Re: [PATCH 0/4] linux-2.6-block: deactivating pagecache for benchmarks

Andrew Morton
2005-12-02T01:25:38Z

Dirk Henning Gerdes <mail@dirk-gerdes.de> wrote:
>
> For doing benchmarks on the I/O-Schedulers, I thought it would be very
> useful to disable the pagecache.

That's an FAQ. Something like this?

From: Andrew Morton <akpm@osdl.org>

Add /proc/sys/vm/drop-pagecache. When written to, this will cause the kernel
to discard as much pagecache and 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.

c) The pagecache shrinking and slab shrinking should probably have separate
controls.

Signed-off-by: Andrew Morton <akpm@osdl.org>
---

fs/Makefile | 2 -
fs/drop-pagecache.c | 62 +++++++++++++++++++++++++++++++++++++++++++++++++
include/linux/mm.h | 5 +++
include/linux/sysctl.h | 1
kernel/sysctl.c | 9 +++++++
mm/truncate.c | 1
mm/vmscan.c | 3 --
7 files changed, 79 insertions(+), 4 deletions(-)

diff -puN /dev/null fs/drop-pagecache.c
--- /dev/null 2003-09-15 06:40:47.000000000 -0700
+++ devel-akpm/fs/drop-pagecache.c 2005-12-01 17:20:55.000000000 -0800
@@ -0,0 +1,62 @@
+/*
+ * 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>
+
+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);
+}
+
+static 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);
+ printk("shrunk pagecache\n");
+}
+
+static void drop_slab(void)
+{
+ int nr_objects;
+
+ do {
+ nr_objects = shrink_slab(1000, GFP_KERNEL, 1000);
+ printk("shrunk %d cache objects\n", nr_objects);
+ } while (nr_objects > 10);
+}
+
+int drop_pagecache_sysctl_handler(ctl_table *table, int write,
+ struct file *file, void __user *buffer, size_t *length, loff_t *ppos)
+{
+ drop_pagecache();
+ drop_slab();
+ return 0;
+}
diff -puN fs/Makefile~drop-pagecache fs/Makefile
--- devel/fs/Makefile~drop-pagecache 2005-12-01 16:41:22.000000000 -0800
+++ devel-akpm/fs/Makefile 2005-12-01 16:41:22.000000000 -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-pagecache.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 2005-12-01 16:41:22.000000000 -0800
+++ devel-akpm/include/linux/mm.h 2005-12-01 17:01:57.000000000 -0800
@@ -1078,5 +1078,10 @@ 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_pagecache_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);
+
#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 2005-12-01 16:41:22.000000000 -0800
+++ devel-akpm/include/linux/sysctl.h 2005-12-01 16:41:22.000000000 -0800
@@ -182,6 +182,7 @@ enum
VM_LEGACY_VA_LAYOUT=27, /* legacy/compatibility virtual address space layout */
VM_SWAP_TOKEN_TIMEOUT=28, /* default time for token time out */
VM_SWAP_PREFETCH=29, /* int: amount to swap prefetch */
+ VM_DROP_PAGECACHE=30, /* int: nuke lots of pagecache */
};

diff -puN kernel/sysctl.c~drop-pagecache kernel/sysctl.c
--- devel/kernel/sysctl.c~drop-pagecache 2005-12-01 16:41:22.000000000 -0800
+++ devel-akpm/kernel/sysctl.c 2005-12-01 16:41:22.000000000 -0800
@@ -783,6 +783,15 @@ static ctl_table vm_table[] = {
.strategy = &sysctl_intvec,
},
{
+ .ctl_name = VM_DROP_PAGECACHE,
+ .procname = "drop-pagecache",
+ .data = NULL,
+ .maxlen = sizeof(int),
+ .mode = 0644,
+ .proc_handler = drop_pagecache_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 2005-12-01 16:49:06.000000000 -0800
+++ devel-akpm/mm/truncate.c 2005-12-01 16:49:13.000000000 -0800
@@ -256,7 +256,6 @@ 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 2005-12-01 16:58:30.000000000 -0800
+++ devel-akpm/mm/vmscan.c 2005-12-01 17:00:39.000000000 -0800
@@ -181,8 +181,7 @@ 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;
_