[PATCH] fadvise: introduce POSIX_FADV_DONTNEED_FS
From: Andrea Righi <hidden>
Date: 2011-04-27 14:29:05
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). This functionality requires root privilege to avoid potential DoS in the system (i.e., a hard loop of posix_fadvise(POSIX_FADV_DONTNEED_FS) on the root filesystem). 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 $ sudo ./drop-pagecache /mnt/sda/ $ grep ^Cached /proc/meminfo Cached: 22440 kB $ sudo ./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 Signed-off-by: Andrea Righi <redacted> --- fs/drop_caches.c | 2 +- include/linux/fadvise.h | 2 ++ include/linux/mm.h | 2 ++ mm/fadvise.c | 7 +++++++ 4 files changed, 12 insertions(+), 1 deletions(-)
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..dc9ce98 100644
--- a/include/linux/fadvise.h
+++ b/include/linux/fadvise.h@@ -13,9 +13,11 @@ #if defined(__s390x__) #define POSIX_FADV_DONTNEED 6 /* Don't need these pages. */ #define POSIX_FADV_NOREUSE 7 /* Data will be accessed once. */ +#define POSIX_FADV_DONTNEED_FS 8 /* Don't need these filesystem pages. */ #else #define POSIX_FADV_DONTNEED 4 /* Don't need these pages. */ #define POSIX_FADV_NOREUSE 5 /* Data will be accessed once. */ +#define POSIX_FADV_DONTNEED_FS 6 /* Don't need these filesystem pages. */ #endif #endif /* FADVISE_H_INCLUDED */
diff --git a/include/linux/mm.h b/include/linux/mm.h
index 692dbae..004cdbc 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h@@ -21,6 +21,7 @@ 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;
@@ -1602,6 +1603,7 @@ 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/mm/fadvise.c b/mm/fadvise.c
index 8d723c9..4e31fe1 100644
--- a/mm/fadvise.c
+++ b/mm/fadvise.c@@ -57,6 +57,7 @@ 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 +128,12 @@ 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 (!current_euid()) + drop_pagecache_sb(file->f_dentry->d_sb, NULL); + else + ret = -EPERM; + break; default: ret = -EINVAL; }
--
1.7.1