Introduce a new fadvise flag to drop page cache pages of a single filesystem. At the moment it is possible to drop page cache pages via /proc/sys/vm/drop_pagecache or via posix_fadvise(POSIX_FADV_DONTNEED). The first method drops the whole page cache while the second can be used to drop page cache pages of a single file descriptor. However, there's not a simple way to drop all the pages of a filesystem (we could scan all the file descriptors and use posix_fadvise(POSIX_FADV_DONTNEED), but this solution obviously doesn't scale well). NOTE #1: to avoid potential DoS in the system the rate of calls to fadvise(POSIX_FADV_DONTNEED_FS) from non-privileged users are limited according to these settings: - /proc/sys/vm/drop_pagecache_ratelimit: the minimum length of time allowed beetween two different bursts of fadvise(POSIX_FADV_DONTNEED_FS) - /proc/sys/vm/drop_pagecache_ratelimit_burst: the number of calls to fadvise(POSIX_FADV_DONTNEED_FS) that can be issued before enforcing the rate limiting When the rate limit is exceeded the function returns -EPERM. NOTE #2: for a regular file, drops the pages of the superblock it references; for a block device, drops the pages of the superblock corresponding to the device (if mounted). A practical example: # ls -lh /mnt/sda/zero /mnt/sdb/zero -rw-r--r-- 1 root root 16M 2011-04-20 10:20 /mnt/sda/zero -rw-r--r-- 1 root root 16M 2011-04-20 10:20 /mnt/sdb/zero $ grep ^Cached /proc/meminfo Cached: 5660 kB $ md5sum /mnt/sda/zero /mnt/sdb/zero 2c7ab85a893283e98c931e9511add182 /mnt/sda/zero 2c7ab85a893283e98c931e9511add182 /mnt/sdb/zero $ grep ^Cached /proc/meminfo Cached: 38544 kB $ ./drop-pagecache /mnt/sda/ $ grep ^Cached /proc/meminfo Cached: 22440 kB $ ./drop-pagecache /mnt/sdb/ $ grep ^Cached /proc/meminfo Cached: 5056 kB A previous RFC about this topic can be found here: http://marc.info/?l=linux-kernel&m=130385374902114&w=2 ChangeLog (v2 -> v3): * limit the rate of POSIX_FADV_DONTNEED_FS if executed by a non-privileged user * if fadvise() is called on a block devices (i.e. /dev/sda) drop the pages of the superblock corresponding to this device (if mounted) Signed-off-by: Andrea Righi <andrea@xxxxxxxxxxxxxxx> --- Documentation/sysctl/vm.txt | 22 ++++++++++++++++++++++ fs/drop_caches.c | 2 +- include/linux/fadvise.h | 1 + include/linux/mm.h | 4 ++++ kernel/sysctl.c | 14 ++++++++++++++ mm/fadvise.c | 37 +++++++++++++++++++++++++++++++++++++ 6 files changed, 79 insertions(+), 1 deletions(-) diff --git a/Documentation/sysctl/vm.txt b/Documentation/sysctl/vm.txt index 30289fa..39aa7e3 100644 --- a/Documentation/sysctl/vm.txt +++ b/Documentation/sysctl/vm.txt @@ -27,6 +27,8 @@ Currently, these files are in /proc/sys/vm: - dirty_ratio - dirty_writeback_centisecs - drop_caches +- drop_pagecache_ratelimit +- drop_pagecache_ratelimit_burst - extfrag_threshold - hugepages_treat_as_movable - hugetlb_shm_group @@ -154,6 +156,26 @@ user should run `sync' first. ============================================================== +drop_pagecache_ratelimit + +To avoid potential DoS in the system the rate of calls to +fadvise(POSIX_FADV_DONTNEED_FS) from non-privileged users are limited. + +This value defines the minimum length of time allowed beetween two different +bursts of fadvise(POSIX_FADV_DONTNEED_FS). + +============================================================== + +drop_pagecache_ratelimit_burst + +To avoid potential DoS in the system the rate of calls to +fadvise(POSIX_FADV_DONTNEED_FS) from non-privileged users are limited. + +This value defines the number of calls to fadvise(POSIX_FADV_DONTNEED_FS) that +can be issued before enforcing the rate limiting. + +============================================================== + extfrag_threshold This parameter affects whether the kernel will compact memory or direct diff --git a/fs/drop_caches.c b/fs/drop_caches.c index 98b77c8..59d6caa 100644 --- a/fs/drop_caches.c +++ b/fs/drop_caches.c @@ -13,7 +13,7 @@ /* A global variable is a bit ugly, but it keeps the code simple */ int sysctl_drop_caches; -static void drop_pagecache_sb(struct super_block *sb, void *unused) +void drop_pagecache_sb(struct super_block *sb, void *unused) { struct inode *inode, *toput_inode = NULL; diff --git a/include/linux/fadvise.h b/include/linux/fadvise.h index e8e7471..ab39117 100644 --- a/include/linux/fadvise.h +++ b/include/linux/fadvise.h @@ -17,5 +17,6 @@ #define POSIX_FADV_DONTNEED 4 /* Don't need these pages. */ #define POSIX_FADV_NOREUSE 5 /* Data will be accessed once. */ #endif +#define POSIX_FADV_DONTNEED_FS 8 /* Don't need these filesystem pages. */ #endif /* FADVISE_H_INCLUDED */ diff --git a/include/linux/mm.h b/include/linux/mm.h index 2348db2..2d57612 100644 --- a/include/linux/mm.h +++ b/include/linux/mm.h @@ -14,6 +14,7 @@ #include <linux/mm_types.h> #include <linux/range.h> #include <linux/pfn.h> +#include <linux/ratelimit.h> #include <linux/bit_spinlock.h> struct mempolicy; @@ -21,6 +22,7 @@ struct anon_vma; struct file_ra_state; struct user_struct; struct writeback_control; +struct super_block; #ifndef CONFIG_DISCONTIGMEM /* Don't use mapnrs, do it properly */ extern unsigned long max_mapnr; @@ -33,6 +35,7 @@ extern int page_cluster; #ifdef CONFIG_SYSCTL extern int sysctl_legacy_va_layout; +extern struct ratelimit_state drop_pagecache_ratelimit_state; #else #define sysctl_legacy_va_layout 0 #endif @@ -1603,6 +1606,7 @@ int in_gate_area_no_mm(unsigned long addr); #define in_gate_area(mm, addr) ({(void)mm; in_gate_area_no_mm(addr);}) #endif /* __HAVE_ARCH_GATE_AREA */ +void drop_pagecache_sb(struct super_block *sb, void *unused); int drop_caches_sysctl_handler(struct ctl_table *, int, void __user *, size_t *, loff_t *); unsigned long shrink_slab(unsigned long scanned, gfp_t gfp_mask, diff --git a/kernel/sysctl.c b/kernel/sysctl.c index c0bb324..4d404ae 100644 --- a/kernel/sysctl.c +++ b/kernel/sysctl.c @@ -1145,6 +1145,20 @@ static struct ctl_table vm_table[] = { .extra1 = &one, .extra2 = &three, }, + { + .procname = "drop_pagecache_ratelimit", + .data = &drop_pagecache_ratelimit_state.interval, + .maxlen = sizeof(int), + .mode = 0644, + .proc_handler = proc_dointvec_jiffies, + }, + { + .procname = "drop_pagecache_ratelimit_burst", + .data = &drop_pagecache_ratelimit_state.burst, + .maxlen = sizeof(int), + .mode = 0644, + .proc_handler = proc_dointvec, + }, #ifdef CONFIG_COMPACTION { .procname = "compact_memory", diff --git a/mm/fadvise.c b/mm/fadvise.c index 8d723c9..8adf620 100644 --- a/mm/fadvise.c +++ b/mm/fadvise.c @@ -16,10 +16,39 @@ #include <linux/pagevec.h> #include <linux/fadvise.h> #include <linux/writeback.h> +#include <linux/ratelimit.h> #include <linux/syscalls.h> #include <asm/unistd.h> +/* Limit the rate of the page cache drop */ +DEFINE_RATELIMIT_STATE(drop_pagecache_ratelimit_state, + DEFAULT_RATELIMIT_INTERVAL, DEFAULT_RATELIMIT_BURST); + +static inline struct super_block *file_to_sb(struct file *file) +{ + struct block_device *bdev = I_BDEV(file->f_mapping->host); + + return bdev ? get_super(bdev) : NULL; +} + +/* + * For a regular file, drop the pages of the superblock it references. For a + * block device, drop the pages of the superblock corresponding to this device + * (if mounted). + */ +static void fadvise_drop_pagecache(struct file *file) +{ + struct super_block *sb; + + sb = file_to_sb(file); + if (sb) { + drop_pagecache_sb(sb, NULL); + drop_super(sb); + } else + drop_pagecache_sb(file->f_mapping->host->i_sb, NULL); +} + /* * POSIX_FADV_WILLNEED could set PG_Referenced, and POSIX_FADV_NOREUSE could * deactivate the pages and clear PG_Referenced. @@ -57,6 +86,7 @@ SYSCALL_DEFINE(fadvise64_64)(int fd, loff_t offset, loff_t len, int advice) case POSIX_FADV_WILLNEED: case POSIX_FADV_NOREUSE: case POSIX_FADV_DONTNEED: + case POSIX_FADV_DONTNEED_FS: /* no bad return value, but ignore advice */ break; default: @@ -127,6 +157,13 @@ SYSCALL_DEFINE(fadvise64_64)(int fd, loff_t offset, loff_t len, int advice) invalidate_mapping_pages(mapping, start_index, end_index); break; + case POSIX_FADV_DONTNEED_FS: + if (capable(CAP_SYS_ADMIN) || + __ratelimit(&drop_pagecache_ratelimit_state)) + fadvise_drop_pagecache(file); + else + ret = -EPERM; + break; default: ret = -EINVAL; } -- 1.7.1 -- To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
