projects/linux·commit 9d0243bc

[PATCH] drop-pagecache

9d0243bc · Andrew Morton <[email protected]> · 2006-01-08 01:00:39 -08:00

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 <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>
Commit
9d0243bca345d5ce25d3f4b74b7facb3a6df1232
Parents
bec6b0c8

Changes

9 files changed · +107 −5

FileStatusAddDelContent
Documentation/filesystems/proc.txtmodified+17−0View file
Documentation/sysctl/vm.txtmodified+2−1View file
fs/Makefilemodified+1−1View file
fs/drop_caches.cadded+68−0View file
include/linux/mm.hmodified+7−0View file
include/linux/sysctl.hmodified+1−0View file
kernel/sysctl.cmodified+10−0View file
mm/truncate.cmodified+0−1View file
mm/vmscan.cmodified+1−2View file

Documentation/filesystems/proc.txt

View file
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 @@ VM has token based thrashing control mechanism and uses the token to prevent
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
----------------------------------------------

Documentation/sysctl/vm.txt

View file
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 @@ Currently, these files are in /proc/sys/vm:
- 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

fs/Makefile

View file
diff --git a/fs/Makefile b/fs/Makefile
index 7367611..35e9aec 100644
--- a/fs/Makefile
+++ b/fs/Makefile
@@ -10,7 +10,7 @@ obj-y := open.o read_write.o file_table.o buffer.o bio.o super.o \
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

fs/drop_caches.c

View file
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;
+}

include/linux/mm.h

View file
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 @@ int in_gate_area_no_task(unsigned long addr);
/* /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 */

include/linux/sysctl.h

View file
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 @@ enum
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 */
};

kernel/sysctl.c

View file
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 min_free_kbytes;
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 @@ static ctl_table vm_table[] = {
.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,

mm/truncate.c

View file
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 @@ unlock:
break;
}
pagevec_release(&pvec);
- cond_resched();
}
return ret;
}

mm/vmscan.c

View file
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 @@ EXPORT_SYMBOL(remove_shrinker);
*
* 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;