On Thu, Dec 8, 2022 at 12:28 PM Nhat Pham <nphamcs@xxxxxxxxx> wrote: > > Implement 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 status 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, > size_t cstat_size, 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 (recently) > evicted pages, in the bytes range given by `off` and `len`. > > 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_size` allows users to obtain partial results. The syscall > will copy the first `csstat_size` bytes to the specified userspace > memory. `cstat_size` must be a non-negative value that is no larger > than the current size of the cachestat struct. > > 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_size` or `flags` > > EBADF invalid file descriptor. > > Signed-off-by: Nhat Pham <nphamcs@xxxxxxxxx> > --- > MAINTAINERS | 7 ++ > 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/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/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/Makefile | 1 + > mm/cachestat.c | 117 ++++++++++++++++++++ > 21 files changed, 165 insertions(+), 1 deletion(-) > create mode 100644 mm/cachestat.c > > diff --git a/MAINTAINERS b/MAINTAINERS > index a198da986146..baa081a1fe52 100644 > --- a/MAINTAINERS > +++ b/MAINTAINERS > @@ -4552,6 +4552,13 @@ S: Supported > F: Documentation/filesystems/caching/cachefiles.rst > F: fs/cachefiles/ > > +CACHESTAT: PAGE CACHE STATS FOR A FILE > +M: Nhat Pham <nphamcs@xxxxxxxxx> > +M: Johannes Weiner <hannes@xxxxxxxxxxx> > +L: linux-mm@xxxxxxxxx > +S: Maintained > +F: mm/cachestat.c > + > CADENCE MIPI-CSI2 BRIDGES > M: Maxime Ripard <mripard@xxxxxxxxxx> > L: linux-media@xxxxxxxxxxxxxxx > 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/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..8eed4cdc7965 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/syscalls.h b/include/linux/syscalls.h > index a34b0f9a9972..50f8c6999d99 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 +1057,8 @@ 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, off_t off, size_t len, > + size_t cstat_size, 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..ecc4f781dd6c 100644 > --- a/init/Kconfig > +++ b/init/Kconfig > @@ -1798,6 +1798,16 @@ config RSEQ > > If unsure, say Y. > > +config CACHESTAT > + 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/Makefile b/mm/Makefile > index 8e105e5b3e29..61c9c3f81cef 100644 > --- a/mm/Makefile > +++ b/mm/Makefile > @@ -138,3 +138,4 @@ obj-$(CONFIG_IO_MAPPING) += io-mapping.o > obj-$(CONFIG_HAVE_BOOTMEM_INFO_NODE) += bootmem_info.o > obj-$(CONFIG_GENERIC_IOREMAP) += ioremap.o > obj-$(CONFIG_SHRINKER_DEBUG) += shrinker_debug.o > +obj-$(CONFIG_CACHESTAT) += cachestat.o > diff --git a/mm/cachestat.c b/mm/cachestat.c > new file mode 100644 > index 000000000000..931f5e37326b > --- /dev/null > +++ b/mm/cachestat.c > @@ -0,0 +1,117 @@ > +// SPDX-License-Identifier: GPL-2.0-or-later > + > +/* > + * The cachestat() system call. > + */ > +#include <linux/file.h> > +#include <linux/fs.h> > +#include <linux/syscalls.h> > +#include <linux/shmem_fs.h> > +#include <linux/swap.h> > +#include <linux/swapops.h> > +#include <uapi/linux/mman.h> > + > +#include "swap.h" > + > +/* > + * The cachestat(5) system call. > + * > + * cachestat() returns the page cache status of a file in the > + * bytes specified by `off` and `len`: number of cached pages, > + * number of dirty pages, number of pages marked for writeback, > + * number of (recently) evicted pages. > + * > + * `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_size` allows users to obtain partial results. The syscall > + * will copy the first `csstat_size` bytes to the specified userspace > + * memory. It also makes the cachestat struct extensible - new fields > + * can be added in the future without breaking existing usage. > + * `cstat_size` must be a non-negative value that is no larger than > + * the current size of the cachestat struct. > + * > + * 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, > + size_t, cstat_size, struct cachestat __user *, cstat, > + unsigned int, flags) > +{ > + struct fd f; > + struct cachestat cs; > + > + memset(&cs, 0, sizeof(struct cachestat)); > + > + if (off < 0 || cstat_size > sizeof(struct cachestat) || flags != 0) > + return -EINVAL; > + > + if (!access_ok(cstat, sizeof(struct cachestat))) > + return -EFAULT; Oops, this part should really be: if (!access_ok(cstat, cstat_size)) I'll send a new version of patch 3/4 to fix this...