[PATCH] drop-pagecache
Add /proc/sys/vm/drop_caches. When written to, this will cause the kernel to
discard as much pagecache and/or reclaimable slab objects as it can. THis
operation requires root permissions.
It won't drop dirty data, so the user should run `sync' first.
Caveats:
a) Holds inode_lock for exorbitant amounts of time.
b) Needs to be taught about NUMA nodes: propagate these all the way through
so the discarding can be controlled on a per-node basis.
This is a debugging feature: useful for getting consistent results between
filesystem benchmarks. We could possibly put it under a config option, but
it's less than 300 bytes.
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
diff --git a/Documentation/filesystems/proc.txt b/Documentation/filesystems/proc.txt
index d477356..a4dcf42 100644
--- a/Documentation/filesystems/proc.txt
+++ b/Documentation/filesystems/proc.txt
@@ -1302,6 +1302,23 @@
unnecessary page faults in thrashing situation. The unit of the value is
second. The value would be useful to tune thrashing behavior.
+drop_caches
+-----------
+
+Writing to this will cause the kernel to drop clean caches, dentries and
+inodes from memory, causing that memory to become free.
+
+To free pagecache:
+ echo 1 > /proc/sys/vm/drop_caches
+To free dentries and inodes:
+ echo 2 > /proc/sys/vm/drop_caches
+To free pagecache, dentries and inodes:
+ echo 3 > /proc/sys/vm/drop_caches
+
+As this is a non-destructive operation and dirty objects are not freeable, the
+user should run `sync' first.
+
+
2.5 /proc/sys/dev - Device specific parameters
----------------------------------------------
diff --git a/Documentation/sysctl/vm.txt b/Documentation/sysctl/vm.txt
index 2f1aae3..89ba1a4 100644
--- a/Documentation/sysctl/vm.txt
+++ b/Documentation/sysctl/vm.txt
@@ -26,12 +26,13 @@
- min_free_kbytes
- laptop_mode
- block_dump
+- drop-caches
==============================================================
dirty_ratio, dirty_background_ratio, dirty_expire_centisecs,
dirty_writeback_centisecs, vfs_cache_pressure, laptop_mode,
-block_dump, swap_token_timeout:
+block_dump, swap_token_timeout, drop-caches:
See Documentation/filesystems/proc.txt
diff --git a/fs/Makefile b/fs/Makefile
index 7367611..35e9aec 100644
--- a/fs/Makefile
+++ b/fs/Makefile
@@ -10,7 +10,7 @@
ioctl.o readdir.o select.o fifo.o locks.o dcache.o inode.o \
attr.o bad_inode.o file.o filesystems.o namespace.o aio.o \
seq_file.o xattr.o libfs.o fs-writeback.o mpage.o direct-io.o \
- ioprio.o pnode.o
+ ioprio.o pnode.o drop_caches.o
obj-$(CONFIG_INOTIFY) += inotify.o
obj-$(CONFIG_EPOLL) += eventpoll.o
diff --git a/fs/drop_caches.c b/fs/drop_caches.c
new file mode 100644
index 0000000..4e47623
--- /dev/null
+++ b/fs/drop_caches.c
@@ -0,0 +1,68 @@
+/*
+ * Implement the manual drop-all-pagecache function
+ */
+
+#include <linux/kernel.h>
+#include <linux/mm.h>
+#include <linux/fs.h>
+#include <linux/writeback.h>
+#include <linux/sysctl.h>
+#include <linux/gfp.h>
+
+/* 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)
+{
+ struct inode *inode;
+
+ spin_lock(&inode_lock);
+ list_for_each_entry(inode, &sb->s_inodes, i_sb_list) {
+ if (inode->i_state & (I_FREEING|I_WILL_FREE))
+ continue;
+ invalidate_inode_pages(inode->i_mapping);
+ }
+ spin_unlock(&inode_lock);
+}
+
+void drop_pagecache(void)
+{
+ struct super_block *sb;
+
+ spin_lock(&sb_lock);
+restart:
+ list_for_each_entry(sb, &super_blocks, s_list) {
+ sb->s_count++;
+ spin_unlock(&sb_lock);
+ down_read(&sb->s_umount);
+ if (sb->s_root)
+ drop_pagecache_sb(sb);
+ up_read(&sb->s_umount);
+ spin_lock(&sb_lock);
+ if (__put_super_and_need_restart(sb))
+ goto restart;
+ }
+ spin_unlock(&sb_lock);
+}
+
+void drop_slab(void)
+{
+ int nr_objects;
+
+ do {
+ nr_objects = shrink_slab(1000, GFP_KERNEL, 1000);
+ } while (nr_objects > 10);
+}
+
+int drop_caches_sysctl_handler(ctl_table *table, int write,
+ struct file *file, void __user *buffer, size_t *length, loff_t *ppos)
+{
+ proc_dointvec_minmax(table, write, file, buffer, length, ppos);
+ if (write) {
+ if (sysctl_drop_caches & 1)
+ drop_pagecache();
+ if (sysctl_drop_caches & 2)
+ drop_slab();
+ }
+ return 0;
+}
diff --git a/include/linux/mm.h b/include/linux/mm.h
index bc01fff..83c651f 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -1036,5 +1036,12 @@
/* /proc/<pid>/oom_adj set to -17 protects from the oom-killer */
#define OOM_DISABLE -17
+int drop_caches_sysctl_handler(struct ctl_table *, int, struct file *,
+ void __user *, size_t *, loff_t *);
+int shrink_slab(unsigned long scanned, gfp_t gfp_mask,
+ unsigned long lru_pages);
+void drop_pagecache(void);
+void drop_slab(void);
+
#endif /* __KERNEL__ */
#endif /* _LINUX_MM_H */
diff --git a/include/linux/sysctl.h b/include/linux/sysctl.h
index a9b80fc..4cd267f 100644
--- a/include/linux/sysctl.h
+++ b/include/linux/sysctl.h
@@ -180,6 +180,7 @@
VM_VFS_CACHE_PRESSURE=26, /* dcache/icache reclaim pressure */
VM_LEGACY_VA_LAYOUT=27, /* legacy/compatibility virtual address space layout */
VM_SWAP_TOKEN_TIMEOUT=28, /* default time for token time out */
+ VM_DROP_PAGECACHE=29, /* int: nuke lots of pagecache */
};
diff --git a/kernel/sysctl.c b/kernel/sysctl.c
index a85047b..8dcf6fd 100644
--- a/kernel/sysctl.c
+++ b/kernel/sysctl.c
@@ -68,6 +68,7 @@
extern int printk_ratelimit_jiffies;
extern int printk_ratelimit_burst;
extern int pid_max_min, pid_max_max;
+extern int sysctl_drop_caches;
#if defined(CONFIG_X86_LOCAL_APIC) && defined(CONFIG_X86)
int unknown_nmi_panic;
@@ -775,6 +776,15 @@
.strategy = &sysctl_intvec,
},
{
+ .ctl_name = VM_DROP_PAGECACHE,
+ .procname = "drop_caches",
+ .data = &sysctl_drop_caches,
+ .maxlen = sizeof(int),
+ .mode = 0644,
+ .proc_handler = drop_caches_sysctl_handler,
+ .strategy = &sysctl_intvec,
+ },
+ {
.ctl_name = VM_MIN_FREE_KBYTES,
.procname = "min_free_kbytes",
.data = &min_free_kbytes,
diff --git a/mm/truncate.c b/mm/truncate.c
index 7dee327..b1a463d 100644
--- a/mm/truncate.c
+++ b/mm/truncate.c
@@ -249,7 +249,6 @@
break;
}
pagevec_release(&pvec);
- cond_resched();
}
return ret;
}
diff --git a/mm/vmscan.c b/mm/vmscan.c
index be8235f..428c580 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -180,8 +180,7 @@
*
* Returns the number of slab objects which we shrunk.
*/
-static int shrink_slab(unsigned long scanned, gfp_t gfp_mask,
- unsigned long lru_pages)
+int shrink_slab(unsigned long scanned, gfp_t gfp_mask, unsigned long lru_pages)
{
struct shrinker *shrinker;
int ret = 0;