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[2a03:2880:ff:1::face:b00c]) by smtp.gmail.com with ESMTPSA id ja13-20020a170902efcd00b0017f7c4e260fsm10233512plb.150.2022.11.15.10.29.06 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 15 Nov 2022 10:29:06 -0800 (PST) From: Nhat Pham To: linux-mm@kvack.org, linux-kernel@vger.kernel.org Cc: hannes@cmpxchg.org Subject: [PATCH 3/4] cachestat: implement cachestat syscall Date: Tue, 15 Nov 2022 10:29:00 -0800 Message-Id: <20221115182901.2755368-4-nphamcs@gmail.com> X-Mailer: git-send-email 2.30.2 In-Reply-To: <20221115182901.2755368-1-nphamcs@gmail.com> References: <20221115182901.2755368-1-nphamcs@gmail.com> MIME-Version: 1.0 X-Spam-Status: No, score=-2.1 required=5.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,DKIM_VALID_EF,FREEMAIL_FROM, RCVD_IN_DNSWL_NONE,SPF_HELO_NONE,SPF_PASS autolearn=ham autolearn_force=no version=3.4.6 X-Spam-Checker-Version: SpamAssassin 3.4.6 (2021-04-09) on lindbergh.monkeyblade.net Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org X-getmail-retrieved-from-mailbox: =?utf-8?q?INBOX?= X-GMAIL-THRID: =?utf-8?q?1749588237025130120?= X-GMAIL-MSGID: =?utf-8?q?1749588237025130120?= 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 struct cachestat { unsigned long nr_cache; unsigned long nr_dirty; unsigned long nr_writeback; unsigned long nr_evicted; unsigned long nr_recently_evicted; }; int cachestat(unsigned int fd, off_t off, size_t len, struct cachestat *cstat); 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` argument must be a non-negative integers, If `off` + `len` >= `off`, the queried range is [`off`, `off` + `len`]. Otherwise, we will query in the range from `off` to the end of the file. 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 `off` is negative. EBADF invalid file descriptor. Signed-off-by: Nhat Pham --- MAINTAINERS | 7 ++ arch/x86/entry/syscalls/syscall_32.tbl | 1 + arch/x86/entry/syscalls/syscall_64.tbl | 1 + include/linux/syscalls.h | 2 + include/uapi/asm-generic/unistd.h | 5 +- include/uapi/linux/mman.h | 8 ++ kernel/sys_ni.c | 1 + mm/Makefile | 2 +- mm/cachestat.c | 109 +++++++++++++++++++++++++ 9 files changed, 134 insertions(+), 2 deletions(-) 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 +M: Johannes Weiner +L: linux-mm@kvack.org +S: Maintained +F: mm/cachestat.c + CADENCE MIPI-CSI2 BRIDGES M: Maxime Ripard 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..59e4d56225ae 100644 --- a/include/linux/syscalls.h +++ b/include/linux/syscalls.h @@ -1056,6 +1056,8 @@ 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, + struct cachestat __user *ret_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..8690c82acd02 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 { + unsigned long nr_cache; + unsigned long nr_dirty; + unsigned long nr_writeback; + unsigned long nr_evicted; + unsigned long 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..193151cb0767 --- /dev/null +++ b/mm/cachestat.c @@ -0,0 +1,109 @@ +// SPDX-License-Identifier: GPL-2.0-or-later + +/* + * The cachestat() system call. + */ +#include +#include +#include +#include +#include +#include +#include + +#include "swap.h" + +/* + * The cachestat(3) 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. + * + * If `off` + `len` >= `off`, the queried range is [`off`, `off` + `len`]. + * Otherwise, we will query in the range from `off` to the end of the file. + * + * 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_DEFINE4(cachestat, unsigned int, fd, off_t, off, size_t, len, + struct cachestat __user *, cstat) +{ + struct fd f; + struct cachestat cs; + + memset(&cs, 0, sizeof(struct cachestat)); + + if (off < 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; + XA_STATE(xas, &mapping->i_pages, first_index); + struct folio *folio; + pgoff_t last_index = (off + len - 1) >> PAGE_SHIFT; + + if (last_index < first_index) + last_index = ULONG_MAX; + + 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; + bool workingset; /* not used */ + + cs.nr_evicted += 1; + + 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); + } else { + /* in page cache */ + shadow = (void *) folio; + } + + 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, sizeof(struct cachestat))) + return -EFAULT; + + return 0; + } + + return -EBADF; +}