From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: ARC-Seal: i=1; a=rsa-sha256; t=1521923596; cv=none; d=google.com; s=arc-20160816; b=tJ+7adMeETrbKWcwJ9SiKQLnpOLFVVMarsb1XCXUwtQk+9svhMSX+XyC56bAuO4euQ Y7x5ow2wPevGzuwXXeARlyje6we9EfR35Ig0cWt0r/JAbwArHZNzlAWEV3/q3O7SGxzN LDFRIm1nTRbPpKK6guHkloyhzFxL2Mt5FH+nYkOPH9PhO2NvcjtBVC/LhYENMyrHOf61 VVTSR/gHp8KHZKkA1JisiDfp3oQJhDWau8+q8963Cn0pX7+zJTyasYQLjrxspaqIhJ7u kISgx9PT6ngtCFiOJWLCddDQ7eamH+uuE9suYV/AxPPalANAwqWFEnQnIK9xk2OuztSP eong== ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=arc-20160816; h=in-reply-to:content-disposition:mime-version:references:message-id :subject:cc:to:from:date:dkim-signature:arc-authentication-results; bh=n2eYhm4/zDDtG8JXZ3xBpUn+W+FipIB42ArWSQ85hWg=; b=ri6VvpRlDHxB5R2OZChmR8BkWMDXN3haAA7TzJrAQscpv33l34wNZAH1VsA1mxPavV 6Jw/ADHNCKnZSe9X5ImS4ujY7KQ7C4EdKkaYwoInvkvv7OwkT2oohPL4ChTHpE2NWpB6 yIRmKF8nCx6etQp7A39IV8GmT0fxNxJhyo2G8U1tKoqrmNCzHV4LDB9Bfh0pjYAi+hff YTh8eWLfPLXrXBt96jGVdcRSaITY/GDnBz8eNRMaZTuM0aErMKFABTERiiBDfIxqjx/Q WGRy4tCj87n2lFlnOS9G+ImTjc7b3oQFw77RqHQhGC8mrDw30sQ21pRCvZ2uoDAoKWQw isVw== ARC-Authentication-Results: i=1; mx.google.com; dkim=pass header.i=@gmail.com header.s=20161025 header.b=CRbwWnXj; spf=pass (google.com: domain of vdavydov.dev@gmail.com designates 209.85.220.65 as permitted sender) smtp.mailfrom=vdavydov.dev@gmail.com; dmarc=pass (p=NONE sp=QUARANTINE dis=NONE) header.from=gmail.com Authentication-Results: mx.google.com; dkim=pass header.i=@gmail.com header.s=20161025 header.b=CRbwWnXj; spf=pass (google.com: domain of vdavydov.dev@gmail.com designates 209.85.220.65 as permitted sender) smtp.mailfrom=vdavydov.dev@gmail.com; dmarc=pass (p=NONE sp=QUARANTINE dis=NONE) header.from=gmail.com X-Google-Smtp-Source: AIpwx48HYt+VcqL+ZaU3whhwr+BUQyMNmN1RuNEhc8Biw7PZqoKoE/6KZxE1CluEQbVqZTZvpbwVVw== Date: Sat, 24 Mar 2018 23:33:12 +0300 From: Vladimir Davydov To: Kirill Tkhai 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 Subject: Re: [PATCH 10/10] mm: Clear shrinker bit if there are no objects related to memcg Message-ID: <20180324203312.b2whjgadm7gwby3v@esperanza> References: <152163840790.21546.980703278415599202.stgit@localhost.localdomain> <152163858159.21546.2876185232270486710.stgit@localhost.localdomain> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <152163858159.21546.2876185232270486710.stgit@localhost.localdomain> X-getmail-retrieved-from-mailbox: INBOX X-GMAIL-THRID: =?utf-8?q?1595553705818183633?= X-GMAIL-MSGID: =?utf-8?q?1595852557328779623?= X-Mailing-List: linux-kernel@vger.kernel.org List-ID: 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. > /* > * 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. > 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. > + 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. > + 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. > + } > + freed += ret; > > if (rwsem_is_contended(&shrinker_rwsem)) { > freed = freed ? : 1;