[v12,2/3] 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.
A couple of use cases where this information could come in handy:
* Deciding whether to perform an index scan or direct table queries
based on the in-memory cache state of the index.
* Visibility into the writeback algorithm, for performance issues
diagnostic.
* Userspace writeback advise - balancing between integrity and IO
utilization.
* Computing memory usage of large files/directory trees, analogous to
the du tool for disk usage.
More information about these use cases could be found in the following
thread:
https://lore.kernel.org/lkml/20230315170934.GA97793@cmpxchg.org/
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. Currently, the syscall is only wired in for x86
architecture.
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, size_t len, loff_t off,
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.
The `flags` argument is unused for now, but is included for future
extensibility. User should pass 0 (i.e no flag specified).
Currently, hugetlbfs is not supported.
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 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 offset or flags.
EBADF invalid file descriptor.
EOPNOTSUPP file descriptor is of a hugetlbfs file
Signed-off-by: Nhat Pham <nphamcs@gmail.com>
---
arch/x86/entry/syscalls/syscall_32.tbl | 1 +
arch/x86/entry/syscalls/syscall_64.tbl | 1 +
include/linux/compat.h | 4 +
include/linux/syscalls.h | 3 +
include/uapi/asm-generic/unistd.h | 5 +-
include/uapi/linux/mman.h | 9 ++
init/Kconfig | 10 ++
kernel/sys_ni.c | 1 +
mm/filemap.c | 179 +++++++++++++++++++++++++
9 files changed, 212 insertions(+), 1 deletion(-)
Comments
Hi Nhat,
kernel test robot noticed the following build warnings:
[auto build test WARNING on akpm-mm/mm-everything]
[cannot apply to shuah-kselftest/next shuah-kselftest/fixes linus/master tip/x86/asm v6.3-rc7 next-20230421]
[If your patch is applied to the wrong git tree, kindly drop us a note.
And when submitting patch, we suggest to use '--base' as documented in
https://git-scm.com/docs/git-format-patch#_base_tree_information]
url: https://github.com/intel-lab-lkp/linux/commits/Nhat-Pham/workingset-refactor-LRU-refault-to-expose-refault-recency-check/20230422-071625
base: https://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm.git mm-everything
patch link: https://lore.kernel.org/r/20230421231421.2401346-3-nphamcs%40gmail.com
patch subject: [PATCH v12 2/3] cachestat: implement cachestat syscall
config: m68k-allyesconfig (https://download.01.org/0day-ci/archive/20230422/202304221049.51AIFM7O-lkp@intel.com/config)
compiler: m68k-linux-gcc (GCC) 12.1.0
reproduce (this is a W=1 build):
wget https://raw.githubusercontent.com/intel/lkp-tests/master/sbin/make.cross -O ~/bin/make.cross
chmod +x ~/bin/make.cross
# https://github.com/intel-lab-lkp/linux/commit/9691e4430fbb59890619289b45ee0ce9ec3e97ee
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/20230422-071625
git checkout 9691e4430fbb59890619289b45ee0ce9ec3e97ee
# save the config file
mkdir build_dir && cp config build_dir/.config
COMPILER_INSTALL_PATH=$HOME/0day COMPILER=gcc-12.1.0 make.cross W=1 O=build_dir ARCH=m68k olddefconfig
COMPILER_INSTALL_PATH=$HOME/0day COMPILER=gcc-12.1.0 make.cross W=1 O=build_dir ARCH=m68k prepare
If you fix the issue, kindly add following tag where applicable
| Reported-by: kernel test robot <lkp@intel.com>
| Link: https://lore.kernel.org/oe-kbuild-all/202304221049.51AIFM7O-lkp@intel.com/
All warnings (new ones prefixed by >>):
>> <stdin>:1567:2: warning: #warning syscall cachestat not implemented [-Wcpp]
--
>> <stdin>:1567:2: warning: #warning syscall cachestat not implemented [-Wcpp]
--
scripts/genksyms/parse.y: warning: 9 shift/reduce conflicts [-Wconflicts-sr]
scripts/genksyms/parse.y: warning: 5 reduce/reduce conflicts [-Wconflicts-rr]
scripts/genksyms/parse.y: note: rerun with option '-Wcounterexamples' to generate conflict counterexamples
>> <stdin>:1567:2: warning: #warning syscall cachestat not implemented [-Wcpp]
Hi Nhat,
kernel test robot noticed the following build errors:
[auto build test ERROR on akpm-mm/mm-everything]
[cannot apply to shuah-kselftest/next shuah-kselftest/fixes linus/master tip/x86/asm v6.3-rc7 next-20230421]
[If your patch is applied to the wrong git tree, kindly drop us a note.
And when submitting patch, we suggest to use '--base' as documented in
https://git-scm.com/docs/git-format-patch#_base_tree_information]
url: https://github.com/intel-lab-lkp/linux/commits/Nhat-Pham/workingset-refactor-LRU-refault-to-expose-refault-recency-check/20230422-071625
base: https://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm.git mm-everything
patch link: https://lore.kernel.org/r/20230421231421.2401346-3-nphamcs%40gmail.com
patch subject: [PATCH v12 2/3] cachestat: implement cachestat syscall
config: x86_64-randconfig-a016 (https://download.01.org/0day-ci/archive/20230422/202304221702.Ye705xoC-lkp@intel.com/config)
compiler: clang version 14.0.6 (https://github.com/llvm/llvm-project f28c006a5895fc0e329fe15fead81e37457cb1d1)
reproduce (this is a W=1 build):
wget https://raw.githubusercontent.com/intel/lkp-tests/master/sbin/make.cross -O ~/bin/make.cross
chmod +x ~/bin/make.cross
# https://github.com/intel-lab-lkp/linux/commit/9691e4430fbb59890619289b45ee0ce9ec3e97ee
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/20230422-071625
git checkout 9691e4430fbb59890619289b45ee0ce9ec3e97ee
# save the config file
mkdir build_dir && cp config build_dir/.config
COMPILER_INSTALL_PATH=$HOME/0day COMPILER=clang make.cross W=1 O=build_dir ARCH=x86_64 olddefconfig
COMPILER_INSTALL_PATH=$HOME/0day COMPILER=clang make.cross W=1 O=build_dir ARCH=x86_64 SHELL=/bin/bash
If you fix the issue, kindly add following tag where applicable
| Reported-by: kernel test robot <lkp@intel.com>
| Link: https://lore.kernel.org/oe-kbuild-all/202304221702.Ye705xoC-lkp@intel.com/
All error/warnings (new ones prefixed by >>):
>> mm/filemap.c:4293:35: error: expected identifier
COMPAT_SYSCALL_DEFINE6(cachestat, unsigned int, fd, size_t, len,
^
>> mm/filemap.c:4293:1: error: type specifier missing, defaults to 'int' [-Werror,-Wimplicit-int]
COMPAT_SYSCALL_DEFINE6(cachestat, unsigned int, fd, size_t, len,
^
>> mm/filemap.c:4297:33: error: implicit declaration of function 'compat_arg_u64_glue' is invalid in C99 [-Werror,-Wimplicit-function-declaration]
return ksys_cachestat(fd, len, compat_arg_u64_glue(off), cstat, flags);
^
>> mm/filemap.c:4297:24: error: use of undeclared identifier 'fd'
return ksys_cachestat(fd, len, compat_arg_u64_glue(off), cstat, flags);
^
>> mm/filemap.c:4297:28: error: use of undeclared identifier 'len'
return ksys_cachestat(fd, len, compat_arg_u64_glue(off), cstat, flags);
^
>> mm/filemap.c:4297:53: error: use of undeclared identifier 'off'
return ksys_cachestat(fd, len, compat_arg_u64_glue(off), cstat, flags);
^
>> mm/filemap.c:4297:59: error: use of undeclared identifier 'cstat'
return ksys_cachestat(fd, len, compat_arg_u64_glue(off), cstat, flags);
^
>> mm/filemap.c:4297:66: error: use of undeclared identifier 'flags'
return ksys_cachestat(fd, len, compat_arg_u64_glue(off), cstat, flags);
^
>> mm/filemap.c:4293:1: warning: no previous prototype for function 'COMPAT_SYSCALL_DEFINE6' [-Wmissing-prototypes]
COMPAT_SYSCALL_DEFINE6(cachestat, unsigned int, fd, size_t, len,
^
mm/filemap.c:4293:23: note: declare 'static' if the function is not intended to be used outside of this translation unit
COMPAT_SYSCALL_DEFINE6(cachestat, unsigned int, fd, size_t, len,
^
static
>> mm/filemap.c:4293:23: error: this old-style function definition is not preceded by a prototype [-Werror,-Wstrict-prototypes]
COMPAT_SYSCALL_DEFINE6(cachestat, unsigned int, fd, size_t, len,
^
1 warning and 9 errors generated.
vim +4293 mm/filemap.c
4291
4292 #ifdef CONFIG_COMPAT
> 4293 COMPAT_SYSCALL_DEFINE6(cachestat, unsigned int, fd, size_t, len,
4294 compat_arg_u64_dual(off), struct cachestat __user *, cstat,
4295 unsigned int, flags)
4296 {
> 4297 return ksys_cachestat(fd, len, compat_arg_u64_glue(off), cstat, flags);
Hi Nhat,
kernel test robot noticed the following build warnings:
[auto build test WARNING on akpm-mm/mm-everything]
[cannot apply to shuah-kselftest/next shuah-kselftest/fixes linus/master tip/x86/asm v6.3-rc7 next-20230421]
[If your patch is applied to the wrong git tree, kindly drop us a note.
And when submitting patch, we suggest to use '--base' as documented in
https://git-scm.com/docs/git-format-patch#_base_tree_information]
url: https://github.com/intel-lab-lkp/linux/commits/Nhat-Pham/workingset-refactor-LRU-refault-to-expose-refault-recency-check/20230422-071625
base: https://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm.git mm-everything
patch link: https://lore.kernel.org/r/20230421231421.2401346-3-nphamcs%40gmail.com
patch subject: [PATCH v12 2/3] cachestat: implement cachestat syscall
compiler: gcc-11 (Debian 11.3.0-8) 11.3.0
If you fix the issue, kindly add following tag where applicable
| Reported-by: kernel test robot <yujie.liu@intel.com>
| Link: https://lore.kernel.org/r/202304230337.Qd5oUtzU-lkp@intel.com/
includecheck warnings: (new ones prefixed by >>)
>> mm/filemap.c: linux/mman.h is included more than once.
ffa65753c4314 (Alistair Popple 2022-01-21 22:10:46 -0800 24) #include <linux/swapops.h>
9691e4430fbb5 (Nhat Pham 2023-04-21 16:14:20 -0700 25) #include <linux/syscalls.h>
^1da177e4c3f4 (Linus Torvalds 2005-04-16 15:20:36 -0700 @26) #include <linux/mman.h>
^1da177e4c3f4 (Linus Torvalds 2005-04-16 15:20:36 -0700 27) #include <linux/pagemap.h>
^1da177e4c3f4 (Linus Torvalds 2005-04-16 15:20:36 -0700 28) #include <linux/file.h>
^1da177e4c3f4 (Linus Torvalds 2005-04-16 15:20:36 -0700 29) #include <linux/uio.h>
cfcbfb1382dba (Josef Bacik 2019-05-13 17:21:04 -0700 30) #include <linux/error-injection.h>
^1da177e4c3f4 (Linus Torvalds 2005-04-16 15:20:36 -0700 31) #include <linux/hash.h>
^1da177e4c3f4 (Linus Torvalds 2005-04-16 15:20:36 -0700 32) #include <linux/writeback.h>
53253383fde9e (Linus Torvalds 2007-10-18 14:47:32 -0700 33) #include <linux/backing-dev.h>
^1da177e4c3f4 (Linus Torvalds 2005-04-16 15:20:36 -0700 34) #include <linux/pagevec.h>
^1da177e4c3f4 (Linus Torvalds 2005-04-16 15:20:36 -0700 35) #include <linux/security.h>
44110fe385af2 (Paul Jackson 2006-03-24 03:16:04 -0800 36) #include <linux/cpuset.h>
00501b531c472 (Johannes Weiner 2014-08-08 14:19:20 -0700 37) #include <linux/hugetlb.h>
8a9f3ccd24741 (Balbir Singh 2008-02-07 00:13:53 -0800 38) #include <linux/memcontrol.h>
c7df8ad2910e9 (Mel Gorman 2017-11-15 17:37:41 -0800 39) #include <linux/shmem_fs.h>
f1820361f83d5 (Kirill A. Shutemov 2014-04-07 15:37:19 -0700 40) #include <linux/rmap.h>
b1d29ba82cf2b (Johannes Weiner 2018-10-26 15:06:08 -0700 41) #include <linux/delayacct.h>
eb414681d5a07 (Johannes Weiner 2018-10-26 15:06:27 -0700 42) #include <linux/psi.h>
d0e6a5821cdf0 (Ben Dooks 2019-10-18 20:20:20 -0700 43) #include <linux/ramfs.h>
b9306a796cad8 (Yang Shi 2020-08-06 23:19:55 -0700 44) #include <linux/page_idle.h>
ffa65753c4314 (Alistair Popple 2022-01-21 22:10:46 -0800 45) #include <linux/migrate.h>
07073eb01c5f6 (David Howells 2023-02-14 15:01:42 +0000 46) #include <linux/pipe_fs_i.h>
07073eb01c5f6 (David Howells 2023-02-14 15:01:42 +0000 47) #include <linux/splice.h>
f9ce0be71d1fb (Kirill A. Shutemov 2020-12-19 15:19:23 +0300 48) #include <asm/pgalloc.h>
de591a82f41b6 (Will Deacon 2021-02-10 11:15:11 +0000 49) #include <asm/tlbflush.h>
0f8053a509ceb (Nicholas Piggin 2006-03-22 00:08:33 -0800 50) #include "internal.h"
0f8053a509ceb (Nicholas Piggin 2006-03-22 00:08:33 -0800 51)
fe0bfaaff8442 (Robert Jarzmik 2013-04-29 15:06:10 -0700 52) #define CREATE_TRACE_POINTS
fe0bfaaff8442 (Robert Jarzmik 2013-04-29 15:06:10 -0700 53) #include <trace/events/filemap.h>
fe0bfaaff8442 (Robert Jarzmik 2013-04-29 15:06:10 -0700 54)
^1da177e4c3f4 (Linus Torvalds 2005-04-16 15:20:36 -0700 55) /*
^1da177e4c3f4 (Linus Torvalds 2005-04-16 15:20:36 -0700 56) * FIXME: remove all knowledge of the buffer layer from the core VM
^1da177e4c3f4 (Linus Torvalds 2005-04-16 15:20:36 -0700 57) */
148f948ba877f (Jan Kara 2009-08-17 19:52:36 +0200 58) #include <linux/buffer_head.h> /* for try_to_free_buffers */
^1da177e4c3f4 (Linus Torvalds 2005-04-16 15:20:36 -0700 59)
^1da177e4c3f4 (Linus Torvalds 2005-04-16 15:20:36 -0700 60) #include <asm/mman.h>
9691e4430fbb5 (Nhat Pham 2023-04-21 16:14:20 -0700 @61) #include <linux/mman.h>
9691e4430fbb5 (Nhat Pham 2023-04-21 16:14:20 -0700 62)
9691e4430fbb5 (Nhat Pham 2023-04-21 16:14:20 -0700 63) #include "swap.h"
@@ -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 compat_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
@@ -424,6 +424,7 @@ struct compat_sysctl_args;
struct compat_kexec_segment;
struct compat_mq_attr;
struct compat_msgbuf;
+struct cachestat;
void copy_siginfo_to_external32(struct compat_siginfo *to,
const struct kernel_siginfo *from);
@@ -815,6 +816,9 @@ asmlinkage long compat_sys_recvmsg(int fd, struct compat_msghdr __user *msg,
unsigned int flags);
/* mm/filemap.c: No generic prototype for readahead */
+asmlinkage long compat_sys_cachestat(unsigned int fd, size_t len,
+ compat_arg_u64(off), struct cachestat __user *cstat,
+ unsigned int flags);
/* security/keys/keyctl.c */
asmlinkage long compat_sys_keyctl(u32 option,
@@ -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>
@@ -1058,6 +1059,8 @@ 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, size_t len, loff_t offset,
+ 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
+__SC_COMP(__NR_cachestat, sys_cachestat, compat_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 */
@@ -1837,6 +1837,16 @@ 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>
@@ -57,6 +58,9 @@
#include <linux/buffer_head.h> /* for try_to_free_buffers */
#include <asm/mman.h>
+#include <linux/mman.h>
+
+#include "swap.h"
/*
* Shared mappings implemented 30.11.1994. It's not fully working yet,
@@ -4119,3 +4123,178 @@ 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.
+ */
+static 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;
+
+ if (xa_is_value(folio)) {
+ /* page is evicted */
+ void *shadow = (void *)folio;
+ bool workingset; /* not used */
+ int order = xa_get_order(xas.xa, xas.xa_index);
+
+ nr_pages = 1 << order;
+ /* rounds down to the nearest multiple of 2^order */
+ folio_first_index = xas.xa_index >> order << order;
+ folio_last_index = folio_first_index + nr_pages - 1;
+
+ /* Folios might straddle the range boundaries, only count covered pages */
+ 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;
+
+ 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;
+ }
+
+ 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 pages */
+ 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;
+
+ /* 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();
+}
+
+#ifdef CONFIG_CACHESTAT_SYSCALL
+static long ksys_cachestat(unsigned int fd, size_t len, loff_t off,
+ 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;
+
+ /* hugetlbfs is not supported */
+ if (is_file_hugepages(f.file)) {
+ fdput(f);
+ return -EOPNOTSUPP;
+ }
+
+ if (off < 0 || flags != 0) {
+ 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;
+}
+
+/*
+ * 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.
+ *
+ * The `flags` argument is unused for now, but is included for future
+ * extensibility. User should pass 0 (i.e no flag specified).
+ *
+ * Currently, hugetlbfs is not supported.
+ *
+ * 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
+ * -EOPNOTSUPP - file descriptor is of a hugetlbfs file
+ */
+SYSCALL_DEFINE5(cachestat, unsigned int, fd, size_t, len, loff_t, off,
+ struct cachestat __user *, cstat, unsigned int, flags)
+{
+ return ksys_cachestat(fd, len, off, cstat, flags);
+}
+
+#ifdef CONFIG_COMPAT
+COMPAT_SYSCALL_DEFINE6(cachestat, unsigned int, fd, size_t, len,
+ compat_arg_u64_dual(off), struct cachestat __user *, cstat,
+ unsigned int, flags)
+{
+ return ksys_cachestat(fd, len, compat_arg_u64_glue(off), cstat, flags);
+}
+#endif
+#endif /* CONFIG_CACHESTAT_SYSCALL */