From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-pl0-f69.google.com (mail-pl0-f69.google.com [209.85.160.69]) by kanga.kvack.org (Postfix) with ESMTP id D45F76B000A for ; Mon, 26 Mar 2018 11:37:23 -0400 (EDT) Received: by mail-pl0-f69.google.com with SMTP id n11-v6so5026381plp.22 for ; Mon, 26 Mar 2018 08:37:23 -0700 (PDT) Received: from EUR01-VE1-obe.outbound.protection.outlook.com (mail-ve1eur01on0114.outbound.protection.outlook.com. [104.47.1.114]) by mx.google.com with ESMTPS id l6si10155950pgq.562.2018.03.26.08.37.22 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-SHA bits=128/128); Mon, 26 Mar 2018 08:37:22 -0700 (PDT) Subject: Re: [PATCH 10/10] mm: Clear shrinker bit if there are no objects related to memcg References: <152163840790.21546.980703278415599202.stgit@localhost.localdomain> <152163858159.21546.2876185232270486710.stgit@localhost.localdomain> <20180324203312.b2whjgadm7gwby3v@esperanza> From: Kirill Tkhai Message-ID: Date: Mon, 26 Mar 2018 18:37:13 +0300 MIME-Version: 1.0 In-Reply-To: <20180324203312.b2whjgadm7gwby3v@esperanza> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org List-ID: To: Vladimir Davydov Cc: viro@zeniv.linux.org.uk, hannes@cmpxchg.org, mhocko@kernel.org, akpm@linux-foundation.org, 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, hillf.zj@alibaba-inc.com, ying.huang@intel.com, mgorman@techsingularity.net, shakeelb@google.com, jbacik@fb.com, linux@roeck-us.net, linux-kernel@vger.kernel.org, linux-mm@kvack.org, willy@infradead.org On 24.03.2018 23:33, Vladimir Davydov wrote: > On Wed, Mar 21, 2018 at 04:23:01PM +0300, Kirill Tkhai wrote: >> 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 new return value SHRINK_EMPTY, >> which will be used in case of there is no charged >> objects in shrinker. We can't use 0 instead of that, >> as a shrinker may return 0, when it has very small >> amount of objects. >> >> To prevent race with parallel list lru add, we call >> do_shrink_slab() once again, after the bit is cleared. >> So, if there is a new object, we never miss it, and >> the bit will be restored again. >> >> The below test shows significant performance growths >> after using the patchset: >> >> $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 4 drop_caches: >> $time echo 3 > /proc/sys/vm/drop_caches >> >> Times of drop_caches: >> >> *Before (4 iterations)* >> 0.00user 6.80system 0:06.82elapsed 99%CPU >> 0.00user 4.61system 0:04.62elapsed 99%CPU >> 0.00user 4.61system 0:04.61elapsed 99%CPU >> 0.00user 4.61system 0:04.61elapsed 99%CPU >> >> *After (4 iterations)* >> 0.00user 0.93system 0:00.94elapsed 99%CPU >> 0.00user 0.00system 0:00.01elapsed 80%CPU >> 0.00user 0.00system 0:00.01elapsed 80%CPU >> 0.00user 0.00system 0:00.01elapsed 81%CPU >> >> 4.61s/0.01s = 461 times faster. >> >> Signed-off-by: Kirill Tkhai >> --- >> fs/super.c | 3 +++ >> include/linux/shrinker.h | 1 + >> mm/vmscan.c | 21 ++++++++++++++++++--- >> mm/workingset.c | 3 +++ >> 4 files changed, 25 insertions(+), 3 deletions(-) >> >> diff --git a/include/linux/shrinker.h b/include/linux/shrinker.h >> index 24aeed1bc332..b23180deb928 100644 >> --- a/include/linux/shrinker.h >> +++ b/include/linux/shrinker.h >> @@ -34,6 +34,7 @@ struct shrink_control { >> }; >> >> #define SHRINK_STOP (~0UL) >> +#define SHRINK_EMPTY (~0UL - 1) > > Please update the comment below accordingly. Ok >> /* >> * A callback you can register to apply pressure to ageable caches. >> * >> diff --git a/mm/vmscan.c b/mm/vmscan.c >> index e1fd16bc7a9b..1fc05e8bde04 100644 >> --- a/mm/vmscan.c >> +++ b/mm/vmscan.c >> @@ -387,6 +387,7 @@ void set_shrinker_bit(struct mem_cgroup *memcg, int nid, int nr) >> { >> struct shrinkers_map *map = SHRINKERS_MAP(memcg); >> >> + smp_mb__before_atomic(); /* Pairs with mb in shrink_slab() */ > > I don't understand the purpose of this barrier. Please add a comment > explaining why you need it. Ok >> set_bit(nr, map->map[nid]); >> } >> #else /* CONFIG_MEMCG && !CONFIG_SLOB */ >> @@ -568,8 +569,8 @@ static unsigned long do_shrink_slab(struct shrink_control *shrinkctl, >> long scanned = 0, next_deferred; >> >> freeable = shrinker->count_objects(shrinker, shrinkctl); >> - if (freeable == 0) >> - return 0; >> + if (freeable == 0 || freeable == SHRINK_EMPTY) >> + return freeable; >> >> /* >> * copy the current shrinker scan count into a local variable >> @@ -708,6 +709,7 @@ static unsigned long shrink_slab(gfp_t gfp_mask, int nid, >> #if defined(CONFIG_MEMCG) && !defined(CONFIG_SLOB) >> if (!memcg_kmem_enabled() || memcg) { >> struct shrinkers_map *map; >> + unsigned long ret; >> int i; >> >> map = rcu_dereference_protected(SHRINKERS_MAP(memcg), true); >> @@ -724,7 +726,20 @@ static unsigned long shrink_slab(gfp_t gfp_mask, int nid, >> clear_bit(i, map->map[nid]); >> continue; >> } >> - freed += do_shrink_slab(&sc, shrinker, priority); >> + if (!(shrinker->flags & SHRINKER_NUMA_AWARE)) >> + sc.nid = 0; > > Hmm, if my memory doesn't fail, in the previous patch you added a BUG_ON > ensuring that a memcg-aware shrinker must also be numa-aware while here > you still check it. Please remove the BUG_ON or remove this check. > Better remove the BUG_ON, because a memcg-aware shrinker doesn't have to > be numa-aware. Really, we do not introduce new limitations, so it's need to just remove the BUG_ON. Will do in v2. > >> + ret = do_shrink_slab(&sc, shrinker, priority); >> + if (ret == SHRINK_EMPTY) { > > do_shrink_slab() is also called for memcg-unaware shrinkers, you should > probably handle SHRINK_EMPTY there as well. Ok, it looks like we just need to return 0 instead of SHRINK_EMPTY in such cases. >> + clear_bit(i, map->map[nid]); >> + /* pairs with mb in set_shrinker_bit() */ >> + smp_mb__after_atomic(); >> + ret = do_shrink_slab(&sc, shrinker, priority); >> + if (ret == SHRINK_EMPTY) >> + ret = 0; >> + else >> + set_bit(i, map->map[nid]); > > Well, that's definitely a tricky part and hence needs a good comment. > > Anyway, it would be great if we could simplify this part somehow. Ok, I'll add some cleanup preparations for that. >> + } >> + freed += ret; >> >> if (rwsem_is_contended(&shrinker_rwsem)) { >> freed = freed ? : 1; Thanks, Kirill