[v2,3/4] cachestat: implement cachestat syscall

Message ID	20221205175140.1543229-4-nphamcs@gmail.com (mailing list archive)
State	New
Headers	show Return-Path: <owner-linux-mm@kvack.org> From: Nhat Pham <nphamcs@gmail.com> To: akpm@linux-foundation.org Cc: hannes@cmpxchg.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org, bfoster@redhat.com, willy@infradead.org, kernel-team@meta.com Subject: [PATCH v2 3/4] cachestat: implement cachestat syscall Date: Mon, 5 Dec 2022 09:51:39 -0800 Message-Id: <20221205175140.1543229-4-nphamcs@gmail.com> In-Reply-To: <20221205175140.1543229-1-nphamcs@gmail.com> References: <20221205175140.1543229-1-nphamcs@gmail.com> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Sender: owner-linux-mm@kvack.org Precedence: bulk
Series	cachestat: a new syscall for page cache state of files \| expand [v2,0/4] cachestat: a new syscall for page cache state of files [v2,1/4] workingset: fix confusion around eviction vs refault container [v2,2/4] workingset: refactor LRU refault to expose refault recency check [v2,3/4] cachestat: implement cachestat syscall [v2,4/4] selftests: Add selftests for cachestat

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@gmail.com> +M: Johannes Weiner <hannes@cmpxchg.org> +L: linux-mm@kvack.org +S: Maintained +F: mm/cachestat.c + CADENCE MIPI-CSI2 BRIDGES M: Maxime Ripard <mripard@kernel.org> L: linux-media@vger.kernel.org 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/include/linux/syscalls.h b/include/linux/syscalls.h index a34b0f9a9972..55cea19b8bf6 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); /* * 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..ee2889e0654e 100644 --- a/include/uapi/linux/mman.h +++ b/include/uapi/linux/mman.h @@ -41,4 +41,12 @@ #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/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..e71b15743ce6 100644 --- a/mm/Makefile +++ b/mm/Makefile @@ -54,7 +54,7 @@ obj-y := filemap.o mempool.o oom_kill.o fadvise.o \ mm_init.o percpu.o slab_common.o \ compaction.o \ interval_tree.o list_lru.o workingset.o \ - debug.o gup.o mmap_lock.o $(mmu-y) + debug.o gup.o mmap_lock.o cachestat.o $(mmu-y) # Give 'page_alloc' its own module-parameter namespace page-alloc-y := page_alloc.o diff --git a/mm/cachestat.c b/mm/cachestat.c new file mode 100644 index 000000000000..59067f26eba3 --- /dev/null +++ b/mm/cachestat.c @@ -0,0 +1,115 @@ +// 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(4) 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. + * + * 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_DEFINE5(cachestat, unsigned int, fd, off_t, off, size_t, len, + size_t, cstat_size, struct cachestat __user *, cstat) +{ + struct fd f; + struct cachestat cs; + + memset(&cs, 0, sizeof(struct cachestat)); + + if (off < 0 || len < 0 || + cstat_size > sizeof(struct cachestat) || + cstat_size < 0) + return -EINVAL; + + if (!access_ok(cstat, sizeof(struct cachestat))) + return -EFAULT; + + f = fdget(fd); + if (f.file) { + struct address_space *mapping = f.file->f_mapping; + pgoff_t first_index = off >> PAGE_SHIFT; + pgoff_t last_index = + len == 0 ? ULONG_MAX : (off + len - 1) >> PAGE_SHIFT; + XA_STATE(xas, &mapping->i_pages, first_index); + struct folio *folio; + + rcu_read_lock(); + xas_for_each(&xas, folio, last_index) { + if (xas_retry(&xas, folio) || !folio) + continue; + + if (xa_is_value(folio)) { + /* page is evicted */ + void *shadow = (void *)folio; + bool workingset; /* not used */ + + cs.nr_evicted += 1; + +#if defined(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 += 1; + + continue; + } + + /* page is in cache */ + cs.nr_cache += 1; + + if (folio_test_dirty(folio)) + cs.nr_dirty += 1; + + if (folio_test_writeback(folio)) + cs.nr_writeback += 1; + } + rcu_read_unlock(); + fdput(f); + + if (copy_to_user(cstat, &cs, cstat_size)) + return -EFAULT; + + return 0; + } + + return -EBADF; +}

[v2,3/4] cachestat: implement cachestat syscall

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