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[209.132.183.28]) by mx.google.com with ESMTPS id n204si4021542oif.141.2019.05.28.10.41.41 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Tue, 28 May 2019 10:41:41 -0700 (PDT) Received-SPF: pass (google.com: domain of longman@redhat.com designates 209.132.183.28 as permitted sender) client-ip=209.132.183.28; Authentication-Results: mx.google.com; spf=pass (google.com: domain of longman@redhat.com designates 209.132.183.28 as permitted sender) smtp.mailfrom=longman@redhat.com; dmarc=pass (p=NONE sp=NONE dis=NONE) header.from=redhat.com Received: from smtp.corp.redhat.com (int-mx07.intmail.prod.int.phx2.redhat.com [10.5.11.22]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id 6F89730833AF; Tue, 28 May 2019 17:41:38 +0000 (UTC) Received: from llong.remote.csb (dhcp-17-85.bos.redhat.com [10.18.17.85]) by smtp.corp.redhat.com (Postfix) with ESMTP id 45C4B1019607; Tue, 28 May 2019 17:41:35 +0000 (UTC) Subject: Re: [PATCH v5 5/7] mm: rework non-root kmem_cache lifecycle management To: Vladimir Davydov Cc: Roman Gushchin , Andrew Morton , linux-mm@kvack.org, linux-kernel@vger.kernel.org, kernel-team@fb.com, Johannes Weiner , Michal Hocko , Rik van Riel , Shakeel Butt , Christoph Lameter , cgroups@vger.kernel.org References: <20190521200735.2603003-1-guro@fb.com> <20190521200735.2603003-6-guro@fb.com> <20190528170828.zrkvcdsj3d3jzzzo@esperanza> <96b8a923-49e4-f13e-b1e3-3df4598d849e@redhat.com> <20190528173959.h4hq55b3ajlfpjrk@esperanza> From: Waiman Long Organization: Red Hat Message-ID: <518419c5-ee74-d9a1-c01c-f1a3306d2d34@redhat.com> Date: Tue, 28 May 2019 13:41:34 -0400 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.6.1 MIME-Version: 1.0 In-Reply-To: <20190528173959.h4hq55b3ajlfpjrk@esperanza> Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 7bit Content-Language: en-US X-Scanned-By: MIMEDefang 2.84 on 10.5.11.22 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.44]); Tue, 28 May 2019 17:41:40 +0000 (UTC) X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On 5/28/19 1:39 PM, Vladimir Davydov wrote: > On Tue, May 28, 2019 at 01:37:50PM -0400, Waiman Long wrote: >> On 5/28/19 1:08 PM, Vladimir Davydov wrote: >>>> static void flush_memcg_workqueue(struct kmem_cache *s) >>>> { >>>> + /* >>>> + * memcg_params.dying is synchronized using slab_mutex AND >>>> + * memcg_kmem_wq_lock spinlock, because it's not always >>>> + * possible to grab slab_mutex. >>>> + */ >>>> mutex_lock(&slab_mutex); >>>> + spin_lock(&memcg_kmem_wq_lock); >>>> s->memcg_params.dying = true; >>>> + spin_unlock(&memcg_kmem_wq_lock); >>> I would completely switch from the mutex to the new spin lock - >>> acquiring them both looks weird. >>> >>>> mutex_unlock(&slab_mutex); >>>> >>>> /* >> There are places where the slab_mutex is held and sleeping functions >> like kvzalloc() are called. I understand that taking both mutex and >> spinlocks look ugly, but converting all the slab_mutex critical sections >> to spinlock critical sections will be a major undertaking by itself. So >> I would suggest leaving that for now. > I didn't mean that. I meant taking spin_lock wherever we need to access > the 'dying' flag, even if slab_mutex is held. So that we don't need to > take mutex_lock in flush_memcg_workqueue, where it's used solely for > 'dying' synchronization. OK, that makes sense. Thanks for the clarification. Cheers, Longman