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From: Kirill Tkhai <ktkhai@virtuozzo.com>
To: akpm@linux-foundation.org, vdavydov.dev@gmail.com,
	shakeelb@google.com, viro@zeniv.linux.org.uk, hannes@cmpxchg.org,
	mhocko@kernel.org, ktkhai@virtuozzo.com, tglx@linutronix.de,
	pombredanne@nexb.com, stummala@codeaurora.org,
	gregkh@linuxfoundation.org, sfr@canb.auug.org.au, guro@fb.com,
	mka@chromium.org, penguin-kernel@I-love.SAKURA.ne.jp,
	chris@chris-wilson.co.uk, longman@redhat.com, minchan@kernel.org,
	ying.huang@intel.com, mgorman@techsingularity.net, jbacik@fb.com,
	linux@roeck-us.net, linux-kernel@vger.kernel.org,
	linux-mm@kvack.org, willy@infradead.org, lirongqing@baidu.com,
	aryabinin@virtuozzo.com
Subject: [PATCH v5 13/13] mm: Clear shrinker bit if there are no objects related to memcg
Date: Thu, 10 May 2018 12:54:15 +0300	[thread overview]
Message-ID: <152594605549.22949.16491037134168999424.stgit@localhost.localdomain> (raw)
In-Reply-To: <152594582808.22949.8353313986092337675.stgit@localhost.localdomain>

To avoid further unneed calls of do_shrink_slab()
for shrinkers, which already do not have any charged
objects in a memcg, their bits have to be cleared.

This patch introduces a lockless mechanism to do that
without races without parallel list lru add. After
do_shrink_slab() returns SHRINK_EMPTY the first time,
we clear the bit and call it once again. Then we restore
the bit, if the new return value is different.

Note, that single smp_mb__after_atomic() in shrink_slab_memcg()
covers two situations:

1)list_lru_add()     shrink_slab_memcg
    list_add_tail()    for_each_set_bit() <--- read bit
                         do_shrink_slab() <--- missed list update (no barrier)
    <MB>                 <MB>
    set_bit()            do_shrink_slab() <--- seen list update

This situation, when the first do_shrink_slab() sees set bit,
but it doesn't see list update (i.e., race with the first element
queueing), is rare. So we don't add <MB> before the first call
of do_shrink_slab() instead of this to do not slow down generic
case. Also, it's need the second call as seen in below in (2).

2)list_lru_add()      shrink_slab_memcg()
    list_add_tail()     ...
    set_bit()           ...
  ...                   for_each_set_bit()
  do_shrink_slab()        do_shrink_slab()
    clear_bit()           ...
  ...                     ...
  list_lru_add()          ...
    list_add_tail()       clear_bit()
    <MB>                  <MB>
    set_bit()             do_shrink_slab()

The barriers guarantees, the second do_shrink_slab()
in the right side task sees list update if really
cleared the bit. This case is drawn in the code comment.

[Results/performance of the patchset]

After the whole patchset applied the below test shows signify
increase of performance:

$echo 1 > /sys/fs/cgroup/memory/memory.use_hierarchy
$mkdir /sys/fs/cgroup/memory/ct
$echo 4000M > /sys/fs/cgroup/memory/ct/memory.kmem.limit_in_bytes
    $for i in `seq 0 4000`; do mkdir /sys/fs/cgroup/memory/ct/$i; echo $$ > /sys/fs/cgroup/memory/ct/$i/cgroup.procs; mkdir -p s/$i; mount -t tmpfs $i s/$i; touch s/$i/file; done

Then, 5 sequential calls of drop caches:
$time echo 3 > /proc/sys/vm/drop_caches

1)Before:
0.00user 13.78system 0:13.78elapsed 99%CPU
0.00user 5.59system 0:05.60elapsed 99%CPU
0.00user 5.48system 0:05.48elapsed 99%CPU
0.00user 8.35system 0:08.35elapsed 99%CPU
0.00user 8.34system 0:08.35elapsed 99%CPU

2)After
0.00user 1.10system 0:01.10elapsed 99%CPU
0.00user 0.00system 0:00.01elapsed 64%CPU
0.00user 0.01system 0:00.01elapsed 82%CPU
0.00user 0.00system 0:00.01elapsed 64%CPU
0.00user 0.01system 0:00.01elapsed 82%CPU

The results show the performance increases at least in 548 times.

Signed-off-by: Kirill Tkhai <ktkhai@virtuozzo.com>
---
 include/linux/memcontrol.h |    2 ++
 mm/vmscan.c                |   19 +++++++++++++++++--
 2 files changed, 19 insertions(+), 2 deletions(-)

diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h
index 436691a66500..82c0bf2d0579 100644
--- a/include/linux/memcontrol.h
+++ b/include/linux/memcontrol.h
@@ -1283,6 +1283,8 @@ static inline void memcg_set_shrinker_bit(struct mem_cgroup *memcg, int nid, int
 
 		rcu_read_lock();
 		map = MEMCG_SHRINKER_MAP(memcg, nid);
+		/* Pairs with smp mb in shrink_slab() */
+		smp_mb__before_atomic();
 		set_bit(nr, map->map);
 		rcu_read_unlock();
 	}
diff --git a/mm/vmscan.c b/mm/vmscan.c
index 7b0075612d73..189b163bef4a 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -586,8 +586,23 @@ static unsigned long shrink_slab_memcg(gfp_t gfp_mask, int nid,
 			continue;
 
 		ret = do_shrink_slab(&sc, shrinker, priority);
-		if (ret == SHRINK_EMPTY)
-			ret = 0;
+		if (ret == SHRINK_EMPTY) {
+			clear_bit(i, map->map);
+			/*
+			 * Pairs with mb in memcg_set_shrinker_bit():
+			 *
+			 * list_lru_add()     shrink_slab_memcg()
+			 *   list_add_tail()    clear_bit()
+			 *   <MB>               <MB>
+			 *   set_bit()          do_shrink_slab()
+			 */
+			smp_mb__after_atomic();
+			ret = do_shrink_slab(&sc, shrinker, priority);
+			if (ret == SHRINK_EMPTY)
+				ret = 0;
+			else
+				memcg_set_shrinker_bit(memcg, nid, i);
+		}
 		freed += ret;
 
 		if (rwsem_is_contended(&shrinker_rwsem)) {

  parent reply	other threads:[~2018-05-10  9:54 UTC|newest]

Thread overview: 33+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-05-10  9:52 [PATCH v5 00/13] Improve shrink_slab() scalability (old complexity was O(n^2), new is O(n)) Kirill Tkhai
2018-05-10  9:52 ` [PATCH v5 01/13] mm: Assign id to every memcg-aware shrinker Kirill Tkhai
2018-05-13  5:15   ` Vladimir Davydov
2018-05-14  9:03     ` Kirill Tkhai
2018-05-15  3:29       ` Vladimir Davydov
2018-05-10  9:52 ` [PATCH v5 02/13] memcg: Move up for_each_mem_cgroup{, _tree} defines Kirill Tkhai
2018-05-10  9:52 ` [PATCH v5 03/13] mm: Assign memcg-aware shrinkers bitmap to memcg Kirill Tkhai
2018-05-13 16:47   ` Vladimir Davydov
2018-05-14  9:34     ` Kirill Tkhai
2018-05-15  3:54       ` Vladimir Davydov
2018-05-10  9:52 ` [PATCH v5 04/13] mm: Refactoring in workingset_init() Kirill Tkhai
2018-05-10  9:52 ` [PATCH v5 05/13] fs: Refactoring in alloc_super() Kirill Tkhai
2018-05-10  9:53 ` [PATCH v5 06/13] fs: Propagate shrinker::id to list_lru Kirill Tkhai
2018-05-13 16:57   ` Vladimir Davydov
2018-05-10  9:53 ` [PATCH v5 07/13] list_lru: Add memcg argument to list_lru_from_kmem() Kirill Tkhai
2018-05-10  9:53 ` [PATCH v5 08/13] list_lru: Pass dst_memcg argument to memcg_drain_list_lru_node() Kirill Tkhai
2018-05-10  9:53 ` [PATCH v5 09/13] list_lru: Pass lru " Kirill Tkhai
2018-05-10  9:53 ` [PATCH v5 10/13] mm: Set bit in memcg shrinker bitmap on first list_lru item apearance Kirill Tkhai
2018-05-15  4:08   ` Vladimir Davydov
2018-05-10  9:53 ` [PATCH v5 11/13] mm: Iterate only over charged shrinkers during memcg shrink_slab() Kirill Tkhai
2018-05-15  5:44   ` Vladimir Davydov
2018-05-15 10:12     ` Kirill Tkhai
2018-05-17  4:33       ` Vladimir Davydov
2018-05-17 11:39         ` Kirill Tkhai
2018-05-15 14:49     ` Kirill Tkhai
2018-05-17  4:16       ` Vladimir Davydov
2018-05-17 11:49         ` Kirill Tkhai
2018-05-17 13:51           ` Vladimir Davydov
2018-05-10  9:54 ` [PATCH v5 12/13] mm: Add SHRINK_EMPTY shrinker methods return value Kirill Tkhai
2018-05-10  9:54 ` Kirill Tkhai [this message]
2018-05-15  5:59   ` [PATCH v5 13/13] mm: Clear shrinker bit if there are no objects related to memcg Vladimir Davydov
2018-05-15  8:55     ` Kirill Tkhai
2018-05-17  4:49       ` Vladimir Davydov

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