[v8,2/3] cachestat: implement cachestat syscall
Commit Message
There is currently no good way to query the page cache state of large
file sets and directory trees. There is mincore(), but it scales poorly:
the kernel writes out a lot of bitmap data that userspace has to
aggregate, when the user really doesn not care about per-page
information in that case. The user also needs to mmap and unmap each
file as it goes along, which can be quite slow as well.
This patch implements a new syscall that queries cache state of a file
and summarizes the number of cached pages, number of dirty pages, number
of pages marked for writeback, number of (recently) evicted pages, etc.
in a given range.
NAME
cachestat - query the page cache statistics of a file.
SYNOPSIS
#include <sys/mman.h>
struct cachestat {
__u64 nr_cache;
__u64 nr_dirty;
__u64 nr_writeback;
__u64 nr_evicted;
__u64 nr_recently_evicted;
};
int cachestat(unsigned int fd, off_t off, size_t len,
unsigned int cstat_version, struct cachestat *cstat,
unsigned int flags);
DESCRIPTION
cachestat() queries the number of cached pages, number of dirty
pages, number of pages marked for writeback, number of evicted
pages, number of recently evicted pages, in the bytes range given by
`off` and `len`.
An evicted page is a page that is previously in the page cache but
has been evicted since. A page is recently evicted if its last
eviction was recent enough that its reentry to the cache would
indicate that it is actively being used by the system, and that
there is memory pressure on the system.
These values are returned in a cachestat struct, whose address is
given by the `cstat` argument.
The `off` and `len` arguments must be non-negative integers. If
`len` > 0, the queried range is [`off`, `off` + `len`]. If `len` ==
0, we will query in the range from `off` to the end of the file.
`cstat_version` is an unsigned integer indicating the specific
version of the cachestat struct. It must be at least 1, and does
not exceed the latest version number (which is currently 1). For
now, user should just pass 1.
The `flags` argument is unused for now, but is included for future
extensibility. User should pass 0 (i.e no flag specified).
RETURN VALUE
On success, cachestat returns 0. On error, -1 is returned, and errno
is set to indicate the error.
ERRORS
EFAULT cstat points to an invalid address.
EINVAL invalid `cstat_version` or `flags`
EBADF invalid file descriptor.
Signed-off-by: Nhat Pham <nphamcs@gmail.com>
---
arch/alpha/kernel/syscalls/syscall.tbl | 1 +
arch/arm/tools/syscall.tbl | 1 +
arch/ia64/kernel/syscalls/syscall.tbl | 1 +
arch/m68k/kernel/syscalls/syscall.tbl | 1 +
arch/microblaze/kernel/syscalls/syscall.tbl | 1 +
arch/mips/kernel/syscalls/syscall_n32.tbl | 1 +
arch/mips/kernel/syscalls/syscall_n64.tbl | 1 +
arch/mips/kernel/syscalls/syscall_o32.tbl | 1 +
arch/parisc/kernel/syscalls/syscall.tbl | 1 +
arch/powerpc/kernel/syscalls/syscall.tbl | 1 +
arch/s390/kernel/syscalls/syscall.tbl | 1 +
arch/sh/kernel/syscalls/syscall.tbl | 1 +
arch/sparc/kernel/syscalls/syscall.tbl | 1 +
arch/x86/entry/syscalls/syscall_32.tbl | 1 +
arch/x86/entry/syscalls/syscall_64.tbl | 1 +
arch/xtensa/kernel/syscalls/syscall.tbl | 1 +
include/linux/fs.h | 3 +
include/linux/syscalls.h | 4 +
include/uapi/asm-generic/unistd.h | 5 +-
include/uapi/linux/mman.h | 9 ++
init/Kconfig | 10 ++
kernel/sys_ni.c | 1 +
mm/filemap.c | 154 ++++++++++++++++++++
23 files changed, 201 insertions(+), 1 deletion(-)
Comments
On Thu, Jan 26, 2023, at 18:53, Nhat Pham wrote:
>
> SYNOPSIS
> #include <sys/mman.h>
>
> struct cachestat {
> __u64 nr_cache;
> __u64 nr_dirty;
> __u64 nr_writeback;
> __u64 nr_evicted;
> __u64 nr_recently_evicted;
> };
>
> int cachestat(unsigned int fd, off_t off, size_t len,
> unsigned int cstat_version, struct cachestat *cstat,
> unsigned int flags);
Is this "off_t off" argument intentionally limited to the old
32-bit type on 32-bit architectures? Unfortunately I fear
there are no good options to pass an offset here:
- if you make it a 32-bit type, this breaks calling it from
normal userspace that defines off_t as a 64-bit type
- if you change it to a 64-bit loff_t, there are three
separate calling conventions for 64-bit, 32-bit with
aligned register pairs and other 32-bit, plus you
exceed the usual limit of six system call arguments
A separate problem may be the cstat_version argument, usually
we don't use interface versions but instead use a new
system call number if something changes in an incompatible
way.
Arnd
On Fri, Jan 27, 2023 at 04:46:38PM +0100, Arnd Bergmann wrote:
> On Thu, Jan 26, 2023, at 18:53, Nhat Pham wrote:
> >
> > SYNOPSIS
> > #include <sys/mman.h>
> >
> > struct cachestat {
> > __u64 nr_cache;
> > __u64 nr_dirty;
> > __u64 nr_writeback;
> > __u64 nr_evicted;
> > __u64 nr_recently_evicted;
> > };
> >
> > int cachestat(unsigned int fd, off_t off, size_t len,
> > unsigned int cstat_version, struct cachestat *cstat,
> > unsigned int flags);
>
> Is this "off_t off" argument intentionally limited to the old
> 32-bit type on 32-bit architectures? Unfortunately I fear
> there are no good options to pass an offset here:
>
> - if you make it a 32-bit type, this breaks calling it from
> normal userspace that defines off_t as a 64-bit type
>
> - if you change it to a 64-bit loff_t, there are three
> separate calling conventions for 64-bit, 32-bit with
> aligned register pairs and other 32-bit, plus you
> exceed the usual limit of six system call arguments
That's a good point, thanks for raising it, Arnd.
> A separate problem may be the cstat_version argument, usually
> we don't use interface versions but instead use a new
> system call number if something changes in an incompatible
> way.
I suppose from a userspace POV, a version argument vs calling a
separate syscall doesn't make much of a difference. So going with
loff_t and dropping cstat_version seems like a sensible way forward.
As an added bonus, versioning the syscall itself means the signature
can change in v2. This allows dropping the unused flags arg for now.
That would leave it at:
int cachestat(unsigned int, loff_t, size_t len, struct cachestat *cstat);
and should we ever require extensions - new fields, flags - they would
come through a new cachestat2().
Would anybody have objections to that?
On Fri, Jan 27, 2023, at 20:46, Johannes Weiner wrote:
> On Fri, Jan 27, 2023 at 04:46:38PM +0100, Arnd Bergmann wrote:
>>
>> - if you make it a 32-bit type, this breaks calling it from
>> normal userspace that defines off_t as a 64-bit type
>>
>> - if you change it to a 64-bit loff_t, there are three
>> separate calling conventions for 64-bit, 32-bit with
>> aligned register pairs and other 32-bit, plus you
>> exceed the usual limit of six system call arguments
>
> That's a good point, thanks for raising it, Arnd.
>
>> A separate problem may be the cstat_version argument, usually
>> we don't use interface versions but instead use a new
>> system call number if something changes in an incompatible
>> way.
>
> I suppose from a userspace POV, a version argument vs calling a
> separate syscall doesn't make much of a difference. So going with
> loff_t and dropping cstat_version seems like a sensible way forward.
>
> As an added bonus, versioning the syscall itself means the signature
> can change in v2. This allows dropping the unused flags arg for now.
>
> That would leave it at:
>
> int cachestat(unsigned int, loff_t, size_t len, struct cachestat *cstat);
There is still a problem of incompatible calling conventions:
on architectures that require even/odd register pairs, this would
end up like
int cachestat(unsigned int, long unused, u32 off_low, u32 off_high,
size_t len, struct cachestat *cstat);
A more portable way to do this would be to pass the offset by
reference, but that makes it a bit awkward in userspace.
Or the arguments could be rearranged to put the low/high argument
pair first/second, third/fourth or fifth/sixth argument, at least
on the kernel ABI to avoid having another situation like
sys_arm_fadvise64_64.
> and should we ever require extensions - new fields, flags - they would
> come through a new cachestat2().
>
> Would anybody have objections to that?
If there is room for another argument, I would keep the 'flags'
as a way for extending in a compatible way, that is pretty standard
now, just not flags plus version.
Arnd
Hi Nhat,
Thank you for the patch! Perhaps something to improve:
[auto build test WARNING on 1440f576022887004f719883acb094e7e0dd4944]
url: https://github.com/intel-lab-lkp/linux/commits/Nhat-Pham/workingset-refactor-LRU-refault-to-expose-refault-recency-check/20230128-171134
base: 1440f576022887004f719883acb094e7e0dd4944
patch link: https://lore.kernel.org/r/20230126175356.1582123-3-nphamcs%40gmail.com
patch subject: [PATCH v8 2/3] cachestat: implement cachestat syscall
config: s390-randconfig-s051-20230129 (https://download.01.org/0day-ci/archive/20230129/202301292044.JVAnbg9W-lkp@intel.com/config)
compiler: s390-linux-gcc (GCC) 12.1.0
reproduce:
wget https://raw.githubusercontent.com/intel/lkp-tests/master/sbin/make.cross -O ~/bin/make.cross
chmod +x ~/bin/make.cross
# apt-get install sparse
# sparse version: v0.6.4-39-gce1a6720-dirty
# https://github.com/intel-lab-lkp/linux/commit/a05ffdcecfe9ac147066fb8472e6fb75491d0eed
git remote add linux-review https://github.com/intel-lab-lkp/linux
git fetch --no-tags linux-review Nhat-Pham/workingset-refactor-LRU-refault-to-expose-refault-recency-check/20230128-171134
git checkout a05ffdcecfe9ac147066fb8472e6fb75491d0eed
# save the config file
mkdir build_dir && cp config build_dir/.config
COMPILER_INSTALL_PATH=$HOME/0day COMPILER=gcc-12.1.0 make.cross C=1 CF='-fdiagnostic-prefix -D__CHECK_ENDIAN__' O=build_dir ARCH=s390 olddefconfig
COMPILER_INSTALL_PATH=$HOME/0day COMPILER=gcc-12.1.0 make.cross C=1 CF='-fdiagnostic-prefix -D__CHECK_ENDIAN__' O=build_dir ARCH=s390 SHELL=/bin/bash
If you fix the issue, kindly add following tag where applicable
| Reported-by: kernel test robot <lkp@intel.com>
sparse warnings: (new ones prefixed by >>)
>> mm/filemap.c:4075:1: sparse: sparse: Using plain integer as NULL pointer
>> mm/filemap.c:4075:1: sparse: sparse: Using plain integer as NULL pointer
mm/filemap.c:1416:17: sparse: sparse: context imbalance in 'migration_entry_wait_on_locked' - unexpected unlock
vim +4075 mm/filemap.c
4037
4038 #ifdef CONFIG_CACHESTAT_SYSCALL
4039 /*
4040 * The cachestat(5) system call.
4041 *
4042 * cachestat() returns the page cache statistics of a file in the
4043 * bytes range specified by `off` and `len`: number of cached pages,
4044 * number of dirty pages, number of pages marked for writeback,
4045 * number of evicted pages, and number of recently evicted pages.
4046 *
4047 * An evicted page is a page that is previously in the page cache
4048 * but has been evicted since. A page is recently evicted if its last
4049 * eviction was recent enough that its reentry to the cache would
4050 * indicate that it is actively being used by the system, and that
4051 * there is memory pressure on the system.
4052 *
4053 * `off` and `len` must be non-negative integers. If `len` > 0,
4054 * the queried range is [`off`, `off` + `len`]. If `len` == 0,
4055 * we will query in the range from `off` to the end of the file.
4056 *
4057 * `cstat_version` is an unsigned integer indicating the specific version
4058 * of the cachestat struct. It must be at least 1, and does not exceed the
4059 * latest version number (which is currently 1). For now, user should
4060 * just pass 1.
4061 *
4062 * The `flags` argument is unused for now, but is included for future
4063 * extensibility. User should pass 0 (i.e no flag specified).
4064 *
4065 * Because the status of a page can change after cachestat() checks it
4066 * but before it returns to the application, the returned values may
4067 * contain stale information.
4068 *
4069 * return values:
4070 * zero - success
4071 * -EFAULT - cstat points to an illegal address
4072 * -EINVAL - invalid arguments
4073 * -EBADF - invalid file descriptor
4074 */
> 4075 SYSCALL_DEFINE6(cachestat, unsigned int, fd, off_t, off, size_t, len,
@@ -490,3 +490,4 @@
558 common process_mrelease sys_process_mrelease
559 common futex_waitv sys_futex_waitv
560 common set_mempolicy_home_node sys_ni_syscall
+561 common cachestat sys_cachestat
@@ -464,3 +464,4 @@
448 common process_mrelease sys_process_mrelease
449 common futex_waitv sys_futex_waitv
450 common set_mempolicy_home_node sys_set_mempolicy_home_node
+451 common cachestat sys_cachestat
@@ -371,3 +371,4 @@
448 common process_mrelease sys_process_mrelease
449 common futex_waitv sys_futex_waitv
450 common set_mempolicy_home_node sys_set_mempolicy_home_node
+451 common cachestat sys_cachestat
@@ -450,3 +450,4 @@
448 common process_mrelease sys_process_mrelease
449 common futex_waitv sys_futex_waitv
450 common set_mempolicy_home_node sys_set_mempolicy_home_node
+451 common cachestat sys_cachestat
@@ -456,3 +456,4 @@
448 common process_mrelease sys_process_mrelease
449 common futex_waitv sys_futex_waitv
450 common set_mempolicy_home_node sys_set_mempolicy_home_node
+451 common cachestat sys_cachestat
@@ -389,3 +389,4 @@
448 n32 process_mrelease sys_process_mrelease
449 n32 futex_waitv sys_futex_waitv
450 n32 set_mempolicy_home_node sys_set_mempolicy_home_node
+451 n32 cachestat sys_cachestat
@@ -365,3 +365,4 @@
448 n64 process_mrelease sys_process_mrelease
449 n64 futex_waitv sys_futex_waitv
450 common set_mempolicy_home_node sys_set_mempolicy_home_node
+451 n64 cachestat sys_cachestat
@@ -438,3 +438,4 @@
448 o32 process_mrelease sys_process_mrelease
449 o32 futex_waitv sys_futex_waitv
450 o32 set_mempolicy_home_node sys_set_mempolicy_home_node
+451 o32 cachestat sys_cachestat
@@ -448,3 +448,4 @@
448 common process_mrelease sys_process_mrelease
449 common futex_waitv sys_futex_waitv
450 common set_mempolicy_home_node sys_set_mempolicy_home_node
+451 common cachestat sys_cachestat
@@ -530,3 +530,4 @@
448 common process_mrelease sys_process_mrelease
449 common futex_waitv sys_futex_waitv
450 nospu set_mempolicy_home_node sys_set_mempolicy_home_node
+451 common cachestat sys_cachestat
@@ -453,3 +453,4 @@
448 common process_mrelease sys_process_mrelease sys_process_mrelease
449 common futex_waitv sys_futex_waitv sys_futex_waitv
450 common set_mempolicy_home_node sys_set_mempolicy_home_node sys_set_mempolicy_home_node
+451 common cachestat sys_cachestat sys_cachestat
@@ -453,3 +453,4 @@
448 common process_mrelease sys_process_mrelease
449 common futex_waitv sys_futex_waitv
450 common set_mempolicy_home_node sys_set_mempolicy_home_node
+451 common cachestat sys_cachestat
@@ -496,3 +496,4 @@
448 common process_mrelease sys_process_mrelease
449 common futex_waitv sys_futex_waitv
450 common set_mempolicy_home_node sys_set_mempolicy_home_node
+451 common cachestat sys_cachestat
@@ -455,3 +455,4 @@
448 i386 process_mrelease sys_process_mrelease
449 i386 futex_waitv sys_futex_waitv
450 i386 set_mempolicy_home_node sys_set_mempolicy_home_node
+451 i386 cachestat sys_cachestat
@@ -372,6 +372,7 @@
448 common process_mrelease sys_process_mrelease
449 common futex_waitv sys_futex_waitv
450 common set_mempolicy_home_node sys_set_mempolicy_home_node
+451 common cachestat sys_cachestat
#
# Due to a historical design error, certain syscalls are numbered differently
@@ -421,3 +421,4 @@
448 common process_mrelease sys_process_mrelease
449 common futex_waitv sys_futex_waitv
450 common set_mempolicy_home_node sys_set_mempolicy_home_node
+451 common cachestat sys_cachestat
@@ -75,6 +75,7 @@ struct fs_context;
struct fs_parameter_spec;
struct fileattr;
struct iomap_ops;
+struct cachestat;
extern void __init inode_init(void);
extern void __init inode_init_early(void);
@@ -830,6 +831,8 @@ void filemap_invalidate_lock_two(struct address_space *mapping1,
struct address_space *mapping2);
void filemap_invalidate_unlock_two(struct address_space *mapping1,
struct address_space *mapping2);
+void filemap_cachestat(struct address_space *mapping, pgoff_t first_index,
+ pgoff_t last_index, struct cachestat *cs);
/*
@@ -72,6 +72,7 @@ struct open_how;
struct mount_attr;
struct landlock_ruleset_attr;
enum landlock_rule_type;
+struct cachestat;
#include <linux/types.h>
#include <linux/aio_abi.h>
@@ -1056,6 +1057,9 @@ asmlinkage long sys_memfd_secret(unsigned int flags);
asmlinkage long sys_set_mempolicy_home_node(unsigned long start, unsigned long len,
unsigned long home_node,
unsigned long flags);
+asmlinkage long sys_cachestat(unsigned int fd, off_t off, size_t len,
+ unsigned int cstat_version, struct cachestat __user *cstat,
+ unsigned int flags);
/*
* Architecture-specific system calls
@@ -886,8 +886,11 @@ __SYSCALL(__NR_futex_waitv, sys_futex_waitv)
#define __NR_set_mempolicy_home_node 450
__SYSCALL(__NR_set_mempolicy_home_node, sys_set_mempolicy_home_node)
+#define __NR_cachestat 451
+__SYSCALL(__NR_cachestat, sys_cachestat)
+
#undef __NR_syscalls
-#define __NR_syscalls 451
+#define __NR_syscalls 452
/*
* 32 bit systems traditionally used different
@@ -4,6 +4,7 @@
#include <asm/mman.h>
#include <asm-generic/hugetlb_encode.h>
+#include <linux/types.h>
#define MREMAP_MAYMOVE 1
#define MREMAP_FIXED 2
@@ -41,4 +42,12 @@
#define MAP_HUGE_2GB HUGETLB_FLAG_ENCODE_2GB
#define MAP_HUGE_16GB HUGETLB_FLAG_ENCODE_16GB
+struct cachestat {
+ __u64 nr_cache;
+ __u64 nr_dirty;
+ __u64 nr_writeback;
+ __u64 nr_evicted;
+ __u64 nr_recently_evicted;
+};
+
#endif /* _UAPI_LINUX_MMAN_H */
@@ -1798,6 +1798,16 @@ config RSEQ
If unsure, say Y.
+config CACHESTAT_SYSCALL
+ bool "Enable cachestat() system call" if EXPERT
+ default y
+ help
+ Enable the cachestat system call, which queries the page cache
+ statistics of a file (number of cached pages, dirty pages,
+ pages marked for writeback, (recently) evicted pages).
+
+ If unsure say Y here.
+
config DEBUG_RSEQ
default n
bool "Enabled debugging of rseq() system call" if EXPERT
@@ -299,6 +299,7 @@ COND_SYSCALL(set_mempolicy);
COND_SYSCALL(migrate_pages);
COND_SYSCALL(move_pages);
COND_SYSCALL(set_mempolicy_home_node);
+COND_SYSCALL(cachestat);
COND_SYSCALL(perf_event_open);
COND_SYSCALL(accept4);
@@ -22,6 +22,7 @@
#include <linux/mm.h>
#include <linux/swap.h>
#include <linux/swapops.h>
+#include <linux/syscalls.h>
#include <linux/mman.h>
#include <linux/pagemap.h>
#include <linux/file.h>
@@ -55,6 +56,13 @@
#include <linux/buffer_head.h> /* for try_to_free_buffers */
#include <asm/mman.h>
+#include <uapi/linux/mman.h>
+
+#include "swap.h"
+
+#ifdef CONFIG_CACHESTAT_SYSCALL
+#define LATEST_CACHESTAT_VERSION 1
+#endif
/*
* Shared mappings implemented 30.11.1994. It's not fully working yet,
@@ -3949,3 +3957,149 @@ bool filemap_release_folio(struct folio *folio, gfp_t gfp)
return try_to_free_buffers(folio);
}
EXPORT_SYMBOL(filemap_release_folio);
+
+/**
+ * filemap_cachestat() - compute the page cache statistics of a mapping
+ * @mapping: The mapping to compute the statistics for.
+ * @first_index: The starting page cache index.
+ * @last_index: The final page index (inclusive).
+ * @cs: the cachestat struct to write the result to.
+ *
+ * This will query the page cache statistics of a mapping in the
+ * page range of [first_index, last_index] (inclusive). The statistics
+ * queried include: number of dirty pages, number of pages marked for
+ * writeback, and the number of (recently) evicted pages.
+ */
+void filemap_cachestat(struct address_space *mapping, pgoff_t first_index,
+ pgoff_t last_index, struct cachestat *cs)
+{
+ XA_STATE(xas, &mapping->i_pages, first_index);
+ struct folio *folio;
+
+ rcu_read_lock();
+ xas_for_each(&xas, folio, last_index) {
+ unsigned long nr_pages;
+ pgoff_t folio_first_index, folio_last_index;
+
+ if (xas_retry(&xas, folio))
+ continue;
+
+ nr_pages = folio_nr_pages(folio);
+ folio_first_index = folio_pgoff(folio);
+ folio_last_index = folio_first_index + nr_pages - 1;
+
+ /* Folios might straddle the range boundaries, only count covered subpages */
+ if (folio_first_index < first_index)
+ nr_pages -= first_index - folio_first_index;
+
+ if (folio_last_index > last_index)
+ nr_pages -= folio_last_index - last_index;
+
+ if (xa_is_value(folio)) {
+ /* page is evicted */
+ void *shadow = (void *)folio;
+ bool workingset; /* not used */
+
+ cs->nr_evicted += nr_pages;
+
+#ifdef CONFIG_SWAP /* implies CONFIG_MMU */
+ if (shmem_mapping(mapping)) {
+ /* shmem file - in swap cache */
+ swp_entry_t swp = radix_to_swp_entry(folio);
+
+ shadow = get_shadow_from_swap_cache(swp);
+ }
+#endif
+ if (workingset_test_recent(shadow, true, &workingset))
+ cs->nr_recently_evicted += nr_pages;
+
+ goto resched;
+ }
+
+ /* page is in cache */
+ cs->nr_cache += nr_pages;
+
+ if (folio_test_dirty(folio))
+ cs->nr_dirty += nr_pages;
+
+ if (folio_test_writeback(folio))
+ cs->nr_writeback += nr_pages;
+
+resched:
+ if (need_resched()) {
+ xas_pause(&xas);
+ cond_resched_rcu();
+ }
+ }
+ rcu_read_unlock();
+}
+EXPORT_SYMBOL(filemap_cachestat);
+
+#ifdef CONFIG_CACHESTAT_SYSCALL
+/*
+ * The cachestat(5) system call.
+ *
+ * cachestat() returns the page cache statistics of a file in the
+ * bytes range specified by `off` and `len`: number of cached pages,
+ * number of dirty pages, number of pages marked for writeback,
+ * number of evicted pages, and number of recently evicted pages.
+ *
+ * An evicted page is a page that is previously in the page cache
+ * but has been evicted since. A page is recently evicted if its last
+ * eviction was recent enough that its reentry to the cache would
+ * indicate that it is actively being used by the system, and that
+ * there is memory pressure on the system.
+ *
+ * `off` and `len` must be non-negative integers. If `len` > 0,
+ * the queried range is [`off`, `off` + `len`]. If `len` == 0,
+ * we will query in the range from `off` to the end of the file.
+ *
+ * `cstat_version` is an unsigned integer indicating the specific version
+ * of the cachestat struct. It must be at least 1, and does not exceed the
+ * latest version number (which is currently 1). For now, user should
+ * just pass 1.
+ *
+ * The `flags` argument is unused for now, but is included for future
+ * extensibility. User should pass 0 (i.e no flag specified).
+ *
+ * Because the status of a page can change after cachestat() checks it
+ * but before it returns to the application, the returned values may
+ * contain stale information.
+ *
+ * return values:
+ * zero - success
+ * -EFAULT - cstat points to an illegal address
+ * -EINVAL - invalid arguments
+ * -EBADF - invalid file descriptor
+ */
+SYSCALL_DEFINE6(cachestat, unsigned int, fd, off_t, off, size_t, len,
+ unsigned int, cstat_version, struct cachestat __user *, cstat,
+ unsigned int, flags)
+{
+ struct fd f = fdget(fd);
+ struct address_space *mapping;
+ struct cachestat cs;
+ pgoff_t first_index = off >> PAGE_SHIFT;
+ pgoff_t last_index =
+ len == 0 ? ULONG_MAX : (off + len - 1) >> PAGE_SHIFT;
+
+ if (!f.file)
+ return -EBADF;
+
+ if (off < 0 || flags != 0 || cstat_version < 1 ||
+ cstat_version > LATEST_CACHESTAT_VERSION) {
+ fdput(f);
+ return -EINVAL;
+ }
+
+ memset(&cs, 0, sizeof(struct cachestat));
+ mapping = f.file->f_mapping;
+ filemap_cachestat(mapping, first_index, last_index, &cs);
+ fdput(f);
+
+ if (copy_to_user(cstat, &cs, sizeof(struct cachestat)))
+ return -EFAULT;
+
+ return 0;
+}
+#endif /* CONFIG_CACHESTAT_SYSCALL */