From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-qk0-f198.google.com (mail-qk0-f198.google.com [209.85.220.198]) by kanga.kvack.org (Postfix) with ESMTP id 89FA06B0277 for ; Wed, 4 Jul 2018 10:56:14 -0400 (EDT) Received: by mail-qk0-f198.google.com with SMTP id j189-v6so6490211qkf.0 for ; Wed, 04 Jul 2018 07:56:14 -0700 (PDT) Received: from EUR03-AM5-obe.outbound.protection.outlook.com (mail-eopbgr30136.outbound.protection.outlook.com. [40.107.3.136]) by mx.google.com with ESMTPS id e6-v6si555624qvj.61.2018.07.04.07.56.13 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-SHA bits=128/128); Wed, 04 Jul 2018 07:56:13 -0700 (PDT) Subject: Re: [PATCH v8 14/17] mm: Iterate only over charged shrinkers during memcg shrink_slab() References: <153063036670.1818.16010062622751502.stgit@localhost.localdomain> <153063066653.1818.976035462801487910.stgit@localhost.localdomain> <20180703135813.ed4eef6a4a2df32fa1085e4c@linux-foundation.org> From: Kirill Tkhai Message-ID: <3fca0622-6f70-25eb-b023-2046c52734b7@virtuozzo.com> Date: Wed, 4 Jul 2018 17:56:04 +0300 MIME-Version: 1.0 In-Reply-To: <20180703135813.ed4eef6a4a2df32fa1085e4c@linux-foundation.org> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org List-ID: To: Andrew Morton Cc: vdavydov.dev@gmail.com, 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 03.07.2018 23:58, Andrew Morton wrote: > On Tue, 03 Jul 2018 18:11:06 +0300 Kirill Tkhai wrote: > >> Using the preparations made in previous patches, in case of memcg >> shrink, we may avoid shrinkers, which are not set in memcg's shrinkers >> bitmap. To do that, we separate iterations over memcg-aware and >> !memcg-aware shrinkers, and memcg-aware shrinkers are chosen >> via for_each_set_bit() from the bitmap. In case of big nodes, >> having many isolated environments, this gives significant >> performance growth. See next patches for the details. >> >> Note, that the patch does not respect to empty memcg shrinkers, >> since we never clear the bitmap bits after we set it once. >> Their shrinkers will be called again, with no shrinked objects >> as result. This functionality is provided by next patches. >> >> ... >> >> @@ -541,6 +555,67 @@ static unsigned long do_shrink_slab(struct shrink_control *shrinkctl, >> return freed; >> } >> >> +#ifdef CONFIG_MEMCG_KMEM >> +static unsigned long shrink_slab_memcg(gfp_t gfp_mask, int nid, >> + struct mem_cgroup *memcg, int priority) >> +{ >> + struct memcg_shrinker_map *map; >> + unsigned long freed = 0; >> + int ret, i; >> + >> + if (!memcg_kmem_enabled() || !mem_cgroup_online(memcg)) >> + return 0; >> + >> + if (!down_read_trylock(&shrinker_rwsem)) >> + return 0; > > Why trylock? Presumably some other code path is known to hold the lock > for long periods? Dunno. We take shrinker_rwsem in prealloc_memcg_shrinker() and do memory allocation there. It may result in reclaim under shrinker_rwsem write locked, so we use down_read_trylock() to avoid deadlocks. The first versions of the patchset contained different lock for this function, but it has gone in the process of review. >Comment it, please. OK >> + /* >> + * 1) Caller passes only alive memcg, so map can't be NULL. >> + * 2) shrinker_rwsem protects from maps expanding. >> + */ >> + map = rcu_dereference_protected(memcg->nodeinfo[nid]->shrinker_map, >> + true); >> + BUG_ON(!map); >> + >> + for_each_set_bit(i, map->map, shrinker_nr_max) { >> + struct shrink_control sc = { >> + .gfp_mask = gfp_mask, >> + .nid = nid, >> + .memcg = memcg, >> + }; >> + struct shrinker *shrinker; >> + >> + shrinker = idr_find(&shrinker_idr, i); >> + if (unlikely(!shrinker)) { >> + clear_bit(i, map->map); >> + continue; >> + } >> + BUG_ON(!(shrinker->flags & SHRINKER_MEMCG_AWARE)); > > Fair enough as a development-time sanity check but we shouldn't need > this in production code. Or make it VM_BUG_ON(), at least. OK >> + /* See comment in prealloc_shrinker() */ >> + if (unlikely(list_empty(&shrinker->list))) >> + continue; >> + >> + ret = do_shrink_slab(&sc, shrinker, priority); >> + freed += ret; >> + >> + if (rwsem_is_contended(&shrinker_rwsem)) { >> + freed = freed ? : 1; >> + break; >> + } >> + } >> + >> + up_read(&shrinker_rwsem); >> + return freed; >> +} >