From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-pf0-f200.google.com (mail-pf0-f200.google.com [209.85.192.200]) by kanga.kvack.org (Postfix) with ESMTP id 44B056B05F1 for ; Thu, 10 May 2018 05:54:23 -0400 (EDT) Received: by mail-pf0-f200.google.com with SMTP id e3-v6so911604pfe.15 for ; Thu, 10 May 2018 02:54:23 -0700 (PDT) Received: from EUR03-DB5-obe.outbound.protection.outlook.com (mail-eopbgr40122.outbound.protection.outlook.com. [40.107.4.122]) by mx.google.com with ESMTPS id z9-v6si495586pll.423.2018.05.10.02.54.21 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-SHA bits=128/128); Thu, 10 May 2018 02:54:22 -0700 (PDT) Subject: [PATCH v5 13/13] mm: Clear shrinker bit if there are no objects related to memcg From: Kirill Tkhai Date: Thu, 10 May 2018 12:54:15 +0300 Message-ID: <152594605549.22949.16491037134168999424.stgit@localhost.localdomain> In-Reply-To: <152594582808.22949.8353313986092337675.stgit@localhost.localdomain> References: <152594582808.22949.8353313986092337675.stgit@localhost.localdomain> MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org List-ID: 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 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) 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 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() 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 --- 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() + * + * 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)) {