[PATCH] mm: do not drain pagevecs for mlock

[Tao Ma]

In 8891d6da, lru_add_drain_all is added to mlock to flush all the per
cpu pagevecs. It makes this system call runs much slower than the
predecessor(For a 16 core Xeon E5620, it is around 20 times). And the
the more cores we have, the more the performance penalty because of the
nasty call to schedule_on_each_cpu.

>From the commit log of 8891d6da we can see that "it isn't must.  but it
reduce the failure of moving to unevictable list.  its failure can rescue
in vmscan later." Christoph Lameter removes the call in mlockall(ML_FUTURE),
So this patch just removes all the call from mlock/mlockall.

Without this patch:
time ./test_mlock -c 100000

real    0m20.566s
user    0m0.074s
sys     0m12.759s

With this patch:
time ./test_mlock -c 100000

real	0m1.675s
user	0m0.049s
sys	0m1.622s

Cc: David Rientjes <rientjes@xxxxxxxxxx>
Cc: Minchan Kim <minchan.kim@xxxxxxxxx>
Cc: KOSAKI Motohiro <kosaki.motohiro@xxxxxxxxxxxxxx>
Cc: Mel Gorman <mel@xxxxxxxxx>
Cc: Johannes Weiner <jweiner@xxxxxxxxxx>
Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Tao Ma <boyu.mt@xxxxxxxxxx>
---
 mm/mlock.c |    5 -----
 1 files changed, 0 insertions(+), 5 deletions(-)

diff --git a/mm/mlock.c b/mm/mlock.c
index 4f4f53b..bb5fc42 100644
--- a/mm/mlock.c
+++ b/mm/mlock.c
@@ -487,8 +487,6 @@ SYSCALL_DEFINE2(mlock, unsigned long, start, size_t, len)
 	if (!can_do_mlock())
 		return -EPERM;
 
-	lru_add_drain_all();	/* flush pagevec */
-
 	down_write(&current->mm->mmap_sem);
 	len = PAGE_ALIGN(len + (start & ~PAGE_MASK));
 	start &= PAGE_MASK;
@@ -557,9 +555,6 @@ SYSCALL_DEFINE1(mlockall, int, flags)
 	if (!can_do_mlock())
 		goto out;
 
-	if (flags & MCL_CURRENT)
-		lru_add_drain_all();	/* flush pagevec */
-
 	down_write(&current->mm->mmap_sem);
 
 	lock_limit = rlimit(RLIMIT_MEMLOCK);
-- 
1.7.4.1

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