diff mbox series

[v1,01/10] mm: Expose clear_huge_page() unconditionally

Message ID 20230626171430.3167004-2-ryan.roberts@arm.com
State New
Headers
Series variable-order, large folios for anonymous memory |

Commit Message

Ryan Roberts June 26, 2023, 5:14 p.m. UTC 
  In preparation for extending vma_alloc_zeroed_movable_folio() to
allocate a arbitrary order folio, expose clear_huge_page()
unconditionally, so that it can be used to zero the allocated folio in
the generic implementation of vma_alloc_zeroed_movable_folio().

Signed-off-by: Ryan Roberts <ryan.roberts@arm.com>
---
 include/linux/mm.h | 3 ++-
 mm/memory.c        | 2 +-
 2 files changed, 3 insertions(+), 2 deletions(-)

Comments

Yu Zhao June 27, 2023, 1:55 a.m. UTC | #1 
On Mon, Jun 26, 2023 at 11:14 AM Ryan Roberts <ryan.roberts@arm.com> wrote:
>
> In preparation for extending vma_alloc_zeroed_movable_folio() to
> allocate a arbitrary order folio, expose clear_huge_page()
> unconditionally, so that it can be used to zero the allocated folio in
> the generic implementation of vma_alloc_zeroed_movable_folio().
>
> Signed-off-by: Ryan Roberts <ryan.roberts@arm.com>
> ---
>  include/linux/mm.h | 3 ++-
>  mm/memory.c        | 2 +-
>  2 files changed, 3 insertions(+), 2 deletions(-)
>
> diff --git a/include/linux/mm.h b/include/linux/mm.h
> index 7f1741bd870a..7e3bf45e6491 100644
> --- a/include/linux/mm.h
> +++ b/include/linux/mm.h
> @@ -3684,10 +3684,11 @@ enum mf_action_page_type {
>   */
>  extern const struct attribute_group memory_failure_attr_group;
>
> -#if defined(CONFIG_TRANSPARENT_HUGEPAGE) || defined(CONFIG_HUGETLBFS)
>  extern void clear_huge_page(struct page *page,
>                             unsigned long addr_hint,
>                             unsigned int pages_per_huge_page);
> +
> +#if defined(CONFIG_TRANSPARENT_HUGEPAGE) || defined(CONFIG_HUGETLBFS)

We might not want to depend on THP eventually. Right now, we still
have to, unless splitting is optional, which seems to contradict
06/10. (deferred_split_folio()  is a nop without THP.)
Ryan Roberts June 27, 2023, 7:21 a.m. UTC | #2 
On 27/06/2023 02:55, Yu Zhao wrote:
> On Mon, Jun 26, 2023 at 11:14 AM Ryan Roberts <ryan.roberts@arm.com> wrote:
>>
>> In preparation for extending vma_alloc_zeroed_movable_folio() to
>> allocate a arbitrary order folio, expose clear_huge_page()
>> unconditionally, so that it can be used to zero the allocated folio in
>> the generic implementation of vma_alloc_zeroed_movable_folio().
>>
>> Signed-off-by: Ryan Roberts <ryan.roberts@arm.com>
>> ---
>>  include/linux/mm.h | 3 ++-
>>  mm/memory.c        | 2 +-
>>  2 files changed, 3 insertions(+), 2 deletions(-)
>>
>> diff --git a/include/linux/mm.h b/include/linux/mm.h
>> index 7f1741bd870a..7e3bf45e6491 100644
>> --- a/include/linux/mm.h
>> +++ b/include/linux/mm.h
>> @@ -3684,10 +3684,11 @@ enum mf_action_page_type {
>>   */
>>  extern const struct attribute_group memory_failure_attr_group;
>>
>> -#if defined(CONFIG_TRANSPARENT_HUGEPAGE) || defined(CONFIG_HUGETLBFS)
>>  extern void clear_huge_page(struct page *page,
>>                             unsigned long addr_hint,
>>                             unsigned int pages_per_huge_page);
>> +
>> +#if defined(CONFIG_TRANSPARENT_HUGEPAGE) || defined(CONFIG_HUGETLBFS)
> 
> We might not want to depend on THP eventually. Right now, we still
> have to, unless splitting is optional, which seems to contradict
> 06/10. (deferred_split_folio()  is a nop without THP.)

Yes, I agree - for large anon folios to work, we depend on THP. But I don't
think that helps us here.

In the next patch, I give vma_alloc_zeroed_movable_folio() an extra `order`
parameter. So the generic/default version of the function now needs a way to
clear a compound page.

I guess I could do something like:

 static inline
 struct folio *vma_alloc_zeroed_movable_folio(struct vm_area_struct *vma,
				   unsigned long vaddr, gfp_t gfp, int order)
 {
 	struct folio *folio;

	folio = vma_alloc_folio(GFP_HIGHUSER_MOVABLE | gfp,
					order, vma, vaddr, false);
 	if (folio) {
#ifdef CONFIG_LARGE_FOLIO
		clear_huge_page(&folio->page, vaddr, 1U << order);
#else
		BUG_ON(order != 0);
		clear_user_highpage(&folio->page, vaddr);
#endif
	}

 	return folio;
 }

But that's pretty messy and there's no reason why other users might come along
that pass order != 0 and will be surprised by the BUG_ON.
Yu Zhao June 27, 2023, 8:29 a.m. UTC | #3 
On Tue, Jun 27, 2023 at 1:21 AM Ryan Roberts <ryan.roberts@arm.com> wrote:
>
> On 27/06/2023 02:55, Yu Zhao wrote:
> > On Mon, Jun 26, 2023 at 11:14 AM Ryan Roberts <ryan.roberts@arm.com> wrote:
> >>
> >> In preparation for extending vma_alloc_zeroed_movable_folio() to
> >> allocate a arbitrary order folio, expose clear_huge_page()
> >> unconditionally, so that it can be used to zero the allocated folio in
> >> the generic implementation of vma_alloc_zeroed_movable_folio().
> >>
> >> Signed-off-by: Ryan Roberts <ryan.roberts@arm.com>
> >> ---
> >>  include/linux/mm.h | 3 ++-
> >>  mm/memory.c        | 2 +-
> >>  2 files changed, 3 insertions(+), 2 deletions(-)
> >>
> >> diff --git a/include/linux/mm.h b/include/linux/mm.h
> >> index 7f1741bd870a..7e3bf45e6491 100644
> >> --- a/include/linux/mm.h
> >> +++ b/include/linux/mm.h
> >> @@ -3684,10 +3684,11 @@ enum mf_action_page_type {
> >>   */
> >>  extern const struct attribute_group memory_failure_attr_group;
> >>
> >> -#if defined(CONFIG_TRANSPARENT_HUGEPAGE) || defined(CONFIG_HUGETLBFS)
> >>  extern void clear_huge_page(struct page *page,
> >>                             unsigned long addr_hint,
> >>                             unsigned int pages_per_huge_page);
> >> +
> >> +#if defined(CONFIG_TRANSPARENT_HUGEPAGE) || defined(CONFIG_HUGETLBFS)
> >
> > We might not want to depend on THP eventually. Right now, we still
> > have to, unless splitting is optional, which seems to contradict
> > 06/10. (deferred_split_folio()  is a nop without THP.)
>
> Yes, I agree - for large anon folios to work, we depend on THP. But I don't
> think that helps us here.
>
> In the next patch, I give vma_alloc_zeroed_movable_folio() an extra `order`
> parameter. So the generic/default version of the function now needs a way to
> clear a compound page.
>
> I guess I could do something like:
>
>  static inline
>  struct folio *vma_alloc_zeroed_movable_folio(struct vm_area_struct *vma,
>                                    unsigned long vaddr, gfp_t gfp, int order)
>  {
>         struct folio *folio;
>
>         folio = vma_alloc_folio(GFP_HIGHUSER_MOVABLE | gfp,
>                                         order, vma, vaddr, false);
>         if (folio) {
> #ifdef CONFIG_LARGE_FOLIO
>                 clear_huge_page(&folio->page, vaddr, 1U << order);
> #else
>                 BUG_ON(order != 0);
>                 clear_user_highpage(&folio->page, vaddr);
> #endif
>         }
>
>         return folio;
>  }
>
> But that's pretty messy and there's no reason why other users might come along
> that pass order != 0 and will be surprised by the BUG_ON.

#ifdef CONFIG_LARGE_ANON_FOLIO // depends on CONFIG_TRANSPARENT_HUGE_PAGE
struct folio *alloc_anon_folio(struct vm_area_struct *vma, unsigned
long vaddr, int order)
{
  // how do_huge_pmd_anonymous_page() allocs and clears
  vma_alloc_folio(..., *true*);
}
#else
#define alloc_anon_folio(vma, addr, order)
vma_alloc_zeroed_movable_folio(vma, addr)
#endif
Ryan Roberts June 27, 2023, 9:41 a.m. UTC | #4 
On 27/06/2023 09:29, Yu Zhao wrote:
> On Tue, Jun 27, 2023 at 1:21 AM Ryan Roberts <ryan.roberts@arm.com> wrote:
>>
>> On 27/06/2023 02:55, Yu Zhao wrote:
>>> On Mon, Jun 26, 2023 at 11:14 AM Ryan Roberts <ryan.roberts@arm.com> wrote:
>>>>
>>>> In preparation for extending vma_alloc_zeroed_movable_folio() to
>>>> allocate a arbitrary order folio, expose clear_huge_page()
>>>> unconditionally, so that it can be used to zero the allocated folio in
>>>> the generic implementation of vma_alloc_zeroed_movable_folio().
>>>>
>>>> Signed-off-by: Ryan Roberts <ryan.roberts@arm.com>
>>>> ---
>>>>  include/linux/mm.h | 3 ++-
>>>>  mm/memory.c        | 2 +-
>>>>  2 files changed, 3 insertions(+), 2 deletions(-)
>>>>
>>>> diff --git a/include/linux/mm.h b/include/linux/mm.h
>>>> index 7f1741bd870a..7e3bf45e6491 100644
>>>> --- a/include/linux/mm.h
>>>> +++ b/include/linux/mm.h
>>>> @@ -3684,10 +3684,11 @@ enum mf_action_page_type {
>>>>   */
>>>>  extern const struct attribute_group memory_failure_attr_group;
>>>>
>>>> -#if defined(CONFIG_TRANSPARENT_HUGEPAGE) || defined(CONFIG_HUGETLBFS)
>>>>  extern void clear_huge_page(struct page *page,
>>>>                             unsigned long addr_hint,
>>>>                             unsigned int pages_per_huge_page);
>>>> +
>>>> +#if defined(CONFIG_TRANSPARENT_HUGEPAGE) || defined(CONFIG_HUGETLBFS)
>>>
>>> We might not want to depend on THP eventually. Right now, we still
>>> have to, unless splitting is optional, which seems to contradict
>>> 06/10. (deferred_split_folio()  is a nop without THP.)
>>
>> Yes, I agree - for large anon folios to work, we depend on THP. But I don't
>> think that helps us here.
>>
>> In the next patch, I give vma_alloc_zeroed_movable_folio() an extra `order`
>> parameter. So the generic/default version of the function now needs a way to
>> clear a compound page.
>>
>> I guess I could do something like:
>>
>>  static inline
>>  struct folio *vma_alloc_zeroed_movable_folio(struct vm_area_struct *vma,
>>                                    unsigned long vaddr, gfp_t gfp, int order)
>>  {
>>         struct folio *folio;
>>
>>         folio = vma_alloc_folio(GFP_HIGHUSER_MOVABLE | gfp,
>>                                         order, vma, vaddr, false);
>>         if (folio) {
>> #ifdef CONFIG_LARGE_FOLIO
>>                 clear_huge_page(&folio->page, vaddr, 1U << order);
>> #else
>>                 BUG_ON(order != 0);
>>                 clear_user_highpage(&folio->page, vaddr);
>> #endif
>>         }
>>
>>         return folio;
>>  }
>>
>> But that's pretty messy and there's no reason why other users might come along
>> that pass order != 0 and will be surprised by the BUG_ON.
> 
> #ifdef CONFIG_LARGE_ANON_FOLIO // depends on CONFIG_TRANSPARENT_HUGE_PAGE
> struct folio *alloc_anon_folio(struct vm_area_struct *vma, unsigned
> long vaddr, int order)
> {
>   // how do_huge_pmd_anonymous_page() allocs and clears
>   vma_alloc_folio(..., *true*);

This controls the mem allocation policy (see mempolicy.c::vma_alloc_folio()) not
clearing. Clearing is done in __do_huge_pmd_anonymous_page():

  clear_huge_page(page, vmf->address, HPAGE_PMD_NR);

> }
> #else
> #define alloc_anon_folio(vma, addr, order)
> vma_alloc_zeroed_movable_folio(vma, addr)
> #endif

Sorry I don't get this at all... If you are suggesting to bypass
vma_alloc_zeroed_movable_folio() entirely for the LARGE_ANON_FOLIO case, I don't
think that works because the arch code adds its own gfp flags there. For
example, arm64 adds __GFP_ZEROTAGS for VM_MTE VMAs.

Perhaps we can do away with an arch-owned vma_alloc_zeroed_movable_folio() and
replace it with a new arch_get_zeroed_movable_gfp_flags() then
alloc_anon_folio() add in those flags?

But I still think the cleanest, simplest change is just to unconditionally
expose clear_huge_page() as I've done it.
Yu Zhao June 27, 2023, 6:26 p.m. UTC | #5 
On Tue, Jun 27, 2023 at 3:41 AM Ryan Roberts <ryan.roberts@arm.com> wrote:
>
> On 27/06/2023 09:29, Yu Zhao wrote:
> > On Tue, Jun 27, 2023 at 1:21 AM Ryan Roberts <ryan.roberts@arm.com> wrote:
> >>
> >> On 27/06/2023 02:55, Yu Zhao wrote:
> >>> On Mon, Jun 26, 2023 at 11:14 AM Ryan Roberts <ryan.roberts@arm.com> wrote:
> >>>>
> >>>> In preparation for extending vma_alloc_zeroed_movable_folio() to
> >>>> allocate a arbitrary order folio, expose clear_huge_page()
> >>>> unconditionally, so that it can be used to zero the allocated folio in
> >>>> the generic implementation of vma_alloc_zeroed_movable_folio().
> >>>>
> >>>> Signed-off-by: Ryan Roberts <ryan.roberts@arm.com>
> >>>> ---
> >>>>  include/linux/mm.h | 3 ++-
> >>>>  mm/memory.c        | 2 +-
> >>>>  2 files changed, 3 insertions(+), 2 deletions(-)
> >>>>
> >>>> diff --git a/include/linux/mm.h b/include/linux/mm.h
> >>>> index 7f1741bd870a..7e3bf45e6491 100644
> >>>> --- a/include/linux/mm.h
> >>>> +++ b/include/linux/mm.h
> >>>> @@ -3684,10 +3684,11 @@ enum mf_action_page_type {
> >>>>   */
> >>>>  extern const struct attribute_group memory_failure_attr_group;
> >>>>
> >>>> -#if defined(CONFIG_TRANSPARENT_HUGEPAGE) || defined(CONFIG_HUGETLBFS)
> >>>>  extern void clear_huge_page(struct page *page,
> >>>>                             unsigned long addr_hint,
> >>>>                             unsigned int pages_per_huge_page);
> >>>> +
> >>>> +#if defined(CONFIG_TRANSPARENT_HUGEPAGE) || defined(CONFIG_HUGETLBFS)
> >>>
> >>> We might not want to depend on THP eventually. Right now, we still
> >>> have to, unless splitting is optional, which seems to contradict
> >>> 06/10. (deferred_split_folio()  is a nop without THP.)
> >>
> >> Yes, I agree - for large anon folios to work, we depend on THP. But I don't
> >> think that helps us here.
> >>
> >> In the next patch, I give vma_alloc_zeroed_movable_folio() an extra `order`
> >> parameter. So the generic/default version of the function now needs a way to
> >> clear a compound page.
> >>
> >> I guess I could do something like:
> >>
> >>  static inline
> >>  struct folio *vma_alloc_zeroed_movable_folio(struct vm_area_struct *vma,
> >>                                    unsigned long vaddr, gfp_t gfp, int order)
> >>  {
> >>         struct folio *folio;
> >>
> >>         folio = vma_alloc_folio(GFP_HIGHUSER_MOVABLE | gfp,
> >>                                         order, vma, vaddr, false);
> >>         if (folio) {
> >> #ifdef CONFIG_LARGE_FOLIO
> >>                 clear_huge_page(&folio->page, vaddr, 1U << order);
> >> #else
> >>                 BUG_ON(order != 0);
> >>                 clear_user_highpage(&folio->page, vaddr);
> >> #endif
> >>         }
> >>
> >>         return folio;
> >>  }
> >>
> >> But that's pretty messy and there's no reason why other users might come along
> >> that pass order != 0 and will be surprised by the BUG_ON.
> >
> > #ifdef CONFIG_LARGE_ANON_FOLIO // depends on CONFIG_TRANSPARENT_HUGE_PAGE
> > struct folio *alloc_anon_folio(struct vm_area_struct *vma, unsigned
> > long vaddr, int order)
> > {
> >   // how do_huge_pmd_anonymous_page() allocs and clears
> >   vma_alloc_folio(..., *true*);
>
> This controls the mem allocation policy (see mempolicy.c::vma_alloc_folio()) not
> clearing. Clearing is done in __do_huge_pmd_anonymous_page():
>
>   clear_huge_page(page, vmf->address, HPAGE_PMD_NR);

Sorry for rushing this previously. This is what I meant. The #ifdef
makes it safe to use clear_huge_page() without 01/10. I highlighted
the last parameter to vma_alloc_folio() only because it's different
from what you chose (not implying it clears the folio).

> > }
> > #else
> > #define alloc_anon_folio(vma, addr, order)
> > vma_alloc_zeroed_movable_folio(vma, addr)
> > #endif
>
> Sorry I don't get this at all... If you are suggesting to bypass
> vma_alloc_zeroed_movable_folio() entirely for the LARGE_ANON_FOLIO case

Correct.

> I don't
> think that works because the arch code adds its own gfp flags there. For
> example, arm64 adds __GFP_ZEROTAGS for VM_MTE VMAs.

I think it's the opposite: it should be safer to reuse the THP code because
1. It's an existing case that has been working for PMD_ORDER folios
mapped by PTEs, and it's an arch-independent API which would be easier
to review.
2. Use vma_alloc_zeroed_movable_folio() for large folios is a *new*
case. It's an arch-*dependent* API which I have no idea what VM_MTE
does (should do) to large folios and don't plan to answer that for
now.

> Perhaps we can do away with an arch-owned vma_alloc_zeroed_movable_folio() and
> replace it with a new arch_get_zeroed_movable_gfp_flags() then
> alloc_anon_folio() add in those flags?
>
> But I still think the cleanest, simplest change is just to unconditionally
> expose clear_huge_page() as I've done it.

The fundamental choice there as I see it is to whether the first step
of large anon folios should lean toward the THP code base or the base
page code base (I'm a big fan of the answer "Neither -- we should
create something entirely new instead"). My POV is that the THP code
base would allow us to move faster, since it's proven to work for a
very similar case (PMD_ORDER folios mapped by PTEs).
Ryan Roberts June 28, 2023, 10:56 a.m. UTC | #6 
On 27/06/2023 19:26, Yu Zhao wrote:
> On Tue, Jun 27, 2023 at 3:41 AM Ryan Roberts <ryan.roberts@arm.com> wrote:
>>
>> On 27/06/2023 09:29, Yu Zhao wrote:
>>> On Tue, Jun 27, 2023 at 1:21 AM Ryan Roberts <ryan.roberts@arm.com> wrote:
>>>>
>>>> On 27/06/2023 02:55, Yu Zhao wrote:
>>>>> On Mon, Jun 26, 2023 at 11:14 AM Ryan Roberts <ryan.roberts@arm.com> wrote:
>>>>>>
>>>>>> In preparation for extending vma_alloc_zeroed_movable_folio() to
>>>>>> allocate a arbitrary order folio, expose clear_huge_page()
>>>>>> unconditionally, so that it can be used to zero the allocated folio in
>>>>>> the generic implementation of vma_alloc_zeroed_movable_folio().
>>>>>>
>>>>>> Signed-off-by: Ryan Roberts <ryan.roberts@arm.com>
>>>>>> ---
>>>>>>  include/linux/mm.h | 3 ++-
>>>>>>  mm/memory.c        | 2 +-
>>>>>>  2 files changed, 3 insertions(+), 2 deletions(-)
>>>>>>
>>>>>> diff --git a/include/linux/mm.h b/include/linux/mm.h
>>>>>> index 7f1741bd870a..7e3bf45e6491 100644
>>>>>> --- a/include/linux/mm.h
>>>>>> +++ b/include/linux/mm.h
>>>>>> @@ -3684,10 +3684,11 @@ enum mf_action_page_type {
>>>>>>   */
>>>>>>  extern const struct attribute_group memory_failure_attr_group;
>>>>>>
>>>>>> -#if defined(CONFIG_TRANSPARENT_HUGEPAGE) || defined(CONFIG_HUGETLBFS)
>>>>>>  extern void clear_huge_page(struct page *page,
>>>>>>                             unsigned long addr_hint,
>>>>>>                             unsigned int pages_per_huge_page);
>>>>>> +
>>>>>> +#if defined(CONFIG_TRANSPARENT_HUGEPAGE) || defined(CONFIG_HUGETLBFS)
>>>>>
>>>>> We might not want to depend on THP eventually. Right now, we still
>>>>> have to, unless splitting is optional, which seems to contradict
>>>>> 06/10. (deferred_split_folio()  is a nop without THP.)
>>>>
>>>> Yes, I agree - for large anon folios to work, we depend on THP. But I don't
>>>> think that helps us here.
>>>>
>>>> In the next patch, I give vma_alloc_zeroed_movable_folio() an extra `order`
>>>> parameter. So the generic/default version of the function now needs a way to
>>>> clear a compound page.
>>>>
>>>> I guess I could do something like:
>>>>
>>>>  static inline
>>>>  struct folio *vma_alloc_zeroed_movable_folio(struct vm_area_struct *vma,
>>>>                                    unsigned long vaddr, gfp_t gfp, int order)
>>>>  {
>>>>         struct folio *folio;
>>>>
>>>>         folio = vma_alloc_folio(GFP_HIGHUSER_MOVABLE | gfp,
>>>>                                         order, vma, vaddr, false);
>>>>         if (folio) {
>>>> #ifdef CONFIG_LARGE_FOLIO
>>>>                 clear_huge_page(&folio->page, vaddr, 1U << order);
>>>> #else
>>>>                 BUG_ON(order != 0);
>>>>                 clear_user_highpage(&folio->page, vaddr);
>>>> #endif
>>>>         }
>>>>
>>>>         return folio;
>>>>  }
>>>>
>>>> But that's pretty messy and there's no reason why other users might come along
>>>> that pass order != 0 and will be surprised by the BUG_ON.
>>>
>>> #ifdef CONFIG_LARGE_ANON_FOLIO // depends on CONFIG_TRANSPARENT_HUGE_PAGE
>>> struct folio *alloc_anon_folio(struct vm_area_struct *vma, unsigned
>>> long vaddr, int order)
>>> {
>>>   // how do_huge_pmd_anonymous_page() allocs and clears
>>>   vma_alloc_folio(..., *true*);
>>
>> This controls the mem allocation policy (see mempolicy.c::vma_alloc_folio()) not
>> clearing. Clearing is done in __do_huge_pmd_anonymous_page():
>>
>>   clear_huge_page(page, vmf->address, HPAGE_PMD_NR);
> 
> Sorry for rushing this previously. This is what I meant. The #ifdef
> makes it safe to use clear_huge_page() without 01/10. I highlighted
> the last parameter to vma_alloc_folio() only because it's different
> from what you chose (not implying it clears the folio).>
>>> }
>>> #else
>>> #define alloc_anon_folio(vma, addr, order)
>>> vma_alloc_zeroed_movable_folio(vma, addr)
>>> #endif
>>
>> Sorry I don't get this at all... If you are suggesting to bypass
>> vma_alloc_zeroed_movable_folio() entirely for the LARGE_ANON_FOLIO case
> 
> Correct.
> 
>> I don't
>> think that works because the arch code adds its own gfp flags there. For
>> example, arm64 adds __GFP_ZEROTAGS for VM_MTE VMAs.
> 
> I think it's the opposite: it should be safer to reuse the THP code because
> 1. It's an existing case that has been working for PMD_ORDER folios
> mapped by PTEs, and it's an arch-independent API which would be easier
> to review.
> 2. Use vma_alloc_zeroed_movable_folio() for large folios is a *new*
> case. It's an arch-*dependent* API which I have no idea what VM_MTE
> does (should do) to large folios and don't plan to answer that for
> now.

I've done some archaology on this now, and convinced myself that your suggestion
is a good one - sorry for doubting it!

If you are interested here are the details: Only arm64 and ia64 do something
non-standard in vma_alloc_zeroed_movable_folio(). ia64 flushes the dcache for
the folio - but given it does not support THP this is not a problem for the THP
path. arm64 adds the __GFP_ZEROTAGS flag which means that the MTE tags will be
zeroed at the same time as the page is zeroed. This is a perf optimization - if
its not performed then it will be done at set_pte_at(), which is how this works
for the THP path.

So on that basis, I agree we can use your proposed alloc_anon_folio() approach.
arm64 will lose the MTE optimization but that can be added back later if needed.
So no need to unconditionally expose clear_huge_page() and no need to modify all
the arch vma_alloc_zeroed_movable_folio() implementations.

Thanks,
Ryan


> 
>> Perhaps we can do away with an arch-owned vma_alloc_zeroed_movable_folio() and
>> replace it with a new arch_get_zeroed_movable_gfp_flags() then
>> alloc_anon_folio() add in those flags?
>>
>> But I still think the cleanest, simplest change is just to unconditionally
>> expose clear_huge_page() as I've done it.
> 
> The fundamental choice there as I see it is to whether the first step
> of large anon folios should lean toward the THP code base or the base
> page code base (I'm a big fan of the answer "Neither -- we should
> create something entirely new instead"). My POV is that the THP code
> base would allow us to move faster, since it's proven to work for a
> very similar case (PMD_ORDER folios mapped by PTEs).
diff mbox series

Patch

diff --git a/include/linux/mm.h b/include/linux/mm.h
index 7f1741bd870a..7e3bf45e6491 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -3684,10 +3684,11 @@  enum mf_action_page_type {
  */
 extern const struct attribute_group memory_failure_attr_group;
 
-#if defined(CONFIG_TRANSPARENT_HUGEPAGE) || defined(CONFIG_HUGETLBFS)
 extern void clear_huge_page(struct page *page,
 			    unsigned long addr_hint,
 			    unsigned int pages_per_huge_page);
+
+#if defined(CONFIG_TRANSPARENT_HUGEPAGE) || defined(CONFIG_HUGETLBFS)
 int copy_user_large_folio(struct folio *dst, struct folio *src,
 			  unsigned long addr_hint,
 			  struct vm_area_struct *vma);
diff --git a/mm/memory.c b/mm/memory.c
index fb30f7523550..3d4ea668c4d1 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -5741,7 +5741,6 @@  void __might_fault(const char *file, int line)
 EXPORT_SYMBOL(__might_fault);
 #endif
 
-#if defined(CONFIG_TRANSPARENT_HUGEPAGE) || defined(CONFIG_HUGETLBFS)
 /*
  * Process all subpages of the specified huge page with the specified
  * operation.  The target subpage will be processed last to keep its
@@ -5839,6 +5838,7 @@  void clear_huge_page(struct page *page,
 	process_huge_page(addr_hint, pages_per_huge_page, clear_subpage, page);
 }
 
+#if defined(CONFIG_TRANSPARENT_HUGEPAGE) || defined(CONFIG_HUGETLBFS)
 static int copy_user_gigantic_page(struct folio *dst, struct folio *src,
 				     unsigned long addr,
 				     struct vm_area_struct *vma,