[PATCH v3] fadvise: introduce POSIX_FADV_DONTNEED_FS
From: Andrea Righi
Date: Fri Apr 29 2011 - 12:19:53 EST
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
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