From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-lj1-f200.google.com (mail-lj1-f200.google.com [209.85.208.200]) by kanga.kvack.org (Postfix) with ESMTP id 1FB216B0007 for ; Fri, 6 Jul 2018 13:30:31 -0400 (EDT) Received: by mail-lj1-f200.google.com with SMTP id k7-v6so440127ljk.18 for ; Fri, 06 Jul 2018 10:30:31 -0700 (PDT) Received: from mail-sor-f65.google.com (mail-sor-f65.google.com. [209.85.220.65]) by mx.google.com with SMTPS id f84-v6sor2217681lfi.43.2018.07.06.10.30.28 for (Google Transport Security); Fri, 06 Jul 2018 10:30:28 -0700 (PDT) Date: Fri, 6 Jul 2018 20:30:25 +0300 From: Vladimir Davydov Subject: Re: [PATCH v8 05/17] mm: Assign memcg-aware shrinkers bitmap to memcg Message-ID: <20180706173025.nkpq5o2yfdtb7d7x@esperanza> References: <153063036670.1818.16010062622751502.stgit@localhost.localdomain> <153063056619.1818.12550500883688681076.stgit@localhost.localdomain> <20180703135000.b2322ae0e514f028e7941d3c@linux-foundation.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20180703135000.b2322ae0e514f028e7941d3c@linux-foundation.org> Sender: owner-linux-mm@kvack.org List-ID: To: Andrew Morton Cc: Kirill Tkhai , shakeelb@google.com, viro@zeniv.linux.org.uk, hannes@cmpxchg.org, mhocko@kernel.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, 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 On Tue, Jul 03, 2018 at 01:50:00PM -0700, Andrew Morton wrote: > On Tue, 03 Jul 2018 18:09:26 +0300 Kirill Tkhai wrote: > > > Imagine a big node with many cpus, memory cgroups and containers. > > Let we have 200 containers, every container has 10 mounts, > > and 10 cgroups. All container tasks don't touch foreign > > containers mounts. If there is intensive pages write, > > and global reclaim happens, a writing task has to iterate > > over all memcgs to shrink slab, before it's able to go > > to shrink_page_list(). > > > > Iteration over all the memcg slabs is very expensive: > > the task has to visit 200 * 10 = 2000 shrinkers > > for every memcg, and since there are 2000 memcgs, > > the total calls are 2000 * 2000 = 4000000. > > > > So, the shrinker makes 4 million do_shrink_slab() calls > > just to try to isolate SWAP_CLUSTER_MAX pages in one > > of the actively writing memcg via shrink_page_list(). > > I've observed a node spending almost 100% in kernel, > > making useless iteration over already shrinked slab. > > > > This patch adds bitmap of memcg-aware shrinkers to memcg. > > The size of the bitmap depends on bitmap_nr_ids, and during > > memcg life it's maintained to be enough to fit bitmap_nr_ids > > shrinkers. Every bit in the map is related to corresponding > > shrinker id. > > > > Next patches will maintain set bit only for really charged > > memcg. This will allow shrink_slab() to increase its > > performance in significant way. See the last patch for > > the numbers. > > > > ... > > > > --- a/mm/vmscan.c > > +++ b/mm/vmscan.c > > @@ -182,6 +182,11 @@ static int prealloc_memcg_shrinker(struct shrinker *shrinker) > > if (id < 0) > > goto unlock; > > > > + if (memcg_expand_shrinker_maps(id)) { > > + idr_remove(&shrinker_idr, id); > > + goto unlock; > > + } > > + > > if (id >= shrinker_nr_max) > > shrinker_nr_max = id + 1; > > shrinker->id = id; > > This function ends up being a rather sad little thing. > > : static int prealloc_memcg_shrinker(struct shrinker *shrinker) > : { > : int id, ret = -ENOMEM; > : > : down_write(&shrinker_rwsem); > : id = idr_alloc(&shrinker_idr, shrinker, 0, 0, GFP_KERNEL); > : if (id < 0) > : goto unlock; > : > : if (memcg_expand_shrinker_maps(id)) { > : idr_remove(&shrinker_idr, id); > : goto unlock; > : } > : > : if (id >= shrinker_nr_max) > : shrinker_nr_max = id + 1; > : shrinker->id = id; > : ret = 0; > : unlock: > : up_write(&shrinker_rwsem); > : return ret; > : } > > - there's no need to call memcg_expand_shrinker_maps() unless id >= > shrinker_nr_max so why not move the code and avoid calling > memcg_expand_shrinker_maps() in most cases. memcg_expand_shrinker_maps will return immediately if per memcg shrinker maps can accommodate the new id. Since prealloc_memcg_shrinker is definitely not a hot path, I don't see any penalty in calling this function on each prealloc_memcg_shrinker invocation. > > - why aren't we decreasing shrinker_nr_max in > unregister_memcg_shrinker()? That's easy to do, avoids pointless > work in shrink_slab_memcg() and avoids memory waste in future > prealloc_memcg_shrinker() calls. We can shrink the maps, but IMHO it isn't worth the complexity it would introduce, because in my experience if a workload used N mount points (containers, whatever) at some point of its lifetime, it is likely to use the same amount in the future. > > It should be possible to find the highest ID in an IDR tree with a > straightforward descent of the underlying radix tree, but I doubt if > that has been wired up. Otherwise a simple loop in > unregister_memcg_shrinker() would be needed. > >