diff mbox series

[v12,2/3] cachestat: implement cachestat syscall

Message ID 20230421231421.2401346-3-nphamcs@gmail.com (mailing list archive)
State New
Headers show
Series cachestat: a new syscall for page cache state of files | expand

Commit Message

Nhat Pham April 21, 2023, 11:14 p.m. UTC 
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

kernel test robot April 22, 2023, 2:35 a.m. UTC | #1 
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]
kernel test robot April 22, 2023, 9:56 a.m. UTC | #2 
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);
kernel test robot April 28, 2023, 8:40 a.m. UTC | #3 
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"
diff mbox series

Patch

diff --git a/arch/x86/entry/syscalls/syscall_32.tbl b/arch/x86/entry/syscalls/syscall_32.tbl
index 320480a8db4f..01d1cc009250 100644
--- a/arch/x86/entry/syscalls/syscall_32.tbl
+++ b/arch/x86/entry/syscalls/syscall_32.tbl
@@ -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
diff --git a/arch/x86/entry/syscalls/syscall_64.tbl b/arch/x86/entry/syscalls/syscall_64.tbl
index c84d12608cd2..227538b0ce80 100644
--- a/arch/x86/entry/syscalls/syscall_64.tbl
+++ b/arch/x86/entry/syscalls/syscall_64.tbl
@@ -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
diff --git a/include/linux/compat.h b/include/linux/compat.h
index 44b1736c95b5..ed7227603c7e 100644
--- a/include/linux/compat.h
+++ b/include/linux/compat.h
@@ -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,
diff --git a/include/linux/syscalls.h b/include/linux/syscalls.h
index 33a0ee3bcb2e..73c174fda520 100644
--- a/include/linux/syscalls.h
+++ b/include/linux/syscalls.h
@@ -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
diff --git a/include/uapi/asm-generic/unistd.h b/include/uapi/asm-generic/unistd.h
index 45fa180cc56a..dc5fcfee7f09 100644
--- a/include/uapi/asm-generic/unistd.h
+++ b/include/uapi/asm-generic/unistd.h
@@ -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
diff --git a/include/uapi/linux/mman.h b/include/uapi/linux/mman.h
index f55bc680b5b0..fe03ed0b7587 100644
--- a/include/uapi/linux/mman.h
+++ b/include/uapi/linux/mman.h
@@ -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 */
diff --git a/init/Kconfig b/init/Kconfig
index 1fb5f313d18f..10de68cbd6b6 100644
--- a/init/Kconfig
+++ b/init/Kconfig
@@ -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
diff --git a/kernel/sys_ni.c b/kernel/sys_ni.c
index 860b2dcf3ac4..04bfb1e4d377 100644
--- a/kernel/sys_ni.c
+++ b/kernel/sys_ni.c
@@ -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);
diff --git a/mm/filemap.c b/mm/filemap.c
index a34abfe8c654..9819722569a5 100644
--- a/mm/filemap.c
+++ b/mm/filemap.c
@@ -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 */