Re: swsusp performance problems in 2.6.15-rc3-mm1

From: Andrew Morton
Date: Sat Dec 10 2005 - 18:33:10 EST

"Rafael J. Wysocki" <rjw@xxxxxxx> wrote:
>
> Would that be ok if I made drop_pagecache() nonstatic and called it directly
> from swsusp?

Sure, I'll updates the patch for that.

It changed a bit.. You'll need to run sys_sync() then drop_pagecache()
then drop_slab().


From: Andrew Morton <akpm@xxxxxxxx>

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.

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.


Signed-off-by: Andrew Morton <akpm@xxxxxxxx>
---

Documentation/filesystems/proc.txt | 17 +++++++++
Documentation/sysctl/vm.txt | 3 +
fs/Makefile | 2 -
fs/drop_caches.c | 68 +++++++++++++++++++++++++++++++++++++
include/linux/mm.h | 7 +++
include/linux/sysctl.h | 1
kernel/sysctl.c | 10 +++++
mm/truncate.c | 1
mm/vmscan.c | 3 -
9 files changed, 107 insertions(+), 5 deletions(-)

diff -puN /dev/null fs/drop_caches.c
--- /dev/null 2003-09-15 06:40:47.000000000 -0700
+++ devel-akpm/fs/drop_caches.c 2005-12-10 15:31:19.000000000 -0800
@@ -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 -puN fs/Makefile~drop-pagecache fs/Makefile
--- devel/fs/Makefile~drop-pagecache 2005-12-10 15:30:17.000000000 -0800
+++ devel-akpm/fs/Makefile 2005-12-10 15:30:17.000000000 -0800
@@ -10,7 +10,7 @@ obj-y := open.o read_write.o file_table.
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 -puN include/linux/mm.h~drop-pagecache include/linux/mm.h
--- devel/include/linux/mm.h~drop-pagecache 2005-12-10 15:30:17.000000000 -0800
+++ devel-akpm/include/linux/mm.h 2005-12-10 15:31:35.000000000 -0800
@@ -1010,5 +1010,12 @@ int in_gate_area_no_task(unsigned long a
/* /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 -puN include/linux/sysctl.h~drop-pagecache include/linux/sysctl.h
--- devel/include/linux/sysctl.h~drop-pagecache 2005-12-10 15:30:17.000000000 -0800
+++ devel-akpm/include/linux/sysctl.h 2005-12-10 15:30:17.000000000 -0800
@@ -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 */
};


diff -puN kernel/sysctl.c~drop-pagecache kernel/sysctl.c
--- devel/kernel/sysctl.c~drop-pagecache 2005-12-10 15:30:17.000000000 -0800
+++ devel-akpm/kernel/sysctl.c 2005-12-10 15:30:17.000000000 -0800
@@ -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,
diff -puN mm/truncate.c~drop-pagecache mm/truncate.c
--- devel/mm/truncate.c~drop-pagecache 2005-12-10 15:30:17.000000000 -0800
+++ devel-akpm/mm/truncate.c 2005-12-10 15:30:17.000000000 -0800
@@ -249,7 +249,6 @@ unlock:
break;
}
pagevec_release(&pvec);
- cond_resched();
}
return ret;
}
diff -puN mm/vmscan.c~drop-pagecache mm/vmscan.c
--- devel/mm/vmscan.c~drop-pagecache 2005-12-10 15:30:17.000000000 -0800
+++ devel-akpm/mm/vmscan.c 2005-12-10 15:30:17.000000000 -0800
@@ -183,8 +183,7 @@ 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;
diff -puN Documentation/sysctl/vm.txt~drop-pagecache Documentation/sysctl/vm.txt
--- devel/Documentation/sysctl/vm.txt~drop-pagecache 2005-12-10 15:30:17.000000000 -0800
+++ devel-akpm/Documentation/sysctl/vm.txt 2005-12-10 15:30:17.000000000 -0800
@@ -26,12 +26,13 @@ Currently, these files are in /proc/sys/
- 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 -puN Documentation/filesystems/proc.txt~drop-pagecache Documentation/filesystems/proc.txt
--- devel/Documentation/filesystems/proc.txt~drop-pagecache 2005-12-10 15:30:17.000000000 -0800
+++ devel-akpm/Documentation/filesystems/proc.txt 2005-12-10 15:30:17.000000000 -0800
@@ -1302,6 +1302,23 @@ VM has token based thrashing control mec
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 caches:
+ echo 1 > /proc/sys/vm/drop_caches
+To free dentries and inodes:
+ echo 2 > /proc/sys/vm/drop_caches
+To free caches, 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
----------------------------------------------

_

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