documentation/filesystems/proc.rst | 6 +-
fs/proc/task_mmu.c | 3 +-
include/linux/huge_mm.h | 100 +++++---
mm/huge_memory.c | 263 +++++++++++++++++++--
mm/khugepaged.c | 16 +-
mm/memory.c | 6 +-
mm/page_vma_mapped.c | 3 +-
8 files changed, 387 insertions(+), 84 deletions(-)
--
2.25.1
Comments
On 11/22/23 08:29, Ryan Roberts wrote:
> In preparation for adding support for anonymous small-sized THP,
> introduce new sysfs structure that will be used to control the new
> behaviours. A new directory is added under transparent_hugepage for each
> supported THP size, and contains an `enabled` file, which can be set to
> "global" (to inherrit the global setting), "always", "madvise" or
> "never". For now, the kernel still only supports PMD-sized anonymous
> THP, so only 1 directory is populated.
>
> The first half of the change converts transhuge_vma_suitable() and
> hugepage_vma_check() so that they take a bitfield of orders for which
> the user wants to determine support, and the functions filter out all
> the orders that can't be supported, given the current sysfs
> configuration and the VMA dimensions. If there is only 1 order set in
> the input then the output can continue to be treated like a boolean;
> this is the case for most call sites.
>
> The second half of the change implements the new sysfs interface. It has
> been done so that each supported THP size has a `struct thpsize`, which
> describes the relevant metadata and is itself a kobject. This is pretty
> minimal for now, but should make it easy to add new per-thpsize files to
> the interface if needed in future (e.g. per-size defrag). Rather than
> keep the `enabled` state directly in the struct thpsize, I've elected to
> directly encode it into huge_anon_orders_[always|madvise|global]
> bitfields since this reduces the amount of work required in
> transhuge_vma_suitable() which is called for every page fault.
>
> The remainder is copied from Documentation/admin-guide/mm/transhuge.rst,
> as modified by this commit. See that file for further details.
>
> Transparent Hugepage Support for anonymous memory can be entirely
> disabled (mostly for debugging purposes) or only enabled inside
> MADV_HUGEPAGE regions (to avoid the risk of consuming more memory
> resources) or enabled system wide. This can be achieved
> per-supported-THP-size with one of::
>
> echo always >/sys/kernel/mm/transparent_hugepage/hugepages-<size>kB/enabled
> echo madvise >/sys/kernel/mm/transparent_hugepage/hugepages-<size>kB/enabled
> echo never >/sys/kernel/mm/transparent_hugepage/hugepages-<size>kB/enabled
>
> where <size> is the hugepage size being addressed, the available sizes
> for which vary by system. Alternatively it is possible to specify that
> a given hugepage size will inherrit the global enabled setting::
>
> echo global >/sys/kernel/mm/transparent_hugepage/hugepages-<size>kB/enabled
>
> The global (legacy) enabled setting can be set as follows::
>
> echo always >/sys/kernel/mm/transparent_hugepage/enabled
> echo madvise >/sys/kernel/mm/transparent_hugepage/enabled
> echo never >/sys/kernel/mm/transparent_hugepage/enabled
>
> By default, PMD-sized hugepages have enabled="global" and all other
> hugepage sizes have enabled="never". If enabling multiple hugepage
> sizes, the kernel will select the most appropriate enabled size for a
> given allocation.
>
> Signed-off-by: Ryan Roberts <ryan.roberts@arm.com>
> ---
> Documentation/admin-guide/mm/transhuge.rst | 74 ++++--
> Documentation/filesystems/proc.rst | 6 +-
> fs/proc/task_mmu.c | 3 +-
> include/linux/huge_mm.h | 100 +++++---
> mm/huge_memory.c | 263 +++++++++++++++++++--
> mm/khugepaged.c | 16 +-
> mm/memory.c | 6 +-
> mm/page_vma_mapped.c | 3 +-
> 8 files changed, 387 insertions(+), 84 deletions(-)
>
> diff --git a/Documentation/admin-guide/mm/transhuge.rst b/Documentation/admin-guide/mm/transhuge.rst
> index b0cc8243e093..52565e0bd074 100644
> --- a/Documentation/admin-guide/mm/transhuge.rst
> +++ b/Documentation/admin-guide/mm/transhuge.rst
> @@ -45,10 +45,23 @@ components:
> the two is using hugepages just because of the fact the TLB miss is
> going to run faster.
>
> +As well as PMD-sized THP described above, it is also possible to
> +configure the system to allocate "small-sized THP" to back anonymous
Here's one of the places to change to the new name, which lately is
"multi-size THP", or mTHP or m_thp for short. (I've typed "multi-size"
instead of "multi-sized", because the 'd' doesn't add significantly to
the meaning, and if in doubt, shorter is better.
> +memory (for example 16K, 32K, 64K, etc). These THPs continue to be
> +PTE-mapped, but in many cases can still provide similar benefits to
> +those outlined above: Page faults are significantly reduced (by a
> +factor of e.g. 4, 8, 16, etc), but latency spikes are much less
> +prominent because the size of each page isn't as huge as the PMD-sized
> +variant and there is less memory to clear in each page fault. Some
> +architectures also employ TLB compression mechanisms to squeeze more
> +entries in when a set of PTEs are virtually and physically contiguous
> +and approporiately aligned. In this case, TLB misses will occur less
> +often.
> +
OK, all of the above still seems like it can remain the same.
> THP can be enabled system wide or restricted to certain tasks or even
> memory ranges inside task's address space. Unless THP is completely
> disabled, there is ``khugepaged`` daemon that scans memory and
> -collapses sequences of basic pages into huge pages.
> +collapses sequences of basic pages into PMD-sized huge pages.
>
> The THP behaviour is controlled via :ref:`sysfs <thp_sysfs>`
> interface and using madvise(2) and prctl(2) system calls.
> @@ -95,12 +108,29 @@ Global THP controls
> Transparent Hugepage Support for anonymous memory can be entirely disabled
> (mostly for debugging purposes) or only enabled inside MADV_HUGEPAGE
> regions (to avoid the risk of consuming more memory resources) or enabled
> -system wide. This can be achieved with one of::
> +system wide. This can be achieved per-supported-THP-size with one of::
> +
> + echo always >/sys/kernel/mm/transparent_hugepage/hugepages-<size>kB/enabled
> + echo madvise >/sys/kernel/mm/transparent_hugepage/hugepages-<size>kB/enabled
> + echo never >/sys/kernel/mm/transparent_hugepage/hugepages-<size>kB/enabled
> +
> +where <size> is the hugepage size being addressed, the available sizes
> +for which vary by system. Alternatively it is possible to specify that
> +a given hugepage size will inherrit the global enabled setting::
typo: inherrit
> +
> + echo global >/sys/kernel/mm/transparent_hugepage/hugepages-<size>kB/enabled
> +
> +The global (legacy) enabled setting can be set as follows::
>
> echo always >/sys/kernel/mm/transparent_hugepage/enabled
> echo madvise >/sys/kernel/mm/transparent_hugepage/enabled
> echo never >/sys/kernel/mm/transparent_hugepage/enabled
>
> +By default, PMD-sized hugepages have enabled="global" and all other
> +hugepage sizes have enabled="never". If enabling multiple hugepage
> +sizes, the kernel will select the most appropriate enabled size for a
> +given allocation.
> +
This is slightly murky. I wonder if "inherited" is a little more directly
informative than global; it certainly felt that way my first time running
this and poking at it.
And a few trivial examples would be a nice touch.
And so overall with a few other minor tweaks, I'd suggest this:
...
where <size> is the hugepage size being addressed, the available sizes
for which vary by system.
For example:
echo always >/sys/kernel/mm/transparent_hugepage/hugepages-2048kB/enabled
Alternatively it is possible to specify that a given hugepage size will inherit
the top-level "enabled" value:
echo inherited >/sys/kernel/mm/transparent_hugepage/hugepages-<size>kB/enabled
For example:
echo inherited >/sys/kernel/mm/transparent_hugepage/hugepages-2048kB/enabled
The top-level setting (for use with "inherited") can be by issuing one of the
following commands::
echo always >/sys/kernel/mm/transparent_hugepage/enabled
echo madvise >/sys/kernel/mm/transparent_hugepage/enabled
echo never >/sys/kernel/mm/transparent_hugepage/enabled
By default, PMD-sized hugepages have enabled="inherited" and all other
hugepage sizes have enabled="never".
> It's also possible to limit defrag efforts in the VM to generate
> anonymous hugepages in case they're not immediately free to madvise
> regions or to never try to defrag memory and simply fallback to regular
> @@ -146,25 +176,34 @@ madvise
> never
> should be self-explanatory.
>
> -By default kernel tries to use huge zero page on read page fault to
> -anonymous mapping. It's possible to disable huge zero page by writing 0
> -or enable it back by writing 1::
> +By default kernel tries to use huge, PMD-mappable zero page on read
> +page fault to anonymous mapping. It's possible to disable huge zero
> +page by writing 0 or enable it back by writing 1::
>
> echo 0 >/sys/kernel/mm/transparent_hugepage/use_zero_page
> echo 1 >/sys/kernel/mm/transparent_hugepage/use_zero_page
>
> -Some userspace (such as a test program, or an optimized memory allocation
> -library) may want to know the size (in bytes) of a transparent hugepage::
> +Some userspace (such as a test program, or an optimized memory
> +allocation library) may want to know the size (in bytes) of a
> +PMD-mappable transparent hugepage::
>
> cat /sys/kernel/mm/transparent_hugepage/hpage_pmd_size
>
> -khugepaged will be automatically started when
> -transparent_hugepage/enabled is set to "always" or "madvise, and it'll
> -be automatically shutdown if it's set to "never".
> +khugepaged will be automatically started when one or more hugepage
> +sizes are enabled (either by directly setting "always" or "madvise",
> +or by setting "global" while the global enabled is set to "always" or
> +"madvise"), and it'll be automatically shutdown when the last hugepage
> +size is disabled (either by directly setting "never", or by setting
> +"global" while the global enabled is set to "never").
>
> Khugepaged controls
> -------------------
>
> +.. note::
> + khugepaged currently only searches for opportunities to collapse to
> + PMD-sized THP and no attempt is made to collapse to small-sized
> + THP.
> +
> khugepaged runs usually at low frequency so while one may not want to
> invoke defrag algorithms synchronously during the page faults, it
> should be worth invoking defrag at least in khugepaged. However it's
> @@ -282,10 +321,11 @@ force
> Need of application restart
> ===========================
>
> -The transparent_hugepage/enabled values and tmpfs mount option only affect
> -future behavior. So to make them effective you need to restart any
> -application that could have been using hugepages. This also applies to the
> -regions registered in khugepaged.
> +The transparent_hugepage/enabled and
> +transparent_hugepage/hugepages-<size>kB/enabled values and tmpfs mount
> +option only affect future behavior. So to make them effective you need
> +to restart any application that could have been using hugepages. This
> +also applies to the regions registered in khugepaged.
>
> Monitoring usage
> ================
> @@ -308,6 +348,10 @@ frequently will incur overhead.
> There are a number of counters in ``/proc/vmstat`` that may be used to
> monitor how successfully the system is providing huge pages for use.
>
> +.. note::
> + Currently the below counters only record events relating to
> + PMD-sized THP. Events relating to small-sized THP are not included.
Here's another spot to rename to "multi-size THP".
> +
> thp_fault_alloc
> is incremented every time a huge page is successfully
> allocated to handle a page fault.
> @@ -413,7 +457,7 @@ for huge pages.
> Optimizing the applications
> ===========================
>
> -To be guaranteed that the kernel will map a 2M page immediately in any
> +To be guaranteed that the kernel will map a THP immediately in any
> memory region, the mmap region has to be hugepage naturally
> aligned. posix_memalign() can provide that guarantee.
>
> diff --git a/Documentation/filesystems/proc.rst b/Documentation/filesystems/proc.rst
> index 49ef12df631b..f8e8dd1fd148 100644
> --- a/Documentation/filesystems/proc.rst
> +++ b/Documentation/filesystems/proc.rst
> @@ -528,9 +528,9 @@ replaced by copy-on-write) part of the underlying shmem object out on swap.
> does not take into account swapped out page of underlying shmem objects.
> "Locked" indicates whether the mapping is locked in memory or not.
>
> -"THPeligible" indicates whether the mapping is eligible for allocating THP
> -pages as well as the THP is PMD mappable or not - 1 if true, 0 otherwise.
> -It just shows the current status.
> +"THPeligible" indicates whether the mapping is eligible for allocating
> +naturally aligned THP pages of any currently enabled size. 1 if true, 0
> +otherwise. It just shows the current status.
"It just shows the current status"...as opposed to what? I'm missing an
educational opportunity here--not sure what this means. :)
>
> "VmFlags" field deserves a separate description. This member represents the
> kernel flags associated with the particular virtual memory area in two letter
> diff --git a/fs/proc/task_mmu.c b/fs/proc/task_mmu.c
> index 51e0ec658457..2e25362ca9fa 100644
> --- a/fs/proc/task_mmu.c
> +++ b/fs/proc/task_mmu.c
> @@ -865,7 +865,8 @@ static int show_smap(struct seq_file *m, void *v)
> __show_smap(m, &mss, false);
>
> seq_printf(m, "THPeligible: %8u\n",
> - hugepage_vma_check(vma, vma->vm_flags, true, false, true));
> + !!hugepage_vma_check(vma, vma->vm_flags, true, false, true,
> + THP_ORDERS_ALL));
>
> if (arch_pkeys_enabled())
> seq_printf(m, "ProtectionKey: %8u\n", vma_pkey(vma));
> diff --git a/include/linux/huge_mm.h b/include/linux/huge_mm.h
> index fa0350b0812a..7d6f7d96b039 100644
> --- a/include/linux/huge_mm.h
> +++ b/include/linux/huge_mm.h
> @@ -67,6 +67,21 @@ extern struct kobj_attribute shmem_enabled_attr;
> #define HPAGE_PMD_ORDER (HPAGE_PMD_SHIFT-PAGE_SHIFT)
> #define HPAGE_PMD_NR (1<<HPAGE_PMD_ORDER)
>
> +/*
> + * Mask of all large folio orders supported for anonymous THP.
> + */
> +#define THP_ORDERS_ALL_ANON BIT(PMD_ORDER)
> +
> +/*
> + * Mask of all large folio orders supported for file THP.
> + */
> +#define THP_ORDERS_ALL_FILE (BIT(PMD_ORDER) | BIT(PUD_ORDER))
Is there something about file THP that implies PUD_ORDER? This
deserves an explanatory comment, I think.
> +
> +/*
> + * Mask of all large folio orders supported for THP.
> + */
> +#define THP_ORDERS_ALL (THP_ORDERS_ALL_ANON | THP_ORDERS_ALL_FILE)
> +
> #ifdef CONFIG_TRANSPARENT_HUGEPAGE
> #define HPAGE_PMD_SHIFT PMD_SHIFT
> #define HPAGE_PMD_SIZE ((1UL) << HPAGE_PMD_SHIFT)
> @@ -78,13 +93,18 @@ extern struct kobj_attribute shmem_enabled_attr;
>
> extern unsigned long transparent_hugepage_flags;
>
> -#define hugepage_flags_enabled() \
> - (transparent_hugepage_flags & \
> - ((1<<TRANSPARENT_HUGEPAGE_FLAG) | \
> - (1<<TRANSPARENT_HUGEPAGE_REQ_MADV_FLAG)))
> -#define hugepage_flags_always() \
> - (transparent_hugepage_flags & \
> - (1<<TRANSPARENT_HUGEPAGE_FLAG))
Are macros actually required? If not, static inlines would be nicer.
> +bool hugepage_flags_enabled(void);
> +
> +static inline int first_order(unsigned long orders)
> +{
> + return fls_long(orders) - 1;
> +}
> +
> +static inline int next_order(unsigned long *orders, int prev)
> +{
> + *orders &= ~BIT(prev);
> + return first_order(*orders);
> +}
>
> /*
> * Do the below checks:
> @@ -97,23 +117,39 @@ extern unsigned long transparent_hugepage_flags;
> * - For all vmas, check if the haddr is in an aligned HPAGE_PMD_SIZE
> * area.
> */
> -static inline bool transhuge_vma_suitable(struct vm_area_struct *vma,
> - unsigned long addr)
> -{
> - unsigned long haddr;
> -
> - /* Don't have to check pgoff for anonymous vma */
> - if (!vma_is_anonymous(vma)) {
> - if (!IS_ALIGNED((vma->vm_start >> PAGE_SHIFT) - vma->vm_pgoff,
> - HPAGE_PMD_NR))
> - return false;
> +static inline unsigned long transhuge_vma_suitable(struct vm_area_struct *vma,
> + unsigned long addr, unsigned long orders)
Changing this from a bool to a mask of orders is quite significant, and
both the function name and the function-level comment documentation need
to also be adjusted. Here, perhaps one of these names would work:
transhuge_vma_suitable_orders()
transhuge_vma_orders()
> +{
> + int order;
> +
> + /*
> + * Iterate over orders, highest to lowest, removing orders that don't
> + * meet alignment requirements from the set. Exit loop at first order
> + * that meets requirements, since all lower orders must also meet
> + * requirements.
Should we add a little note here, to the effect of, "this is unilaterally
taking over a certain amount of allocation-like policy, by deciding how
to search for folios of a certain size"?
Or is this The Only Way To Do It, after all? I know we had some discussion
about it, and intuitively it feels reasonable, but wanted to poke at it
one last time anyway.
> + */
> +
> + order = first_order(orders);
> +
> + while (orders) {
> + unsigned long hpage_size = PAGE_SIZE << order;
> + unsigned long haddr = ALIGN_DOWN(addr, hpage_size);
> +
> + if (haddr >= vma->vm_start &&
> + haddr + hpage_size <= vma->vm_end) {
> + if (!vma_is_anonymous(vma)) {
> + if (IS_ALIGNED((vma->vm_start >> PAGE_SHIFT) -
> + vma->vm_pgoff,
> + hpage_size >> PAGE_SHIFT))
> + break;
> + } else
> + break;
> + }
> +
> + order = next_order(&orders, order);
> }
>
> - haddr = addr & HPAGE_PMD_MASK;
> -
> - if (haddr < vma->vm_start || haddr + HPAGE_PMD_SIZE > vma->vm_end)
> - return false;
> - return true;
> + return orders;
> }
>
> static inline bool file_thp_enabled(struct vm_area_struct *vma)
> @@ -130,8 +166,9 @@ static inline bool file_thp_enabled(struct vm_area_struct *vma)
> !inode_is_open_for_write(inode) && S_ISREG(inode->i_mode);
> }
>
> -bool hugepage_vma_check(struct vm_area_struct *vma, unsigned long vm_flags,
> - bool smaps, bool in_pf, bool enforce_sysfs);
> +unsigned long hugepage_vma_check(struct vm_area_struct *vma,
> + unsigned long vm_flags, bool smaps, bool in_pf,
> + bool enforce_sysfs, unsigned long orders);
>
> #define transparent_hugepage_use_zero_page() \
> (transparent_hugepage_flags & \
> @@ -267,17 +304,18 @@ static inline bool folio_test_pmd_mappable(struct folio *folio)
> return false;
> }
>
> -static inline bool transhuge_vma_suitable(struct vm_area_struct *vma,
> - unsigned long addr)
> +static inline unsigned long transhuge_vma_suitable(struct vm_area_struct *vma,
> + unsigned long addr, unsigned long orders)
> {
> - return false;
> + return 0;
> }
>
> -static inline bool hugepage_vma_check(struct vm_area_struct *vma,
> - unsigned long vm_flags, bool smaps,
> - bool in_pf, bool enforce_sysfs)
> +static inline unsigned long hugepage_vma_check(struct vm_area_struct *vma,
> + unsigned long vm_flags, bool smaps,
> + bool in_pf, bool enforce_sysfs,
> + unsigned long orders)
> {
> - return false;
> + return 0;
> }
>
> static inline void folio_prep_large_rmappable(struct folio *folio) {}
> diff --git a/mm/huge_memory.c b/mm/huge_memory.c
> index 6eb55f97a3d2..0b545d56420c 100644
> --- a/mm/huge_memory.c
> +++ b/mm/huge_memory.c
> @@ -74,12 +74,60 @@ static unsigned long deferred_split_scan(struct shrinker *shrink,
> static atomic_t huge_zero_refcount;
> struct page *huge_zero_page __read_mostly;
> unsigned long huge_zero_pfn __read_mostly = ~0UL;
> +static unsigned long huge_anon_orders_always __read_mostly;
> +static unsigned long huge_anon_orders_madvise __read_mostly;
> +static unsigned long huge_anon_orders_global __read_mostly;
>
> -bool hugepage_vma_check(struct vm_area_struct *vma, unsigned long vm_flags,
> - bool smaps, bool in_pf, bool enforce_sysfs)
> +#define hugepage_global_enabled() \
> + (transparent_hugepage_flags & \
> + ((1<<TRANSPARENT_HUGEPAGE_FLAG) | \
> + (1<<TRANSPARENT_HUGEPAGE_REQ_MADV_FLAG)))
> +
> +#define hugepage_global_always() \
> + (transparent_hugepage_flags & \
> + (1<<TRANSPARENT_HUGEPAGE_FLAG))
> +
Here again, I'd like to request that we avoid macros, as I don't think
they are strictly required.
> +bool hugepage_flags_enabled(void)
> {
> + /*
> + * We cover both the anon and the file-backed case here; we must return
> + * true if globally enabled, even when all anon sizes are set to never.
> + * So we don't need to look at huge_anon_orders_global.
> + */
> + return hugepage_global_enabled() ||
> + huge_anon_orders_always ||
> + huge_anon_orders_madvise;
> +}
> +
> +/**
> + * hugepage_vma_check - determine which hugepage orders can be applied to vma
> + * @vma: the vm area to check
> + * @vm_flags: use these vm_flags instead of vma->vm_flags
> + * @smaps: whether answer will be used for smaps file
> + * @in_pf: whether answer will be used by page fault handler
> + * @enforce_sysfs: whether sysfs config should be taken into account
> + * @orders: bitfield of all orders to consider
> + *
> + * Calculates the intersection of the requested hugepage orders and the allowed
> + * hugepage orders for the provided vma. Permitted orders are encoded as a set
> + * bit at the corresponding bit position (bit-2 corresponds to order-2, bit-3
> + * corresponds to order-3, etc). Order-0 is never considered a hugepage order.
> + *
> + * Return: bitfield of orders allowed for hugepage in the vma. 0 if no hugepage
> + * orders are allowed.
> + */
> +unsigned long hugepage_vma_check(struct vm_area_struct *vma,
> + unsigned long vm_flags, bool smaps, bool in_pf,
> + bool enforce_sysfs, unsigned long orders)
Here again, a bool return type has been changed to a bitfield. Let's
also update the function name. Maybe one of these:
hugepage_vma_orders()
hugepage_vma_allowable_orders()
?
thanks,
On 29.11.23 04:42, John Hubbard wrote:
> On 11/22/23 08:29, Ryan Roberts wrote:
>> In preparation for adding support for anonymous small-sized THP,
>> introduce new sysfs structure that will be used to control the new
>> behaviours. A new directory is added under transparent_hugepage for each
>> supported THP size, and contains an `enabled` file, which can be set to
>> "global" (to inherrit the global setting), "always", "madvise" or
>> "never". For now, the kernel still only supports PMD-sized anonymous
>> THP, so only 1 directory is populated.
>>
>> The first half of the change converts transhuge_vma_suitable() and
>> hugepage_vma_check() so that they take a bitfield of orders for which
>> the user wants to determine support, and the functions filter out all
>> the orders that can't be supported, given the current sysfs
>> configuration and the VMA dimensions. If there is only 1 order set in
>> the input then the output can continue to be treated like a boolean;
>> this is the case for most call sites.
>>
>> The second half of the change implements the new sysfs interface. It has
>> been done so that each supported THP size has a `struct thpsize`, which
>> describes the relevant metadata and is itself a kobject. This is pretty
>> minimal for now, but should make it easy to add new per-thpsize files to
>> the interface if needed in future (e.g. per-size defrag). Rather than
>> keep the `enabled` state directly in the struct thpsize, I've elected to
>> directly encode it into huge_anon_orders_[always|madvise|global]
>> bitfields since this reduces the amount of work required in
>> transhuge_vma_suitable() which is called for every page fault.
>>
>> The remainder is copied from Documentation/admin-guide/mm/transhuge.rst,
>> as modified by this commit. See that file for further details.
>>
>> Transparent Hugepage Support for anonymous memory can be entirely
>> disabled (mostly for debugging purposes) or only enabled inside
>> MADV_HUGEPAGE regions (to avoid the risk of consuming more memory
>> resources) or enabled system wide. This can be achieved
>> per-supported-THP-size with one of::
>>
>> echo always >/sys/kernel/mm/transparent_hugepage/hugepages-<size>kB/enabled
>> echo madvise >/sys/kernel/mm/transparent_hugepage/hugepages-<size>kB/enabled
>> echo never >/sys/kernel/mm/transparent_hugepage/hugepages-<size>kB/enabled
>>
>> where <size> is the hugepage size being addressed, the available sizes
>> for which vary by system. Alternatively it is possible to specify that
>> a given hugepage size will inherrit the global enabled setting::
>>
>> echo global >/sys/kernel/mm/transparent_hugepage/hugepages-<size>kB/enabled
>>
>> The global (legacy) enabled setting can be set as follows::
>>
>> echo always >/sys/kernel/mm/transparent_hugepage/enabled
>> echo madvise >/sys/kernel/mm/transparent_hugepage/enabled
>> echo never >/sys/kernel/mm/transparent_hugepage/enabled
>>
>> By default, PMD-sized hugepages have enabled="global" and all other
>> hugepage sizes have enabled="never". If enabling multiple hugepage
>> sizes, the kernel will select the most appropriate enabled size for a
>> given allocation.
>>
>> Signed-off-by: Ryan Roberts <ryan.roberts@arm.com>
>> ---
>> Documentation/admin-guide/mm/transhuge.rst | 74 ++++--
>> Documentation/filesystems/proc.rst | 6 +-
>> fs/proc/task_mmu.c | 3 +-
>> include/linux/huge_mm.h | 100 +++++---
>> mm/huge_memory.c | 263 +++++++++++++++++++--
>> mm/khugepaged.c | 16 +-
>> mm/memory.c | 6 +-
>> mm/page_vma_mapped.c | 3 +-
>> 8 files changed, 387 insertions(+), 84 deletions(-)
>>
>> diff --git a/Documentation/admin-guide/mm/transhuge.rst b/Documentation/admin-guide/mm/transhuge.rst
>> index b0cc8243e093..52565e0bd074 100644
>> --- a/Documentation/admin-guide/mm/transhuge.rst
>> +++ b/Documentation/admin-guide/mm/transhuge.rst
>> @@ -45,10 +45,23 @@ components:
>> the two is using hugepages just because of the fact the TLB miss is
>> going to run faster.
>>
>> +As well as PMD-sized THP described above, it is also possible to
>> +configure the system to allocate "small-sized THP" to back anonymous
>
> Here's one of the places to change to the new name, which lately is
> "multi-size THP", or mTHP or m_thp for short. (I've typed "multi-size"
> instead of "multi-sized", because the 'd' doesn't add significantly to
> the meaning, and if in doubt, shorter is better.
>
>
>> +memory (for example 16K, 32K, 64K, etc). These THPs continue to be
>> +PTE-mapped, but in many cases can still provide similar benefits to
>> +those outlined above: Page faults are significantly reduced (by a
>> +factor of e.g. 4, 8, 16, etc), but latency spikes are much less
>> +prominent because the size of each page isn't as huge as the PMD-sized
>> +variant and there is less memory to clear in each page fault. Some
>> +architectures also employ TLB compression mechanisms to squeeze more
>> +entries in when a set of PTEs are virtually and physically contiguous
>> +and approporiately aligned. In this case, TLB misses will occur less
>> +often.
>> +
>
> OK, all of the above still seems like it can remain the same.
>
>> THP can be enabled system wide or restricted to certain tasks or even
>> memory ranges inside task's address space. Unless THP is completely
>> disabled, there is ``khugepaged`` daemon that scans memory and
>> -collapses sequences of basic pages into huge pages.
>> +collapses sequences of basic pages into PMD-sized huge pages.
>>
>> The THP behaviour is controlled via :ref:`sysfs <thp_sysfs>`
>> interface and using madvise(2) and prctl(2) system calls.
>> @@ -95,12 +108,29 @@ Global THP controls
>> Transparent Hugepage Support for anonymous memory can be entirely disabled
>> (mostly for debugging purposes) or only enabled inside MADV_HUGEPAGE
>> regions (to avoid the risk of consuming more memory resources) or enabled
>> -system wide. This can be achieved with one of::
>> +system wide. This can be achieved per-supported-THP-size with one of::
>> +
>> + echo always >/sys/kernel/mm/transparent_hugepage/hugepages-<size>kB/enabled
>> + echo madvise >/sys/kernel/mm/transparent_hugepage/hugepages-<size>kB/enabled
>> + echo never >/sys/kernel/mm/transparent_hugepage/hugepages-<size>kB/enabled
>> +
>> +where <size> is the hugepage size being addressed, the available sizes
>> +for which vary by system. Alternatively it is possible to specify that
>> +a given hugepage size will inherrit the global enabled setting::
>
> typo: inherrit
>
>> +
>> + echo global >/sys/kernel/mm/transparent_hugepage/hugepages-<size>kB/enabled
>> +
>> +The global (legacy) enabled setting can be set as follows::
>>
>> echo always >/sys/kernel/mm/transparent_hugepage/enabled
>> echo madvise >/sys/kernel/mm/transparent_hugepage/enabled
>> echo never >/sys/kernel/mm/transparent_hugepage/enabled
>>
>> +By default, PMD-sized hugepages have enabled="global" and all other
>> +hugepage sizes have enabled="never". If enabling multiple hugepage
>> +sizes, the kernel will select the most appropriate enabled size for a
>> +given allocation.
>> +
>
> This is slightly murky. I wonder if "inherited" is a little more directly
> informative than global; it certainly felt that way my first time running
> this and poking at it.
>
> And a few trivial examples would be a nice touch.
>
> And so overall with a few other minor tweaks, I'd suggest this:
>
> ...
> where <size> is the hugepage size being addressed, the available sizes
> for which vary by system.
>
> For example:
> echo always >/sys/kernel/mm/transparent_hugepage/hugepages-2048kB/enabled
>
> Alternatively it is possible to specify that a given hugepage size will inherit
> the top-level "enabled" value:
>
> echo inherited >/sys/kernel/mm/transparent_hugepage/hugepages-<size>kB/enabled
>
> For example:
> echo inherited >/sys/kernel/mm/transparent_hugepage/hugepages-2048kB/enabled
>
> The top-level setting (for use with "inherited") can be by issuing one of the
> following commands::
>
> echo always >/sys/kernel/mm/transparent_hugepage/enabled
> echo madvise >/sys/kernel/mm/transparent_hugepage/enabled
> echo never >/sys/kernel/mm/transparent_hugepage/enabled
>
> By default, PMD-sized hugepages have enabled="inherited" and all other
> hugepage sizes have enabled="never".
"inherited" works for me as well.
On 29/11/2023 03:42, John Hubbard wrote:
> On 11/22/23 08:29, Ryan Roberts wrote:
>> In preparation for adding support for anonymous small-sized THP,
>> introduce new sysfs structure that will be used to control the new
>> behaviours. A new directory is added under transparent_hugepage for each
>> supported THP size, and contains an `enabled` file, which can be set to
>> "global" (to inherrit the global setting), "always", "madvise" or
>> "never". For now, the kernel still only supports PMD-sized anonymous
>> THP, so only 1 directory is populated.
>>
>> The first half of the change converts transhuge_vma_suitable() and
>> hugepage_vma_check() so that they take a bitfield of orders for which
>> the user wants to determine support, and the functions filter out all
>> the orders that can't be supported, given the current sysfs
>> configuration and the VMA dimensions. If there is only 1 order set in
>> the input then the output can continue to be treated like a boolean;
>> this is the case for most call sites.
>>
>> The second half of the change implements the new sysfs interface. It has
>> been done so that each supported THP size has a `struct thpsize`, which
>> describes the relevant metadata and is itself a kobject. This is pretty
>> minimal for now, but should make it easy to add new per-thpsize files to
>> the interface if needed in future (e.g. per-size defrag). Rather than
>> keep the `enabled` state directly in the struct thpsize, I've elected to
>> directly encode it into huge_anon_orders_[always|madvise|global]
>> bitfields since this reduces the amount of work required in
>> transhuge_vma_suitable() which is called for every page fault.
>>
>> The remainder is copied from Documentation/admin-guide/mm/transhuge.rst,
>> as modified by this commit. See that file for further details.
>>
>> Transparent Hugepage Support for anonymous memory can be entirely
>> disabled (mostly for debugging purposes) or only enabled inside
>> MADV_HUGEPAGE regions (to avoid the risk of consuming more memory
>> resources) or enabled system wide. This can be achieved
>> per-supported-THP-size with one of::
>>
>> echo always >/sys/kernel/mm/transparent_hugepage/hugepages-<size>kB/enabled
>> echo madvise >/sys/kernel/mm/transparent_hugepage/hugepages-<size>kB/enabled
>> echo never >/sys/kernel/mm/transparent_hugepage/hugepages-<size>kB/enabled
>>
>> where <size> is the hugepage size being addressed, the available sizes
>> for which vary by system. Alternatively it is possible to specify that
>> a given hugepage size will inherrit the global enabled setting::
>>
>> echo global >/sys/kernel/mm/transparent_hugepage/hugepages-<size>kB/enabled
>>
>> The global (legacy) enabled setting can be set as follows::
>>
>> echo always >/sys/kernel/mm/transparent_hugepage/enabled
>> echo madvise >/sys/kernel/mm/transparent_hugepage/enabled
>> echo never >/sys/kernel/mm/transparent_hugepage/enabled
>>
>> By default, PMD-sized hugepages have enabled="global" and all other
>> hugepage sizes have enabled="never". If enabling multiple hugepage
>> sizes, the kernel will select the most appropriate enabled size for a
>> given allocation.
>>
>> Signed-off-by: Ryan Roberts <ryan.roberts@arm.com>
>> ---
>> Documentation/admin-guide/mm/transhuge.rst | 74 ++++--
>> Documentation/filesystems/proc.rst | 6 +-
>> fs/proc/task_mmu.c | 3 +-
>> include/linux/huge_mm.h | 100 +++++---
>> mm/huge_memory.c | 263 +++++++++++++++++++--
>> mm/khugepaged.c | 16 +-
>> mm/memory.c | 6 +-
>> mm/page_vma_mapped.c | 3 +-
>> 8 files changed, 387 insertions(+), 84 deletions(-)
>>
>> diff --git a/Documentation/admin-guide/mm/transhuge.rst
>> b/Documentation/admin-guide/mm/transhuge.rst
>> index b0cc8243e093..52565e0bd074 100644
>> --- a/Documentation/admin-guide/mm/transhuge.rst
>> +++ b/Documentation/admin-guide/mm/transhuge.rst
>> @@ -45,10 +45,23 @@ components:
>> the two is using hugepages just because of the fact the TLB miss is
>> going to run faster.
>>
>> +As well as PMD-sized THP described above, it is also possible to
>> +configure the system to allocate "small-sized THP" to back anonymous
>
> Here's one of the places to change to the new name, which lately is
> "multi-size THP", or mTHP or m_thp for short. (I've typed "multi-size"
> instead of "multi-sized", because the 'd' doesn't add significantly to
> the meaning, and if in doubt, shorter is better.
I was thinking of some light changes to the start of this paragraph, something like:
Modern kernels support "multi-size THP" (mTHP), which introduces the ability to
allocate memory in blocks that are bigger than a base page but smaller than
traditional PMD-size (as described above, in increments of a power-of-2 number
of pages. mTHP can back anonymous
>
>
>> +memory (for example 16K, 32K, 64K, etc). These THPs continue to be
>> +PTE-mapped, but in many cases can still provide similar benefits to
>> +those outlined above: Page faults are significantly reduced (by a
>> +factor of e.g. 4, 8, 16, etc), but latency spikes are much less
>> +prominent because the size of each page isn't as huge as the PMD-sized
>> +variant and there is less memory to clear in each page fault. Some
>> +architectures also employ TLB compression mechanisms to squeeze more
>> +entries in when a set of PTEs are virtually and physically contiguous
>> +and approporiately aligned. In this case, TLB misses will occur less
>> +often.
>> +
>
> OK, all of the above still seems like it can remain the same.
>
>> THP can be enabled system wide or restricted to certain tasks or even
>> memory ranges inside task's address space. Unless THP is completely
>> disabled, there is ``khugepaged`` daemon that scans memory and
>> -collapses sequences of basic pages into huge pages.
>> +collapses sequences of basic pages into PMD-sized huge pages.
>>
>> The THP behaviour is controlled via :ref:`sysfs <thp_sysfs>`
>> interface and using madvise(2) and prctl(2) system calls.
>> @@ -95,12 +108,29 @@ Global THP controls
>> Transparent Hugepage Support for anonymous memory can be entirely disabled
>> (mostly for debugging purposes) or only enabled inside MADV_HUGEPAGE
>> regions (to avoid the risk of consuming more memory resources) or enabled
>> -system wide. This can be achieved with one of::
>> +system wide. This can be achieved per-supported-THP-size with one of::
>> +
>> + echo always >/sys/kernel/mm/transparent_hugepage/hugepages-<size>kB/enabled
>> + echo madvise >/sys/kernel/mm/transparent_hugepage/hugepages-<size>kB/enabled
>> + echo never >/sys/kernel/mm/transparent_hugepage/hugepages-<size>kB/enabled
>> +
>> +where <size> is the hugepage size being addressed, the available sizes
>> +for which vary by system. Alternatively it is possible to specify that
>> +a given hugepage size will inherrit the global enabled setting::
>
> typo: inherrit
ACK, will fix
>
>> +
>> + echo global >/sys/kernel/mm/transparent_hugepage/hugepages-<size>kB/enabled
>> +
>> +The global (legacy) enabled setting can be set as follows::
>>
>> echo always >/sys/kernel/mm/transparent_hugepage/enabled
>> echo madvise >/sys/kernel/mm/transparent_hugepage/enabled
>> echo never >/sys/kernel/mm/transparent_hugepage/enabled
>>
>> +By default, PMD-sized hugepages have enabled="global" and all other
>> +hugepage sizes have enabled="never". If enabling multiple hugepage
>> +sizes, the kernel will select the most appropriate enabled size for a
>> +given allocation.
>> +
>
> This is slightly murky. I wonder if "inherited" is a little more directly
> informative than global; it certainly felt that way my first time running
> this and poking at it.
>
> And a few trivial examples would be a nice touch.
>
> And so overall with a few other minor tweaks, I'd suggest this:
>
> ...
> where <size> is the hugepage size being addressed, the available sizes
> for which vary by system.
>
> For example:
> echo always >/sys/kernel/mm/transparent_hugepage/hugepages-2048kB/enabled
>
> Alternatively it is possible to specify that a given hugepage size will inherit
> the top-level "enabled" value:
>
> echo inherited >/sys/kernel/mm/transparent_hugepage/hugepages-<size>kB/enabled
>
> For example:
> echo inherited >/sys/kernel/mm/transparent_hugepage/hugepages-2048kB/enabled
>
> The top-level setting (for use with "inherited") can be by issuing one of the
> following commands::
>
> echo always >/sys/kernel/mm/transparent_hugepage/enabled
> echo madvise >/sys/kernel/mm/transparent_hugepage/enabled
> echo never >/sys/kernel/mm/transparent_hugepage/enabled
>
> By default, PMD-sized hugepages have enabled="inherited" and all other
> hugepage sizes have enabled="never".
That all sounds good; will update.
I wonder if "inherit" is even better than "inherited" though?
>
>
>> It's also possible to limit defrag efforts in the VM to generate
>> anonymous hugepages in case they're not immediately free to madvise
>> regions or to never try to defrag memory and simply fallback to regular
>> @@ -146,25 +176,34 @@ madvise
>> never
>> should be self-explanatory.
>>
>> -By default kernel tries to use huge zero page on read page fault to
>> -anonymous mapping. It's possible to disable huge zero page by writing 0
>> -or enable it back by writing 1::
>> +By default kernel tries to use huge, PMD-mappable zero page on read
>> +page fault to anonymous mapping. It's possible to disable huge zero
>> +page by writing 0 or enable it back by writing 1::
>>
>> echo 0 >/sys/kernel/mm/transparent_hugepage/use_zero_page
>> echo 1 >/sys/kernel/mm/transparent_hugepage/use_zero_page
>>
>> -Some userspace (such as a test program, or an optimized memory allocation
>> -library) may want to know the size (in bytes) of a transparent hugepage::
>> +Some userspace (such as a test program, or an optimized memory
>> +allocation library) may want to know the size (in bytes) of a
>> +PMD-mappable transparent hugepage::
>>
>> cat /sys/kernel/mm/transparent_hugepage/hpage_pmd_size
>>
>> -khugepaged will be automatically started when
>> -transparent_hugepage/enabled is set to "always" or "madvise, and it'll
>> -be automatically shutdown if it's set to "never".
>> +khugepaged will be automatically started when one or more hugepage
>> +sizes are enabled (either by directly setting "always" or "madvise",
>> +or by setting "global" while the global enabled is set to "always" or
>> +"madvise"), and it'll be automatically shutdown when the last hugepage
>> +size is disabled (either by directly setting "never", or by setting
>> +"global" while the global enabled is set to "never").
>>
>> Khugepaged controls
>> -------------------
>>
>> +.. note::
>> + khugepaged currently only searches for opportunities to collapse to
>> + PMD-sized THP and no attempt is made to collapse to small-sized
>> + THP.
>> +
"small-sized THP" used here too; I propose to change it to "... collapse to
other THP sizes."
>> khugepaged runs usually at low frequency so while one may not want to
>> invoke defrag algorithms synchronously during the page faults, it
>> should be worth invoking defrag at least in khugepaged. However it's
>> @@ -282,10 +321,11 @@ force
>> Need of application restart
>> ===========================
>>
>> -The transparent_hugepage/enabled values and tmpfs mount option only affect
>> -future behavior. So to make them effective you need to restart any
>> -application that could have been using hugepages. This also applies to the
>> -regions registered in khugepaged.
>> +The transparent_hugepage/enabled and
>> +transparent_hugepage/hugepages-<size>kB/enabled values and tmpfs mount
>> +option only affect future behavior. So to make them effective you need
>> +to restart any application that could have been using hugepages. This
>> +also applies to the regions registered in khugepaged.
>>
>> Monitoring usage
>> ================
>> @@ -308,6 +348,10 @@ frequently will incur overhead.
>> There are a number of counters in ``/proc/vmstat`` that may be used to
>> monitor how successfully the system is providing huge pages for use.
>>
>> +.. note::
>> + Currently the below counters only record events relating to
>> + PMD-sized THP. Events relating to small-sized THP are not included.
>
> Here's another spot to rename to "multi-size THP".
I propose to change it to "Events relating to other THP sizes..."
I'm also going to move this note to just under the "Monitoring Usage" heading
since its current position doesn't make it clear that it includes
"AnonHugePages". I'll also make it clear in the text that mentions AnonHugePages
counter that it "only applies to traditional PMD-sized THP for historical
reasons" and that "AnonHugePages should have been called AnonHugePmdMapped" as
David suggested in the other thread.
>
>> +
>> thp_fault_alloc
>> is incremented every time a huge page is successfully
>> allocated to handle a page fault.
>> @@ -413,7 +457,7 @@ for huge pages.
>> Optimizing the applications
>> ===========================
>>
>> -To be guaranteed that the kernel will map a 2M page immediately in any
>> +To be guaranteed that the kernel will map a THP immediately in any
>> memory region, the mmap region has to be hugepage naturally
>> aligned. posix_memalign() can provide that guarantee.
>>
>> diff --git a/Documentation/filesystems/proc.rst
>> b/Documentation/filesystems/proc.rst
>> index 49ef12df631b..f8e8dd1fd148 100644
>> --- a/Documentation/filesystems/proc.rst
>> +++ b/Documentation/filesystems/proc.rst
>> @@ -528,9 +528,9 @@ replaced by copy-on-write) part of the underlying shmem
>> object out on swap.
>> does not take into account swapped out page of underlying shmem objects.
>> "Locked" indicates whether the mapping is locked in memory or not.
>>
>> -"THPeligible" indicates whether the mapping is eligible for allocating THP
>> -pages as well as the THP is PMD mappable or not - 1 if true, 0 otherwise.
>> -It just shows the current status.
>> +"THPeligible" indicates whether the mapping is eligible for allocating
>> +naturally aligned THP pages of any currently enabled size. 1 if true, 0
>> +otherwise. It just shows the current status.
>
> "It just shows the current status"...as opposed to what? I'm missing an
> educational opportunity here--not sure what this means. :)
I have no idea either - it seems superfluous. But that sentence was there
already. I can remove it if you like?
>
>>
>> "VmFlags" field deserves a separate description. This member represents the
>> kernel flags associated with the particular virtual memory area in two letter
>> diff --git a/fs/proc/task_mmu.c b/fs/proc/task_mmu.c
>> index 51e0ec658457..2e25362ca9fa 100644
>> --- a/fs/proc/task_mmu.c
>> +++ b/fs/proc/task_mmu.c
>> @@ -865,7 +865,8 @@ static int show_smap(struct seq_file *m, void *v)
>> __show_smap(m, &mss, false);
>>
>> seq_printf(m, "THPeligible: %8u\n",
>> - hugepage_vma_check(vma, vma->vm_flags, true, false, true));
>> + !!hugepage_vma_check(vma, vma->vm_flags, true, false, true,
>> + THP_ORDERS_ALL));
>>
>> if (arch_pkeys_enabled())
>> seq_printf(m, "ProtectionKey: %8u\n", vma_pkey(vma));
>> diff --git a/include/linux/huge_mm.h b/include/linux/huge_mm.h
>> index fa0350b0812a..7d6f7d96b039 100644
>> --- a/include/linux/huge_mm.h
>> +++ b/include/linux/huge_mm.h
>> @@ -67,6 +67,21 @@ extern struct kobj_attribute shmem_enabled_attr;
>> #define HPAGE_PMD_ORDER (HPAGE_PMD_SHIFT-PAGE_SHIFT)
>> #define HPAGE_PMD_NR (1<<HPAGE_PMD_ORDER)
>>
>> +/*
>> + * Mask of all large folio orders supported for anonymous THP.
>> + */
>> +#define THP_ORDERS_ALL_ANON BIT(PMD_ORDER)
>> +
>> +/*
>> + * Mask of all large folio orders supported for file THP.
>> + */
>> +#define THP_ORDERS_ALL_FILE (BIT(PMD_ORDER) | BIT(PUD_ORDER))
>
> Is there something about file THP that implies PUD_ORDER? This
> deserves an explanatory comment, I think.
Sorry, I'm not really sure what you are asking? Today's kernel supports
PUD-mapping file-backed memory (mostly DAX I believe). I'm not sure what comment
you want me to add, other than "file-backed memory can support PUD-mapping", but
that's self-evident from the define, isn't it?
>
>> +
>> +/*
>> + * Mask of all large folio orders supported for THP.
>> + */
>> +#define THP_ORDERS_ALL (THP_ORDERS_ALL_ANON | THP_ORDERS_ALL_FILE)
>> +
>> #ifdef CONFIG_TRANSPARENT_HUGEPAGE
>> #define HPAGE_PMD_SHIFT PMD_SHIFT
>> #define HPAGE_PMD_SIZE ((1UL) << HPAGE_PMD_SHIFT)
>> @@ -78,13 +93,18 @@ extern struct kobj_attribute shmem_enabled_attr;
>>
>> extern unsigned long transparent_hugepage_flags;
>>
>> -#define hugepage_flags_enabled() \
>> - (transparent_hugepage_flags & \
>> - ((1<<TRANSPARENT_HUGEPAGE_FLAG) | \
>> - (1<<TRANSPARENT_HUGEPAGE_REQ_MADV_FLAG)))
>> -#define hugepage_flags_always() \
>> - (transparent_hugepage_flags & \
>> - (1<<TRANSPARENT_HUGEPAGE_FLAG))
>
> Are macros actually required? If not, static inlines would be nicer.
I agree static inlines are nicer. Here I'm removing existing macros though, and
replacing with a function prototype (hugepage_flags_enabled()), which is
implemented in huge_memory.c; this avoids having to export a bunch of global
variables from that file if it were to be static inline.
>
>> +bool hugepage_flags_enabled(void);
>> +
>> +static inline int first_order(unsigned long orders)
>> +{
>> + return fls_long(orders) - 1;
>> +}
>> +
>> +static inline int next_order(unsigned long *orders, int prev)
>> +{
>> + *orders &= ~BIT(prev);
>> + return first_order(*orders);
>> +}
>>
>> /*
>> * Do the below checks:
>> @@ -97,23 +117,39 @@ extern unsigned long transparent_hugepage_flags;
>> * - For all vmas, check if the haddr is in an aligned HPAGE_PMD_SIZE
>> * area.
>> */
>> -static inline bool transhuge_vma_suitable(struct vm_area_struct *vma,
>> - unsigned long addr)
>> -{
>> - unsigned long haddr;
>> -
>> - /* Don't have to check pgoff for anonymous vma */
>> - if (!vma_is_anonymous(vma)) {
>> - if (!IS_ALIGNED((vma->vm_start >> PAGE_SHIFT) - vma->vm_pgoff,
>> - HPAGE_PMD_NR))
>> - return false;
>> +static inline unsigned long transhuge_vma_suitable(struct vm_area_struct *vma,
>> + unsigned long addr, unsigned long orders)
>
> Changing this from a bool to a mask of orders is quite significant, and
> both the function name and the function-level comment documentation need
> to also be adjusted. Here, perhaps one of these names would work:
>
> transhuge_vma_suitable_orders()
This is my preference, but its getting a bit long. How about:
thp_vma_suitable_orders()
I could then call the other one:
thp_vma_allowable_orders()
So we have a clearly related pair?
> transhuge_vma_orders()>
>
>> +{
>> + int order;
>> +
>> + /*
>> + * Iterate over orders, highest to lowest, removing orders that don't
>> + * meet alignment requirements from the set. Exit loop at first order
>> + * that meets requirements, since all lower orders must also meet
>> + * requirements.
>
> Should we add a little note here, to the effect of, "this is unilaterally
> taking over a certain amount of allocation-like policy, by deciding how
> to search for folios of a certain size"?
>
> Or is this The Only Way To Do It, after all? I know we had some discussion
> about it, and intuitively it feels reasonable, but wanted to poke at it
> one last time anyway.
This function isn't trying to implement policy, its just filtering out orders
that don't fit and therefore definitely cannot be used. The result is a set of
orders the could be used and its the policy maker's job to decide which one.
Currently that policy is "biggest one that fits && does not overlap other
non-none ptes && folio successfully allocated". That's implemented in the next
patch and would potentially be swapped out in the future for something more
exotic/optimal.
So I don't think we need any extra comments here.
>
>> + */
>> +
>> + order = first_order(orders);
>> +
>> + while (orders) {
>> + unsigned long hpage_size = PAGE_SIZE << order;
>> + unsigned long haddr = ALIGN_DOWN(addr, hpage_size);
>> +
>> + if (haddr >= vma->vm_start &&
>> + haddr + hpage_size <= vma->vm_end) {
>> + if (!vma_is_anonymous(vma)) {
>> + if (IS_ALIGNED((vma->vm_start >> PAGE_SHIFT) -
>> + vma->vm_pgoff,
>> + hpage_size >> PAGE_SHIFT))
>> + break;
>> + } else
>> + break;
>> + }
>> +
>> + order = next_order(&orders, order);
>> }
>>
>> - haddr = addr & HPAGE_PMD_MASK;
>> -
>> - if (haddr < vma->vm_start || haddr + HPAGE_PMD_SIZE > vma->vm_end)
>> - return false;
>> - return true;
>> + return orders;
>> }
>>
>> static inline bool file_thp_enabled(struct vm_area_struct *vma)
>> @@ -130,8 +166,9 @@ static inline bool file_thp_enabled(struct vm_area_struct
>> *vma)
>> !inode_is_open_for_write(inode) && S_ISREG(inode->i_mode);
>> }
>>
>> -bool hugepage_vma_check(struct vm_area_struct *vma, unsigned long vm_flags,
>> - bool smaps, bool in_pf, bool enforce_sysfs);
>> +unsigned long hugepage_vma_check(struct vm_area_struct *vma,
>> + unsigned long vm_flags, bool smaps, bool in_pf,
>> + bool enforce_sysfs, unsigned long orders);
>>
>> #define transparent_hugepage_use_zero_page() \
>> (transparent_hugepage_flags & \
>> @@ -267,17 +304,18 @@ static inline bool folio_test_pmd_mappable(struct folio
>> *folio)
>> return false;
>> }
>>
>> -static inline bool transhuge_vma_suitable(struct vm_area_struct *vma,
>> - unsigned long addr)
>> +static inline unsigned long transhuge_vma_suitable(struct vm_area_struct *vma,
>> + unsigned long addr, unsigned long orders)
>> {
>> - return false;
>> + return 0;
>> }
>>
>> -static inline bool hugepage_vma_check(struct vm_area_struct *vma,
>> - unsigned long vm_flags, bool smaps,
>> - bool in_pf, bool enforce_sysfs)
>> +static inline unsigned long hugepage_vma_check(struct vm_area_struct *vma,
>> + unsigned long vm_flags, bool smaps,
>> + bool in_pf, bool enforce_sysfs,
>> + unsigned long orders)
>> {
>> - return false;
>> + return 0;
>> }
>>
>> static inline void folio_prep_large_rmappable(struct folio *folio) {}
>> diff --git a/mm/huge_memory.c b/mm/huge_memory.c
>> index 6eb55f97a3d2..0b545d56420c 100644
>> --- a/mm/huge_memory.c
>> +++ b/mm/huge_memory.c
>> @@ -74,12 +74,60 @@ static unsigned long deferred_split_scan(struct shrinker
>> *shrink,
>> static atomic_t huge_zero_refcount;
>> struct page *huge_zero_page __read_mostly;
>> unsigned long huge_zero_pfn __read_mostly = ~0UL;
>> +static unsigned long huge_anon_orders_always __read_mostly;
>> +static unsigned long huge_anon_orders_madvise __read_mostly;
>> +static unsigned long huge_anon_orders_global __read_mostly;
>>
>> -bool hugepage_vma_check(struct vm_area_struct *vma, unsigned long vm_flags,
>> - bool smaps, bool in_pf, bool enforce_sysfs)
>> +#define hugepage_global_enabled() \
>> + (transparent_hugepage_flags & \
>> + ((1<<TRANSPARENT_HUGEPAGE_FLAG) | \
>> + (1<<TRANSPARENT_HUGEPAGE_REQ_MADV_FLAG)))
>> +
>> +#define hugepage_global_always() \
>> + (transparent_hugepage_flags & \
>> + (1<<TRANSPARENT_HUGEPAGE_FLAG))
>> +
>
> Here again, I'd like to request that we avoid macros, as I don't think
> they are strictly required.
Yeah I agree. I did them this way, because they already existed and I was just
moving them from the header to here. But I'll change to static inline.
>
>> +bool hugepage_flags_enabled(void)
>> {
>> + /*
>> + * We cover both the anon and the file-backed case here; we must return
>> + * true if globally enabled, even when all anon sizes are set to never.
>> + * So we don't need to look at huge_anon_orders_global.
>> + */
>> + return hugepage_global_enabled() ||
>> + huge_anon_orders_always ||
>> + huge_anon_orders_madvise;
>> +}
>> +
>> +/**
>> + * hugepage_vma_check - determine which hugepage orders can be applied to vma
>> + * @vma: the vm area to check
>> + * @vm_flags: use these vm_flags instead of vma->vm_flags
>> + * @smaps: whether answer will be used for smaps file
>> + * @in_pf: whether answer will be used by page fault handler
>> + * @enforce_sysfs: whether sysfs config should be taken into account
>> + * @orders: bitfield of all orders to consider
>> + *
>> + * Calculates the intersection of the requested hugepage orders and the allowed
>> + * hugepage orders for the provided vma. Permitted orders are encoded as a set
>> + * bit at the corresponding bit position (bit-2 corresponds to order-2, bit-3
>> + * corresponds to order-3, etc). Order-0 is never considered a hugepage order.
>> + *
>> + * Return: bitfield of orders allowed for hugepage in the vma. 0 if no hugepage
>> + * orders are allowed.
>> + */
>> +unsigned long hugepage_vma_check(struct vm_area_struct *vma,
>> + unsigned long vm_flags, bool smaps, bool in_pf,
>> + bool enforce_sysfs, unsigned long orders)
>
> Here again, a bool return type has been changed to a bitfield. Let's
> also update the function name. Maybe one of these:
>
> hugepage_vma_orders()
> hugepage_vma_allowable_orders()
thp_vma_allowable_orders()?
Thanks for the review!
>
> ?
>
>
> thanks,
1On 11/29/23 03:05, Ryan Roberts wrote:
> On 29/11/2023 03:42, John Hubbard wrote:
>> On 11/22/23 08:29, Ryan Roberts wrote:
...
>>> +As well as PMD-sized THP described above, it is also possible to
>>> +configure the system to allocate "small-sized THP" to back anonymous
>>
>> Here's one of the places to change to the new name, which lately is
>> "multi-size THP", or mTHP or m_thp for short. (I've typed "multi-size"
>> instead of "multi-sized", because the 'd' doesn't add significantly to
>> the meaning, and if in doubt, shorter is better.
>
> I was thinking of some light changes to the start of this paragraph, something like:
>
> Modern kernels support "multi-size THP" (mTHP), which introduces the ability to
> allocate memory in blocks that are bigger than a base page but smaller than
> traditional PMD-size (as described above, in increments of a power-of-2 number
> of pages. mTHP can back anonymous
>
Very nice.
...
>> By default, PMD-sized hugepages have enabled="inherited" and all other
>> hugepage sizes have enabled="never".
>
> That all sounds good; will update.
>
> I wonder if "inherit" is even better than "inherited" though?
Yes, I think so. "inherit" was actually my first idea, and after
thinking about it, I just made it worse by adding the "ed". haha. :)
...
>>> Khugepaged controls
>>> -------------------
>>>
>>> +.. note::
>>> + khugepaged currently only searches for opportunities to collapse to
>>> + PMD-sized THP and no attempt is made to collapse to small-sized
>>> + THP.
>>> +
>
> "small-sized THP" used here too; I propose to change it to "... collapse to
> other THP sizes."
OK, looks good.
>
>>> khugepaged runs usually at low frequency so while one may not want to
>>> invoke defrag algorithms synchronously during the page faults, it
>>> should be worth invoking defrag at least in khugepaged. However it's
>>> @@ -282,10 +321,11 @@ force
>>> Need of application restart
>>> ===========================
>>>
>>> -The transparent_hugepage/enabled values and tmpfs mount option only affect
>>> -future behavior. So to make them effective you need to restart any
>>> -application that could have been using hugepages. This also applies to the
>>> -regions registered in khugepaged.
>>> +The transparent_hugepage/enabled and
>>> +transparent_hugepage/hugepages-<size>kB/enabled values and tmpfs mount
>>> +option only affect future behavior. So to make them effective you need
>>> +to restart any application that could have been using hugepages. This
>>> +also applies to the regions registered in khugepaged.
>>>
>>> Monitoring usage
>>> ================
>>> @@ -308,6 +348,10 @@ frequently will incur overhead.
>>> There are a number of counters in ``/proc/vmstat`` that may be used to
>>> monitor how successfully the system is providing huge pages for use.
>>>
>>> +.. note::
>>> + Currently the below counters only record events relating to
>>> + PMD-sized THP. Events relating to small-sized THP are not included.
>>
>> Here's another spot to rename to "multi-size THP".
>
> I propose to change it to "Events relating to other THP sizes..."
>
> I'm also going to move this note to just under the "Monitoring Usage" heading
> since its current position doesn't make it clear that it includes
> "AnonHugePages". I'll also make it clear in the text that mentions AnonHugePages
> counter that it "only applies to traditional PMD-sized THP for historical
> reasons" and that "AnonHugePages should have been called AnonHugePmdMapped" as
> David suggested in the other thread.
OK.
Are we entirely dropping the AnonHugePtePages that was there in v6? I'm
looking for some way to monitor this. I may have missed it because I haven't
gone through all of v7 yet.
...
>>> -"THPeligible" indicates whether the mapping is eligible for allocating THP
>>> -pages as well as the THP is PMD mappable or not - 1 if true, 0 otherwise.
>>> -It just shows the current status.
>>> +"THPeligible" indicates whether the mapping is eligible for allocating
>>> +naturally aligned THP pages of any currently enabled size. 1 if true, 0
>>> +otherwise. It just shows the current status.
>>
>> "It just shows the current status"...as opposed to what? I'm missing an
>> educational opportunity here--not sure what this means. :)
>
> I have no idea either - it seems superfluous. But that sentence was there
> already. I can remove it if you like?
>
Yes, let's remove it, please.
...
>>> +/*
>>> + * Mask of all large folio orders supported for anonymous THP.
>>> + */
>>> +#define THP_ORDERS_ALL_ANON BIT(PMD_ORDER)
>>> +
>>> +/*
>>> + * Mask of all large folio orders supported for file THP.
>>> + */
>>> +#define THP_ORDERS_ALL_FILE (BIT(PMD_ORDER) | BIT(PUD_ORDER))
>>
>> Is there something about file THP that implies PUD_ORDER? This
>> deserves an explanatory comment, I think.
>
> Sorry, I'm not really sure what you are asking? Today's kernel supports
> PUD-mapping file-backed memory (mostly DAX I believe). I'm not sure what comment
> you want me to add, other than "file-backed memory can support PUD-mapping", but
> that's self-evident from the define, isn't it?
>
Well, it's sort of evident, but confusing to me anyway, because it
combines THP and PUD. Which seems to imply that we have PUD-based THPs
supported, but only for file-backed mappings. Which is weird and needs
some explanation, right?
>>
>>> +
>>> +/*
>>> + * Mask of all large folio orders supported for THP.
>>> + */
>>> +#define THP_ORDERS_ALL (THP_ORDERS_ALL_ANON | THP_ORDERS_ALL_FILE)
>>> +
>>> #ifdef CONFIG_TRANSPARENT_HUGEPAGE
>>> #define HPAGE_PMD_SHIFT PMD_SHIFT
>>> #define HPAGE_PMD_SIZE ((1UL) << HPAGE_PMD_SHIFT)
>>> @@ -78,13 +93,18 @@ extern struct kobj_attribute shmem_enabled_attr;
>>>
>>> extern unsigned long transparent_hugepage_flags;
>>>
>>> -#define hugepage_flags_enabled() \
>>> - (transparent_hugepage_flags & \
>>> - ((1<<TRANSPARENT_HUGEPAGE_FLAG) | \
>>> - (1<<TRANSPARENT_HUGEPAGE_REQ_MADV_FLAG)))
>>> -#define hugepage_flags_always() \
>>> - (transparent_hugepage_flags & \
>>> - (1<<TRANSPARENT_HUGEPAGE_FLAG))
>>
>> Are macros actually required? If not, static inlines would be nicer.
>
> I agree static inlines are nicer. Here I'm removing existing macros though, and
Oh, I see that I replied in the wrong part of the email, since that's the
*removal* part. oops. :)
...
>>> -static inline bool transhuge_vma_suitable(struct vm_area_struct *vma,
>>> - unsigned long addr)
>>> -{
>>> - unsigned long haddr;
>>> -
>>> - /* Don't have to check pgoff for anonymous vma */
>>> - if (!vma_is_anonymous(vma)) {
>>> - if (!IS_ALIGNED((vma->vm_start >> PAGE_SHIFT) - vma->vm_pgoff,
>>> - HPAGE_PMD_NR))
>>> - return false;
>>> +static inline unsigned long transhuge_vma_suitable(struct vm_area_struct *vma,
>>> + unsigned long addr, unsigned long orders)
>>
>> Changing this from a bool to a mask of orders is quite significant, and
>> both the function name and the function-level comment documentation need
>> to also be adjusted. Here, perhaps one of these names would work:
>>
>> transhuge_vma_suitable_orders()
>
> This is my preference, but its getting a bit long. How about:
>
> thp_vma_suitable_orders()
>
> I could then call the other one:
>
> thp_vma_allowable_orders()
>
> So we have a clearly related pair?
Oh yes, that works nicely.
>
>
>> transhuge_vma_orders()>
>>
>>> +{
>>> + int order;
>>> +
>>> + /*
>>> + * Iterate over orders, highest to lowest, removing orders that don't
>>> + * meet alignment requirements from the set. Exit loop at first order
>>> + * that meets requirements, since all lower orders must also meet
>>> + * requirements.
>>
>> Should we add a little note here, to the effect of, "this is unilaterally
>> taking over a certain amount of allocation-like policy, by deciding how
>> to search for folios of a certain size"?
>>
>> Or is this The Only Way To Do It, after all? I know we had some discussion
>> about it, and intuitively it feels reasonable, but wanted to poke at it
>> one last time anyway.
>
> This function isn't trying to implement policy, its just filtering out orders
> that don't fit and therefore definitely cannot be used. The result is a set of
> orders the could be used and its the policy maker's job to decide which one.
> Currently that policy is "biggest one that fits && does not overlap other
> non-none ptes && folio successfully allocated". That's implemented in the next
> patch and would potentially be swapped out in the future for something more
> exotic/optimal.
>
> So I don't think we need any extra comments here.
Ack.
...
>>> -bool hugepage_vma_check(struct vm_area_struct *vma, unsigned long vm_flags,
>>> - bool smaps, bool in_pf, bool enforce_sysfs)
>>> +#define hugepage_global_enabled() \
>>> + (transparent_hugepage_flags & \
>>> + ((1<<TRANSPARENT_HUGEPAGE_FLAG) | \
>>> + (1<<TRANSPARENT_HUGEPAGE_REQ_MADV_FLAG)))
>>> +
>>> +#define hugepage_global_always() \
>>> + (transparent_hugepage_flags & \
>>> + (1<<TRANSPARENT_HUGEPAGE_FLAG))
>>> +
>>
>> Here again, I'd like to request that we avoid macros, as I don't think
>> they are strictly required.
>
> Yeah I agree. I did them this way, because they already existed and I was just
> moving them from the header to here. But I'll change to static inline.
>
>>
>>> +bool hugepage_flags_enabled(void)
>>> {
>>> + /*
>>> + * We cover both the anon and the file-backed case here; we must return
>>> + * true if globally enabled, even when all anon sizes are set to never.
>>> + * So we don't need to look at huge_anon_orders_global.
>>> + */
>>> + return hugepage_global_enabled() ||
>>> + huge_anon_orders_always ||
>>> + huge_anon_orders_madvise;
>>> +}
>>> +
>>> +/**
>>> + * hugepage_vma_check - determine which hugepage orders can be applied to vma
>>> + * @vma: the vm area to check
>>> + * @vm_flags: use these vm_flags instead of vma->vm_flags
>>> + * @smaps: whether answer will be used for smaps file
>>> + * @in_pf: whether answer will be used by page fault handler
>>> + * @enforce_sysfs: whether sysfs config should be taken into account
>>> + * @orders: bitfield of all orders to consider
>>> + *
>>> + * Calculates the intersection of the requested hugepage orders and the allowed
>>> + * hugepage orders for the provided vma. Permitted orders are encoded as a set
>>> + * bit at the corresponding bit position (bit-2 corresponds to order-2, bit-3
>>> + * corresponds to order-3, etc). Order-0 is never considered a hugepage order.
>>> + *
>>> + * Return: bitfield of orders allowed for hugepage in the vma. 0 if no hugepage
>>> + * orders are allowed.
>>> + */
>>> +unsigned long hugepage_vma_check(struct vm_area_struct *vma,
>>> + unsigned long vm_flags, bool smaps, bool in_pf,
>>> + bool enforce_sysfs, unsigned long orders)
>>
>> Here again, a bool return type has been changed to a bitfield. Let's
>> also update the function name. Maybe one of these:
>>
>> hugepage_vma_orders()
>> hugepage_vma_allowable_orders()
>
> thp_vma_allowable_orders()?
>
Even better, yes.
thanks,
On 29/11/2023 19:40, John Hubbard wrote:
> 1On 11/29/23 03:05, Ryan Roberts wrote:
>> On 29/11/2023 03:42, John Hubbard wrote:
>>> On 11/22/23 08:29, Ryan Roberts wrote:
> ...
>>>> +As well as PMD-sized THP described above, it is also possible to
>>>> +configure the system to allocate "small-sized THP" to back anonymous
>>>
>>> Here's one of the places to change to the new name, which lately is
>>> "multi-size THP", or mTHP or m_thp for short. (I've typed "multi-size"
>>> instead of "multi-sized", because the 'd' doesn't add significantly to
>>> the meaning, and if in doubt, shorter is better.
>>
>> I was thinking of some light changes to the start of this paragraph, something
>> like:
>>
>> Modern kernels support "multi-size THP" (mTHP), which introduces the ability to
>> allocate memory in blocks that are bigger than a base page but smaller than
>> traditional PMD-size (as described above, in increments of a power-of-2 number
>> of pages. mTHP can back anonymous
>>
>
> Very nice.
>
>
> ...
>>> By default, PMD-sized hugepages have enabled="inherited" and all other
>>> hugepage sizes have enabled="never".
>>
>> That all sounds good; will update.
>>
>> I wonder if "inherit" is even better than "inherited" though?
>
> Yes, I think so. "inherit" was actually my first idea, and after
> thinking about it, I just made it worse by adding the "ed". haha. :)
>
> ...
>>>> Khugepaged controls
>>>> -------------------
>>>>
>>>> +.. note::
>>>> + khugepaged currently only searches for opportunities to collapse to
>>>> + PMD-sized THP and no attempt is made to collapse to small-sized
>>>> + THP.
>>>> +
>>
>> "small-sized THP" used here too; I propose to change it to "... collapse to
>> other THP sizes."
>
> OK, looks good.
>
>>
>>>> khugepaged runs usually at low frequency so while one may not want to
>>>> invoke defrag algorithms synchronously during the page faults, it
>>>> should be worth invoking defrag at least in khugepaged. However it's
>>>> @@ -282,10 +321,11 @@ force
>>>> Need of application restart
>>>> ===========================
>>>>
>>>> -The transparent_hugepage/enabled values and tmpfs mount option only affect
>>>> -future behavior. So to make them effective you need to restart any
>>>> -application that could have been using hugepages. This also applies to the
>>>> -regions registered in khugepaged.
>>>> +The transparent_hugepage/enabled and
>>>> +transparent_hugepage/hugepages-<size>kB/enabled values and tmpfs mount
>>>> +option only affect future behavior. So to make them effective you need
>>>> +to restart any application that could have been using hugepages. This
>>>> +also applies to the regions registered in khugepaged.
>>>>
>>>> Monitoring usage
>>>> ================
>>>> @@ -308,6 +348,10 @@ frequently will incur overhead.
>>>> There are a number of counters in ``/proc/vmstat`` that may be used to
>>>> monitor how successfully the system is providing huge pages for use.
>>>>
>>>> +.. note::
>>>> + Currently the below counters only record events relating to
>>>> + PMD-sized THP. Events relating to small-sized THP are not included.
>>>
>>> Here's another spot to rename to "multi-size THP".
>>
>> I propose to change it to "Events relating to other THP sizes..."
>>
>> I'm also going to move this note to just under the "Monitoring Usage" heading
>> since its current position doesn't make it clear that it includes
>> "AnonHugePages". I'll also make it clear in the text that mentions AnonHugePages
>> counter that it "only applies to traditional PMD-sized THP for historical
>> reasons" and that "AnonHugePages should have been called AnonHugePmdMapped" as
>> David suggested in the other thread.
>
> OK.
>
> Are we entirely dropping the AnonHugePtePages that was there in v6? I'm
Yes, afraid so. David raised some concerns about the semantics of the counters
and also highlighted that (Greg KH?) doesn't want to see sysfs files with
multiple values so we might need to design a whole new interface eventually.
> looking for some way to monitor this. I may have missed it because I haven't
> gone through all of v7 yet.
>
> ...
>>>> -"THPeligible" indicates whether the mapping is eligible for allocating THP
>>>> -pages as well as the THP is PMD mappable or not - 1 if true, 0 otherwise.
>>>> -It just shows the current status.
>>>> +"THPeligible" indicates whether the mapping is eligible for allocating
>>>> +naturally aligned THP pages of any currently enabled size. 1 if true, 0
>>>> +otherwise. It just shows the current status.
>>>
>>> "It just shows the current status"...as opposed to what? I'm missing an
>>> educational opportunity here--not sure what this means. :)
>>
>> I have no idea either - it seems superfluous. But that sentence was there
>> already. I can remove it if you like?
>>
>
> Yes, let's remove it, please.
>
> ...
>>>> +/*
>>>> + * Mask of all large folio orders supported for anonymous THP.
>>>> + */
>>>> +#define THP_ORDERS_ALL_ANON BIT(PMD_ORDER)
>>>> +
>>>> +/*
>>>> + * Mask of all large folio orders supported for file THP.
>>>> + */
>>>> +#define THP_ORDERS_ALL_FILE (BIT(PMD_ORDER) | BIT(PUD_ORDER))
>>>
>>> Is there something about file THP that implies PUD_ORDER? This
>>> deserves an explanatory comment, I think.
>>
>> Sorry, I'm not really sure what you are asking? Today's kernel supports
>> PUD-mapping file-backed memory (mostly DAX I believe). I'm not sure what comment
>> you want me to add, other than "file-backed memory can support PUD-mapping", but
>> that's self-evident from the define, isn't it?
>>
>
> Well, it's sort of evident, but confusing to me anyway, because it
> combines THP and PUD. Which seems to imply that we have PUD-based THPs
> supported, but only for file-backed mappings. Which is weird and needs
> some explanation, right?
Ahh yes, you have fallen into the trap of thinking that until this point THP is
PMD-size only, which indeed is not the case for file-backed mappings; they
already support PMD- and PUD-size. And this is another reason why I think its OK
to continue to call the new sizes "THP".
I'm still not sure what you want me to explain in the code though... It's an
existing feature.
>
>>>
>>>> +
>>>> +/*
>>>> + * Mask of all large folio orders supported for THP.
>>>> + */
>>>> +#define THP_ORDERS_ALL (THP_ORDERS_ALL_ANON | THP_ORDERS_ALL_FILE)
>>>> +
>>>> #ifdef CONFIG_TRANSPARENT_HUGEPAGE
>>>> #define HPAGE_PMD_SHIFT PMD_SHIFT
>>>> #define HPAGE_PMD_SIZE ((1UL) << HPAGE_PMD_SHIFT)
>>>> @@ -78,13 +93,18 @@ extern struct kobj_attribute shmem_enabled_attr;
>>>>
>>>> extern unsigned long transparent_hugepage_flags;
>>>>
>>>> -#define hugepage_flags_enabled() \
>>>> - (transparent_hugepage_flags & \
>>>> - ((1<<TRANSPARENT_HUGEPAGE_FLAG) | \
>>>> - (1<<TRANSPARENT_HUGEPAGE_REQ_MADV_FLAG)))
>>>> -#define hugepage_flags_always() \
>>>> - (transparent_hugepage_flags & \
>>>> - (1<<TRANSPARENT_HUGEPAGE_FLAG))
>>>
>>> Are macros actually required? If not, static inlines would be nicer.
>>
>> I agree static inlines are nicer. Here I'm removing existing macros though, and
>
> Oh, I see that I replied in the wrong part of the email, since that's the
> *removal* part. oops. :)
>
> ...
>>>> -static inline bool transhuge_vma_suitable(struct vm_area_struct *vma,
>>>> - unsigned long addr)
>>>> -{
>>>> - unsigned long haddr;
>>>> -
>>>> - /* Don't have to check pgoff for anonymous vma */
>>>> - if (!vma_is_anonymous(vma)) {
>>>> - if (!IS_ALIGNED((vma->vm_start >> PAGE_SHIFT) - vma->vm_pgoff,
>>>> - HPAGE_PMD_NR))
>>>> - return false;
>>>> +static inline unsigned long transhuge_vma_suitable(struct vm_area_struct *vma,
>>>> + unsigned long addr, unsigned long orders)
>>>
>>> Changing this from a bool to a mask of orders is quite significant, and
>>> both the function name and the function-level comment documentation need
>>> to also be adjusted. Here, perhaps one of these names would work:
>>>
>>> transhuge_vma_suitable_orders()
>>
>> This is my preference, but its getting a bit long. How about:
>>
>> thp_vma_suitable_orders()
>>
>> I could then call the other one:
>>
>> thp_vma_allowable_orders()
>>
>> So we have a clearly related pair?
>
> Oh yes, that works nicely.
>
>>
>>
>>> transhuge_vma_orders()>
>>>
>>>> +{
>>>> + int order;
>>>> +
>>>> + /*
>>>> + * Iterate over orders, highest to lowest, removing orders that don't
>>>> + * meet alignment requirements from the set. Exit loop at first order
>>>> + * that meets requirements, since all lower orders must also meet
>>>> + * requirements.
>>>
>>> Should we add a little note here, to the effect of, "this is unilaterally
>>> taking over a certain amount of allocation-like policy, by deciding how
>>> to search for folios of a certain size"?
>>>
>>> Or is this The Only Way To Do It, after all? I know we had some discussion
>>> about it, and intuitively it feels reasonable, but wanted to poke at it
>>> one last time anyway.
>>
>> This function isn't trying to implement policy, its just filtering out orders
>> that don't fit and therefore definitely cannot be used. The result is a set of
>> orders the could be used and its the policy maker's job to decide which one.
>> Currently that policy is "biggest one that fits && does not overlap other
>> non-none ptes && folio successfully allocated". That's implemented in the next
>> patch and would potentially be swapped out in the future for something more
>> exotic/optimal.
>>
>> So I don't think we need any extra comments here.
>
> Ack.
>
> ...
>>>> -bool hugepage_vma_check(struct vm_area_struct *vma, unsigned long vm_flags,
>>>> - bool smaps, bool in_pf, bool enforce_sysfs)
>>>> +#define hugepage_global_enabled() \
>>>> + (transparent_hugepage_flags & \
>>>> + ((1<<TRANSPARENT_HUGEPAGE_FLAG) | \
>>>> + (1<<TRANSPARENT_HUGEPAGE_REQ_MADV_FLAG)))
>>>> +
>>>> +#define hugepage_global_always() \
>>>> + (transparent_hugepage_flags & \
>>>> + (1<<TRANSPARENT_HUGEPAGE_FLAG))
>>>> +
>>>
>>> Here again, I'd like to request that we avoid macros, as I don't think
>>> they are strictly required.
>>
>> Yeah I agree. I did them this way, because they already existed and I was just
>> moving them from the header to here. But I'll change to static inline.
>>
>>>
>>>> +bool hugepage_flags_enabled(void)
>>>> {
>>>> + /*
>>>> + * We cover both the anon and the file-backed case here; we must return
>>>> + * true if globally enabled, even when all anon sizes are set to never.
>>>> + * So we don't need to look at huge_anon_orders_global.
>>>> + */
>>>> + return hugepage_global_enabled() ||
>>>> + huge_anon_orders_always ||
>>>> + huge_anon_orders_madvise;
>>>> +}
>>>> +
>>>> +/**
>>>> + * hugepage_vma_check - determine which hugepage orders can be applied to vma
>>>> + * @vma: the vm area to check
>>>> + * @vm_flags: use these vm_flags instead of vma->vm_flags
>>>> + * @smaps: whether answer will be used for smaps file
>>>> + * @in_pf: whether answer will be used by page fault handler
>>>> + * @enforce_sysfs: whether sysfs config should be taken into account
>>>> + * @orders: bitfield of all orders to consider
>>>> + *
>>>> + * Calculates the intersection of the requested hugepage orders and the
>>>> allowed
>>>> + * hugepage orders for the provided vma. Permitted orders are encoded as a set
>>>> + * bit at the corresponding bit position (bit-2 corresponds to order-2, bit-3
>>>> + * corresponds to order-3, etc). Order-0 is never considered a hugepage order.
>>>> + *
>>>> + * Return: bitfield of orders allowed for hugepage in the vma. 0 if no
>>>> hugepage
>>>> + * orders are allowed.
>>>> + */
>>>> +unsigned long hugepage_vma_check(struct vm_area_struct *vma,
>>>> + unsigned long vm_flags, bool smaps, bool in_pf,
>>>> + bool enforce_sysfs, unsigned long orders)
>>>
>>> Here again, a bool return type has been changed to a bitfield. Let's
>>> also update the function name. Maybe one of these:
>>>
>>> hugepage_vma_orders()
>>> hugepage_vma_allowable_orders()
>>
>> thp_vma_allowable_orders()?
>>
>
> Even better, yes.
Great thanks for the review! I'll get all these changes folded in and if I don't
get any further feedback by the end of the week, I'll repost on Monday.
>
>
> thanks,
@@ -45,10 +45,23 @@ components:
the two is using hugepages just because of the fact the TLB miss is
going to run faster.
+As well as PMD-sized THP described above, it is also possible to
+configure the system to allocate "small-sized THP" to back anonymous
+memory (for example 16K, 32K, 64K, etc). These THPs continue to be
+PTE-mapped, but in many cases can still provide similar benefits to
+those outlined above: Page faults are significantly reduced (by a
+factor of e.g. 4, 8, 16, etc), but latency spikes are much less
+prominent because the size of each page isn't as huge as the PMD-sized
+variant and there is less memory to clear in each page fault. Some
+architectures also employ TLB compression mechanisms to squeeze more
+entries in when a set of PTEs are virtually and physically contiguous
+and approporiately aligned. In this case, TLB misses will occur less
+often.
+
THP can be enabled system wide or restricted to certain tasks or even
memory ranges inside task's address space. Unless THP is completely
disabled, there is ``khugepaged`` daemon that scans memory and
-collapses sequences of basic pages into huge pages.
+collapses sequences of basic pages into PMD-sized huge pages.
The THP behaviour is controlled via :ref:`sysfs <thp_sysfs>`
interface and using madvise(2) and prctl(2) system calls.
@@ -95,12 +108,29 @@ Global THP controls
Transparent Hugepage Support for anonymous memory can be entirely disabled
(mostly for debugging purposes) or only enabled inside MADV_HUGEPAGE
regions (to avoid the risk of consuming more memory resources) or enabled
-system wide. This can be achieved with one of::
+system wide. This can be achieved per-supported-THP-size with one of::
+
+ echo always >/sys/kernel/mm/transparent_hugepage/hugepages-<size>kB/enabled
+ echo madvise >/sys/kernel/mm/transparent_hugepage/hugepages-<size>kB/enabled
+ echo never >/sys/kernel/mm/transparent_hugepage/hugepages-<size>kB/enabled
+
+where <size> is the hugepage size being addressed, the available sizes
+for which vary by system. Alternatively it is possible to specify that
+a given hugepage size will inherrit the global enabled setting::
+
+ echo global >/sys/kernel/mm/transparent_hugepage/hugepages-<size>kB/enabled
+
+The global (legacy) enabled setting can be set as follows::
echo always >/sys/kernel/mm/transparent_hugepage/enabled
echo madvise >/sys/kernel/mm/transparent_hugepage/enabled
echo never >/sys/kernel/mm/transparent_hugepage/enabled
+By default, PMD-sized hugepages have enabled="global" and all other
+hugepage sizes have enabled="never". If enabling multiple hugepage
+sizes, the kernel will select the most appropriate enabled size for a
+given allocation.
+
It's also possible to limit defrag efforts in the VM to generate
anonymous hugepages in case they're not immediately free to madvise
regions or to never try to defrag memory and simply fallback to regular
@@ -146,25 +176,34 @@ madvise
never
should be self-explanatory.
-By default kernel tries to use huge zero page on read page fault to
-anonymous mapping. It's possible to disable huge zero page by writing 0
-or enable it back by writing 1::
+By default kernel tries to use huge, PMD-mappable zero page on read
+page fault to anonymous mapping. It's possible to disable huge zero
+page by writing 0 or enable it back by writing 1::
echo 0 >/sys/kernel/mm/transparent_hugepage/use_zero_page
echo 1 >/sys/kernel/mm/transparent_hugepage/use_zero_page
-Some userspace (such as a test program, or an optimized memory allocation
-library) may want to know the size (in bytes) of a transparent hugepage::
+Some userspace (such as a test program, or an optimized memory
+allocation library) may want to know the size (in bytes) of a
+PMD-mappable transparent hugepage::
cat /sys/kernel/mm/transparent_hugepage/hpage_pmd_size
-khugepaged will be automatically started when
-transparent_hugepage/enabled is set to "always" or "madvise, and it'll
-be automatically shutdown if it's set to "never".
+khugepaged will be automatically started when one or more hugepage
+sizes are enabled (either by directly setting "always" or "madvise",
+or by setting "global" while the global enabled is set to "always" or
+"madvise"), and it'll be automatically shutdown when the last hugepage
+size is disabled (either by directly setting "never", or by setting
+"global" while the global enabled is set to "never").
Khugepaged controls
-------------------
+.. note::
+ khugepaged currently only searches for opportunities to collapse to
+ PMD-sized THP and no attempt is made to collapse to small-sized
+ THP.
+
khugepaged runs usually at low frequency so while one may not want to
invoke defrag algorithms synchronously during the page faults, it
should be worth invoking defrag at least in khugepaged. However it's
@@ -282,10 +321,11 @@ force
Need of application restart
===========================
-The transparent_hugepage/enabled values and tmpfs mount option only affect
-future behavior. So to make them effective you need to restart any
-application that could have been using hugepages. This also applies to the
-regions registered in khugepaged.
+The transparent_hugepage/enabled and
+transparent_hugepage/hugepages-<size>kB/enabled values and tmpfs mount
+option only affect future behavior. So to make them effective you need
+to restart any application that could have been using hugepages. This
+also applies to the regions registered in khugepaged.
Monitoring usage
================
@@ -308,6 +348,10 @@ frequently will incur overhead.
There are a number of counters in ``/proc/vmstat`` that may be used to
monitor how successfully the system is providing huge pages for use.
+.. note::
+ Currently the below counters only record events relating to
+ PMD-sized THP. Events relating to small-sized THP are not included.
+
thp_fault_alloc
is incremented every time a huge page is successfully
allocated to handle a page fault.
@@ -413,7 +457,7 @@ for huge pages.
Optimizing the applications
===========================
-To be guaranteed that the kernel will map a 2M page immediately in any
+To be guaranteed that the kernel will map a THP immediately in any
memory region, the mmap region has to be hugepage naturally
aligned. posix_memalign() can provide that guarantee.
@@ -528,9 +528,9 @@ replaced by copy-on-write) part of the underlying shmem object out on swap.
does not take into account swapped out page of underlying shmem objects.
"Locked" indicates whether the mapping is locked in memory or not.
-"THPeligible" indicates whether the mapping is eligible for allocating THP
-pages as well as the THP is PMD mappable or not - 1 if true, 0 otherwise.
-It just shows the current status.
+"THPeligible" indicates whether the mapping is eligible for allocating
+naturally aligned THP pages of any currently enabled size. 1 if true, 0
+otherwise. It just shows the current status.
"VmFlags" field deserves a separate description. This member represents the
kernel flags associated with the particular virtual memory area in two letter
@@ -865,7 +865,8 @@ static int show_smap(struct seq_file *m, void *v)
__show_smap(m, &mss, false);
seq_printf(m, "THPeligible: %8u\n",
- hugepage_vma_check(vma, vma->vm_flags, true, false, true));
+ !!hugepage_vma_check(vma, vma->vm_flags, true, false, true,
+ THP_ORDERS_ALL));
if (arch_pkeys_enabled())
seq_printf(m, "ProtectionKey: %8u\n", vma_pkey(vma));
@@ -67,6 +67,21 @@ extern struct kobj_attribute shmem_enabled_attr;
#define HPAGE_PMD_ORDER (HPAGE_PMD_SHIFT-PAGE_SHIFT)
#define HPAGE_PMD_NR (1<<HPAGE_PMD_ORDER)
+/*
+ * Mask of all large folio orders supported for anonymous THP.
+ */
+#define THP_ORDERS_ALL_ANON BIT(PMD_ORDER)
+
+/*
+ * Mask of all large folio orders supported for file THP.
+ */
+#define THP_ORDERS_ALL_FILE (BIT(PMD_ORDER) | BIT(PUD_ORDER))
+
+/*
+ * Mask of all large folio orders supported for THP.
+ */
+#define THP_ORDERS_ALL (THP_ORDERS_ALL_ANON | THP_ORDERS_ALL_FILE)
+
#ifdef CONFIG_TRANSPARENT_HUGEPAGE
#define HPAGE_PMD_SHIFT PMD_SHIFT
#define HPAGE_PMD_SIZE ((1UL) << HPAGE_PMD_SHIFT)
@@ -78,13 +93,18 @@ extern struct kobj_attribute shmem_enabled_attr;
extern unsigned long transparent_hugepage_flags;
-#define hugepage_flags_enabled() \
- (transparent_hugepage_flags & \
- ((1<<TRANSPARENT_HUGEPAGE_FLAG) | \
- (1<<TRANSPARENT_HUGEPAGE_REQ_MADV_FLAG)))
-#define hugepage_flags_always() \
- (transparent_hugepage_flags & \
- (1<<TRANSPARENT_HUGEPAGE_FLAG))
+bool hugepage_flags_enabled(void);
+
+static inline int first_order(unsigned long orders)
+{
+ return fls_long(orders) - 1;
+}
+
+static inline int next_order(unsigned long *orders, int prev)
+{
+ *orders &= ~BIT(prev);
+ return first_order(*orders);
+}
/*
* Do the below checks:
@@ -97,23 +117,39 @@ extern unsigned long transparent_hugepage_flags;
* - For all vmas, check if the haddr is in an aligned HPAGE_PMD_SIZE
* area.
*/
-static inline bool transhuge_vma_suitable(struct vm_area_struct *vma,
- unsigned long addr)
-{
- unsigned long haddr;
-
- /* Don't have to check pgoff for anonymous vma */
- if (!vma_is_anonymous(vma)) {
- if (!IS_ALIGNED((vma->vm_start >> PAGE_SHIFT) - vma->vm_pgoff,
- HPAGE_PMD_NR))
- return false;
+static inline unsigned long transhuge_vma_suitable(struct vm_area_struct *vma,
+ unsigned long addr, unsigned long orders)
+{
+ int order;
+
+ /*
+ * Iterate over orders, highest to lowest, removing orders that don't
+ * meet alignment requirements from the set. Exit loop at first order
+ * that meets requirements, since all lower orders must also meet
+ * requirements.
+ */
+
+ order = first_order(orders);
+
+ while (orders) {
+ unsigned long hpage_size = PAGE_SIZE << order;
+ unsigned long haddr = ALIGN_DOWN(addr, hpage_size);
+
+ if (haddr >= vma->vm_start &&
+ haddr + hpage_size <= vma->vm_end) {
+ if (!vma_is_anonymous(vma)) {
+ if (IS_ALIGNED((vma->vm_start >> PAGE_SHIFT) -
+ vma->vm_pgoff,
+ hpage_size >> PAGE_SHIFT))
+ break;
+ } else
+ break;
+ }
+
+ order = next_order(&orders, order);
}
- haddr = addr & HPAGE_PMD_MASK;
-
- if (haddr < vma->vm_start || haddr + HPAGE_PMD_SIZE > vma->vm_end)
- return false;
- return true;
+ return orders;
}
static inline bool file_thp_enabled(struct vm_area_struct *vma)
@@ -130,8 +166,9 @@ static inline bool file_thp_enabled(struct vm_area_struct *vma)
!inode_is_open_for_write(inode) && S_ISREG(inode->i_mode);
}
-bool hugepage_vma_check(struct vm_area_struct *vma, unsigned long vm_flags,
- bool smaps, bool in_pf, bool enforce_sysfs);
+unsigned long hugepage_vma_check(struct vm_area_struct *vma,
+ unsigned long vm_flags, bool smaps, bool in_pf,
+ bool enforce_sysfs, unsigned long orders);
#define transparent_hugepage_use_zero_page() \
(transparent_hugepage_flags & \
@@ -267,17 +304,18 @@ static inline bool folio_test_pmd_mappable(struct folio *folio)
return false;
}
-static inline bool transhuge_vma_suitable(struct vm_area_struct *vma,
- unsigned long addr)
+static inline unsigned long transhuge_vma_suitable(struct vm_area_struct *vma,
+ unsigned long addr, unsigned long orders)
{
- return false;
+ return 0;
}
-static inline bool hugepage_vma_check(struct vm_area_struct *vma,
- unsigned long vm_flags, bool smaps,
- bool in_pf, bool enforce_sysfs)
+static inline unsigned long hugepage_vma_check(struct vm_area_struct *vma,
+ unsigned long vm_flags, bool smaps,
+ bool in_pf, bool enforce_sysfs,
+ unsigned long orders)
{
- return false;
+ return 0;
}
static inline void folio_prep_large_rmappable(struct folio *folio) {}
@@ -74,12 +74,60 @@ static unsigned long deferred_split_scan(struct shrinker *shrink,
static atomic_t huge_zero_refcount;
struct page *huge_zero_page __read_mostly;
unsigned long huge_zero_pfn __read_mostly = ~0UL;
+static unsigned long huge_anon_orders_always __read_mostly;
+static unsigned long huge_anon_orders_madvise __read_mostly;
+static unsigned long huge_anon_orders_global __read_mostly;
-bool hugepage_vma_check(struct vm_area_struct *vma, unsigned long vm_flags,
- bool smaps, bool in_pf, bool enforce_sysfs)
+#define hugepage_global_enabled() \
+ (transparent_hugepage_flags & \
+ ((1<<TRANSPARENT_HUGEPAGE_FLAG) | \
+ (1<<TRANSPARENT_HUGEPAGE_REQ_MADV_FLAG)))
+
+#define hugepage_global_always() \
+ (transparent_hugepage_flags & \
+ (1<<TRANSPARENT_HUGEPAGE_FLAG))
+
+bool hugepage_flags_enabled(void)
{
+ /*
+ * We cover both the anon and the file-backed case here; we must return
+ * true if globally enabled, even when all anon sizes are set to never.
+ * So we don't need to look at huge_anon_orders_global.
+ */
+ return hugepage_global_enabled() ||
+ huge_anon_orders_always ||
+ huge_anon_orders_madvise;
+}
+
+/**
+ * hugepage_vma_check - determine which hugepage orders can be applied to vma
+ * @vma: the vm area to check
+ * @vm_flags: use these vm_flags instead of vma->vm_flags
+ * @smaps: whether answer will be used for smaps file
+ * @in_pf: whether answer will be used by page fault handler
+ * @enforce_sysfs: whether sysfs config should be taken into account
+ * @orders: bitfield of all orders to consider
+ *
+ * Calculates the intersection of the requested hugepage orders and the allowed
+ * hugepage orders for the provided vma. Permitted orders are encoded as a set
+ * bit at the corresponding bit position (bit-2 corresponds to order-2, bit-3
+ * corresponds to order-3, etc). Order-0 is never considered a hugepage order.
+ *
+ * Return: bitfield of orders allowed for hugepage in the vma. 0 if no hugepage
+ * orders are allowed.
+ */
+unsigned long hugepage_vma_check(struct vm_area_struct *vma,
+ unsigned long vm_flags, bool smaps, bool in_pf,
+ bool enforce_sysfs, unsigned long orders)
+{
+ /* Check the intersection of requested and supported orders. */
+ orders &= vma_is_anonymous(vma) ?
+ THP_ORDERS_ALL_ANON : THP_ORDERS_ALL_FILE;
+ if (!orders)
+ return 0;
+
if (!vma->vm_mm) /* vdso */
- return false;
+ return 0;
/*
* Explicitly disabled through madvise or prctl, or some
@@ -88,16 +136,16 @@ bool hugepage_vma_check(struct vm_area_struct *vma, unsigned long vm_flags,
* */
if ((vm_flags & VM_NOHUGEPAGE) ||
test_bit(MMF_DISABLE_THP, &vma->vm_mm->flags))
- return false;
+ return 0;
/*
* If the hardware/firmware marked hugepage support disabled.
*/
if (transparent_hugepage_flags & (1 << TRANSPARENT_HUGEPAGE_UNSUPPORTED))
- return false;
+ return 0;
/* khugepaged doesn't collapse DAX vma, but page fault is fine. */
if (vma_is_dax(vma))
- return in_pf;
+ return in_pf ? orders : 0;
/*
* khugepaged special VMA and hugetlb VMA.
@@ -105,17 +153,29 @@ bool hugepage_vma_check(struct vm_area_struct *vma, unsigned long vm_flags,
* VM_MIXEDMAP set.
*/
if (!in_pf && !smaps && (vm_flags & VM_NO_KHUGEPAGED))
- return false;
+ return 0;
/*
- * Check alignment for file vma and size for both file and anon vma.
+ * Check alignment for file vma and size for both file and anon vma by
+ * filtering out the unsuitable orders.
*
* Skip the check for page fault. Huge fault does the check in fault
- * handlers. And this check is not suitable for huge PUD fault.
+ * handlers.
*/
- if (!in_pf &&
- !transhuge_vma_suitable(vma, (vma->vm_end - HPAGE_PMD_SIZE)))
- return false;
+ if (!in_pf) {
+ int order = first_order(orders);
+ unsigned long addr;
+
+ while (orders) {
+ addr = vma->vm_end - (PAGE_SIZE << order);
+ if (transhuge_vma_suitable(vma, addr, BIT(order)))
+ break;
+ order = next_order(&orders, order);
+ }
+
+ if (!orders)
+ return 0;
+ }
/*
* Enabled via shmem mount options or sysfs settings.
@@ -124,13 +184,27 @@ bool hugepage_vma_check(struct vm_area_struct *vma, unsigned long vm_flags,
*/
if (!in_pf && shmem_file(vma->vm_file))
return shmem_is_huge(file_inode(vma->vm_file), vma->vm_pgoff,
- !enforce_sysfs, vma->vm_mm, vm_flags);
+ !enforce_sysfs, vma->vm_mm, vm_flags)
+ ? orders : 0;
/* Enforce sysfs THP requirements as necessary */
- if (enforce_sysfs &&
- (!hugepage_flags_enabled() || (!(vm_flags & VM_HUGEPAGE) &&
- !hugepage_flags_always())))
- return false;
+ if (enforce_sysfs) {
+ if (vma_is_anonymous(vma)) {
+ unsigned long mask = READ_ONCE(huge_anon_orders_always);
+
+ if (vm_flags & VM_HUGEPAGE)
+ mask |= READ_ONCE(huge_anon_orders_madvise);
+ if (hugepage_global_always() ||
+ ((vm_flags & VM_HUGEPAGE) && hugepage_global_enabled()))
+ mask |= READ_ONCE(huge_anon_orders_global);
+
+ orders &= mask;
+ if (!orders)
+ return 0;
+ } else if (!hugepage_global_enabled() ||
+ (!(vm_flags & VM_HUGEPAGE) && !hugepage_global_always()))
+ return 0;
+ }
if (!vma_is_anonymous(vma)) {
/*
@@ -138,15 +212,15 @@ bool hugepage_vma_check(struct vm_area_struct *vma, unsigned long vm_flags,
* in fault path.
*/
if (((in_pf || smaps)) && vma->vm_ops->huge_fault)
- return true;
+ return orders;
/* Only regular file is valid in collapse path */
if (((!in_pf || smaps)) && file_thp_enabled(vma))
- return true;
- return false;
+ return orders;
+ return 0;
}
if (vma_is_temporary_stack(vma))
- return false;
+ return 0;
/*
* THPeligible bit of smaps should show 1 for proper VMAs even
@@ -156,9 +230,9 @@ bool hugepage_vma_check(struct vm_area_struct *vma, unsigned long vm_flags,
* the first page fault.
*/
if (!vma->anon_vma)
- return (smaps || in_pf);
+ return (smaps || in_pf) ? orders : 0;
- return true;
+ return orders;
}
static bool get_huge_zero_page(void)
@@ -412,9 +486,127 @@ static const struct attribute_group hugepage_attr_group = {
.attrs = hugepage_attr,
};
+static void hugepage_exit_sysfs(struct kobject *hugepage_kobj);
+static void thpsize_release(struct kobject *kobj);
+static LIST_HEAD(thpsize_list);
+
+struct thpsize {
+ struct kobject kobj;
+ struct list_head node;
+ int order;
+};
+
+#define to_thpsize(kobj) container_of(kobj, struct thpsize, kobj)
+
+static ssize_t thpsize_enabled_show(struct kobject *kobj,
+ struct kobj_attribute *attr, char *buf)
+{
+ int order = to_thpsize(kobj)->order;
+ const char *output;
+
+ if (test_bit(order, &huge_anon_orders_always))
+ output = "[always] global madvise never";
+ else if (test_bit(order, &huge_anon_orders_global))
+ output = "always [global] madvise never";
+ else if (test_bit(order, &huge_anon_orders_madvise))
+ output = "always global [madvise] never";
+ else
+ output = "always global madvise [never]";
+
+ return sysfs_emit(buf, "%s\n", output);
+}
+
+static ssize_t thpsize_enabled_store(struct kobject *kobj,
+ struct kobj_attribute *attr,
+ const char *buf, size_t count)
+{
+ int order = to_thpsize(kobj)->order;
+ ssize_t ret = count;
+
+ if (sysfs_streq(buf, "always")) {
+ set_bit(order, &huge_anon_orders_always);
+ clear_bit(order, &huge_anon_orders_global);
+ clear_bit(order, &huge_anon_orders_madvise);
+ } else if (sysfs_streq(buf, "global")) {
+ set_bit(order, &huge_anon_orders_global);
+ clear_bit(order, &huge_anon_orders_always);
+ clear_bit(order, &huge_anon_orders_madvise);
+ } else if (sysfs_streq(buf, "madvise")) {
+ set_bit(order, &huge_anon_orders_madvise);
+ clear_bit(order, &huge_anon_orders_always);
+ clear_bit(order, &huge_anon_orders_global);
+ } else if (sysfs_streq(buf, "never")) {
+ clear_bit(order, &huge_anon_orders_always);
+ clear_bit(order, &huge_anon_orders_global);
+ clear_bit(order, &huge_anon_orders_madvise);
+ } else
+ ret = -EINVAL;
+
+ return ret;
+}
+
+static struct kobj_attribute thpsize_enabled_attr =
+ __ATTR(enabled, 0644, thpsize_enabled_show, thpsize_enabled_store);
+
+static struct attribute *thpsize_attrs[] = {
+ &thpsize_enabled_attr.attr,
+ NULL,
+};
+
+static const struct attribute_group thpsize_attr_group = {
+ .attrs = thpsize_attrs,
+};
+
+static const struct kobj_type thpsize_ktype = {
+ .release = &thpsize_release,
+ .sysfs_ops = &kobj_sysfs_ops,
+};
+
+static struct thpsize *thpsize_create(int order, struct kobject *parent)
+{
+ unsigned long size = (PAGE_SIZE << order) / SZ_1K;
+ struct thpsize *thpsize;
+ int ret;
+
+ thpsize = kzalloc(sizeof(*thpsize), GFP_KERNEL);
+ if (!thpsize)
+ return ERR_PTR(-ENOMEM);
+
+ ret = kobject_init_and_add(&thpsize->kobj, &thpsize_ktype, parent,
+ "hugepages-%lukB", size);
+ if (ret) {
+ kfree(thpsize);
+ return ERR_PTR(ret);
+ }
+
+ ret = sysfs_create_group(&thpsize->kobj, &thpsize_attr_group);
+ if (ret) {
+ kobject_put(&thpsize->kobj);
+ return ERR_PTR(ret);
+ }
+
+ thpsize->order = order;
+ return thpsize;
+}
+
+static void thpsize_release(struct kobject *kobj)
+{
+ kfree(to_thpsize(kobj));
+}
+
static int __init hugepage_init_sysfs(struct kobject **hugepage_kobj)
{
int err;
+ struct thpsize *thpsize;
+ unsigned long orders;
+ int order;
+
+ /*
+ * Default to setting PMD-sized THP to follow the global setting and
+ * disable all other sizes. powerpc's PMD_ORDER isn't a compile-time
+ * constant so we have to do this here.
+ */
+ huge_anon_orders_global = BIT(PMD_ORDER);
*hugepage_kobj = kobject_create_and_add("transparent_hugepage", mm_kobj);
if (unlikely(!*hugepage_kobj)) {
@@ -434,8 +626,24 @@ static int __init hugepage_init_sysfs(struct kobject **hugepage_kobj)
goto remove_hp_group;
}
+ orders = THP_ORDERS_ALL_ANON;
+ order = first_order(orders);
+ while (orders) {
+ thpsize = thpsize_create(order, *hugepage_kobj);
+ if (IS_ERR(thpsize)) {
+ pr_err("failed to create thpsize for order %d\n", order);
+ err = PTR_ERR(thpsize);
+ goto remove_all;
+ }
+ list_add(&thpsize->node, &thpsize_list);
+ order = next_order(&orders, order);
+ }
+
return 0;
+remove_all:
+ hugepage_exit_sysfs(*hugepage_kobj);
+ return err;
remove_hp_group:
sysfs_remove_group(*hugepage_kobj, &hugepage_attr_group);
delete_obj:
@@ -445,6 +653,13 @@ static int __init hugepage_init_sysfs(struct kobject **hugepage_kobj)
static void __init hugepage_exit_sysfs(struct kobject *hugepage_kobj)
{
+ struct thpsize *thpsize, *tmp;
+
+ list_for_each_entry_safe(thpsize, tmp, &thpsize_list, node) {
+ list_del(&thpsize->node);
+ kobject_put(&thpsize->kobj);
+ }
+
sysfs_remove_group(hugepage_kobj, &khugepaged_attr_group);
sysfs_remove_group(hugepage_kobj, &hugepage_attr_group);
kobject_put(hugepage_kobj);
@@ -811,7 +1026,7 @@ vm_fault_t do_huge_pmd_anonymous_page(struct vm_fault *vmf)
struct folio *folio;
unsigned long haddr = vmf->address & HPAGE_PMD_MASK;
- if (!transhuge_vma_suitable(vma, haddr))
+ if (!transhuge_vma_suitable(vma, haddr, BIT(PMD_ORDER)))
return VM_FAULT_FALLBACK;
if (unlikely(anon_vma_prepare(vma)))
return VM_FAULT_OOM;
@@ -446,7 +446,8 @@ void khugepaged_enter_vma(struct vm_area_struct *vma,
{
if (!test_bit(MMF_VM_HUGEPAGE, &vma->vm_mm->flags) &&
hugepage_flags_enabled()) {
- if (hugepage_vma_check(vma, vm_flags, false, false, true))
+ if (hugepage_vma_check(vma, vm_flags, false, false, true,
+ BIT(PMD_ORDER)))
__khugepaged_enter(vma->vm_mm);
}
}
@@ -922,10 +923,10 @@ static int hugepage_vma_revalidate(struct mm_struct *mm, unsigned long address,
if (!vma)
return SCAN_VMA_NULL;
- if (!transhuge_vma_suitable(vma, address))
+ if (!transhuge_vma_suitable(vma, address, BIT(PMD_ORDER)))
return SCAN_ADDRESS_RANGE;
if (!hugepage_vma_check(vma, vma->vm_flags, false, false,
- cc->is_khugepaged))
+ cc->is_khugepaged, BIT(PMD_ORDER)))
return SCAN_VMA_CHECK;
/*
* Anon VMA expected, the address may be unmapped then
@@ -1503,7 +1504,8 @@ int collapse_pte_mapped_thp(struct mm_struct *mm, unsigned long addr,
* and map it by a PMD, regardless of sysfs THP settings. As such, let's
* analogously elide sysfs THP settings here.
*/
- if (!hugepage_vma_check(vma, vma->vm_flags, false, false, false))
+ if (!hugepage_vma_check(vma, vma->vm_flags, false, false, false,
+ BIT(PMD_ORDER)))
return SCAN_VMA_CHECK;
/* Keep pmd pgtable for uffd-wp; see comment in retract_page_tables() */
@@ -2368,7 +2370,8 @@ static unsigned int khugepaged_scan_mm_slot(unsigned int pages, int *result,
progress++;
break;
}
- if (!hugepage_vma_check(vma, vma->vm_flags, false, false, true)) {
+ if (!hugepage_vma_check(vma, vma->vm_flags, false, false, true,
+ BIT(PMD_ORDER))) {
skip:
progress++;
continue;
@@ -2705,7 +2708,8 @@ int madvise_collapse(struct vm_area_struct *vma, struct vm_area_struct **prev,
*prev = vma;
- if (!hugepage_vma_check(vma, vma->vm_flags, false, false, false))
+ if (!hugepage_vma_check(vma, vma->vm_flags, false, false, false,
+ BIT(PMD_ORDER)))
return -EINVAL;
cc = kmalloc(sizeof(*cc), GFP_KERNEL);
@@ -4319,7 +4319,7 @@ vm_fault_t do_set_pmd(struct vm_fault *vmf, struct page *page)
pmd_t entry;
vm_fault_t ret = VM_FAULT_FALLBACK;
- if (!transhuge_vma_suitable(vma, haddr))
+ if (!transhuge_vma_suitable(vma, haddr, BIT(PMD_ORDER)))
return ret;
page = compound_head(page);
@@ -5117,7 +5117,7 @@ static vm_fault_t __handle_mm_fault(struct vm_area_struct *vma,
return VM_FAULT_OOM;
retry_pud:
if (pud_none(*vmf.pud) &&
- hugepage_vma_check(vma, vm_flags, false, true, true)) {
+ hugepage_vma_check(vma, vm_flags, false, true, true, BIT(PUD_ORDER))) {
ret = create_huge_pud(&vmf);
if (!(ret & VM_FAULT_FALLBACK))
return ret;
@@ -5151,7 +5151,7 @@ static vm_fault_t __handle_mm_fault(struct vm_area_struct *vma,
goto retry_pud;
if (pmd_none(*vmf.pmd) &&
- hugepage_vma_check(vma, vm_flags, false, true, true)) {
+ hugepage_vma_check(vma, vm_flags, false, true, true, BIT(PMD_ORDER))) {
ret = create_huge_pmd(&vmf);
if (!(ret & VM_FAULT_FALLBACK))
return ret;
@@ -268,7 +268,8 @@ bool page_vma_mapped_walk(struct page_vma_mapped_walk *pvmw)
* cleared *pmd but not decremented compound_mapcount().
*/
if ((pvmw->flags & PVMW_SYNC) &&
- transhuge_vma_suitable(vma, pvmw->address) &&
+ transhuge_vma_suitable(vma, pvmw->address,
+ BIT(PMD_ORDER)) &&
(pvmw->nr_pages >= HPAGE_PMD_NR)) {
spinlock_t *ptl = pmd_lock(mm, pvmw->pmd);