| Message ID | 20230126175356.1582123-3-nphamcs@gmail.com (mailing list archive) |
|---|---|
| State | New |
| Headers | show |
| Series | cachestat: a new syscall for page cache state of files | expand |
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,
diff --git a/arch/alpha/kernel/syscalls/syscall.tbl b/arch/alpha/kernel/syscalls/syscall.tbl index 8ebacf37a8cf..1f13995d00d7 100644 --- a/arch/alpha/kernel/syscalls/syscall.tbl +++ b/arch/alpha/kernel/syscalls/syscall.tbl @@ -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 diff --git a/arch/arm/tools/syscall.tbl b/arch/arm/tools/syscall.tbl index ac964612d8b0..8ebed8a13874 100644 --- a/arch/arm/tools/syscall.tbl +++ b/arch/arm/tools/syscall.tbl @@ -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 diff --git a/arch/ia64/kernel/syscalls/syscall.tbl b/arch/ia64/kernel/syscalls/syscall.tbl index 72c929d9902b..f8c74ffeeefb 100644 --- a/arch/ia64/kernel/syscalls/syscall.tbl +++ b/arch/ia64/kernel/syscalls/syscall.tbl @@ -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 diff --git a/arch/m68k/kernel/syscalls/syscall.tbl b/arch/m68k/kernel/syscalls/syscall.tbl index b1f3940bc298..4f504783371f 100644 --- a/arch/m68k/kernel/syscalls/syscall.tbl +++ b/arch/m68k/kernel/syscalls/syscall.tbl @@ -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 diff --git a/arch/microblaze/kernel/syscalls/syscall.tbl b/arch/microblaze/kernel/syscalls/syscall.tbl index 820145e47350..858d22bf275c 100644 --- a/arch/microblaze/kernel/syscalls/syscall.tbl +++ b/arch/microblaze/kernel/syscalls/syscall.tbl @@ -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 diff --git a/arch/mips/kernel/syscalls/syscall_n32.tbl b/arch/mips/kernel/syscalls/syscall_n32.tbl index 253ff994ed2e..1976317d4e8b 100644 --- a/arch/mips/kernel/syscalls/syscall_n32.tbl +++ b/arch/mips/kernel/syscalls/syscall_n32.tbl @@ -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 diff --git a/arch/mips/kernel/syscalls/syscall_n64.tbl b/arch/mips/kernel/syscalls/syscall_n64.tbl index 3f1886ad9d80..cfda2511badf 100644 --- a/arch/mips/kernel/syscalls/syscall_n64.tbl +++ b/arch/mips/kernel/syscalls/syscall_n64.tbl @@ -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 diff --git a/arch/mips/kernel/syscalls/syscall_o32.tbl b/arch/mips/kernel/syscalls/syscall_o32.tbl index 8f243e35a7b2..7692234c3768 100644 --- a/arch/mips/kernel/syscalls/syscall_o32.tbl +++ b/arch/mips/kernel/syscalls/syscall_o32.tbl @@ -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 diff --git a/arch/parisc/kernel/syscalls/syscall.tbl b/arch/parisc/kernel/syscalls/syscall.tbl index 8a99c998da9b..7c84a72306d1 100644 --- a/arch/parisc/kernel/syscalls/syscall.tbl +++ b/arch/parisc/kernel/syscalls/syscall.tbl @@ -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 diff --git a/arch/powerpc/kernel/syscalls/syscall.tbl b/arch/powerpc/kernel/syscalls/syscall.tbl index 2bca64f96164..937460f0a8ec 100644 --- a/arch/powerpc/kernel/syscalls/syscall.tbl +++ b/arch/powerpc/kernel/syscalls/syscall.tbl @@ -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 diff --git a/arch/s390/kernel/syscalls/syscall.tbl b/arch/s390/kernel/syscalls/syscall.tbl index 799147658dee..7df0329d46cb 100644 --- a/arch/s390/kernel/syscalls/syscall.tbl +++ b/arch/s390/kernel/syscalls/syscall.tbl @@ -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 diff --git a/arch/sh/kernel/syscalls/syscall.tbl b/arch/sh/kernel/syscalls/syscall.tbl index 2de85c977f54..97377e8c5025 100644 --- a/arch/sh/kernel/syscalls/syscall.tbl +++ b/arch/sh/kernel/syscalls/syscall.tbl @@ -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 diff --git a/arch/sparc/kernel/syscalls/syscall.tbl b/arch/sparc/kernel/syscalls/syscall.tbl index 4398cc6fb68d..faa835f3c54a 100644 --- a/arch/sparc/kernel/syscalls/syscall.tbl +++ b/arch/sparc/kernel/syscalls/syscall.tbl @@ -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 diff --git a/arch/x86/entry/syscalls/syscall_32.tbl b/arch/x86/entry/syscalls/syscall_32.tbl index 320480a8db4f..bc0a3c941b35 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 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/arch/xtensa/kernel/syscalls/syscall.tbl b/arch/xtensa/kernel/syscalls/syscall.tbl index 52c94ab5c205..2b69c3c035b6 100644 --- a/arch/xtensa/kernel/syscalls/syscall.tbl +++ b/arch/xtensa/kernel/syscalls/syscall.tbl @@ -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 diff --git a/include/linux/fs.h b/include/linux/fs.h index e654435f1651..83300f1491e7 100644 --- a/include/linux/fs.h +++ b/include/linux/fs.h @@ -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); /* diff --git a/include/linux/syscalls.h b/include/linux/syscalls.h index a34b0f9a9972..d3fe6ba8eb38 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> @@ -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 diff --git a/include/uapi/asm-generic/unistd.h b/include/uapi/asm-generic/unistd.h index 45fa180cc56a..cd639fae9086 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 +__SYSCALL(__NR_cachestat, 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 694f7c160c9c..da96ac29af1d 100644 --- a/init/Kconfig +++ b/init/Kconfig @@ -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 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 08341616ae7a..0305eaf5b3f5 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> @@ -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 */
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(-)