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[213.151.95.130]) by smtp.gmail.com with ESMTPSA id c2sm15761600wrp.46.2019.12.06.02.09.01 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 06 Dec 2019 02:09:01 -0800 (PST) Date: Fri, 6 Dec 2019 11:09:00 +0100 From: Michal Hocko To: Dave Chinner Cc: Andrey Ryabinin , Pavel Tikhomirov , Andrew Morton , linux-kernel@vger.kernel.org, cgroups@vger.kernel.org, linux-mm@kvack.org, Johannes Weiner , Vladimir Davydov , Roman Gushchin , Shakeel Butt , Chris Down , Yang Shi , Tejun Heo , Thomas Gleixner , "Kirill A . Shutemov" , Konstantin Khorenko , Kirill Tkhai , Trond Myklebust , Anna Schumaker , "J. Bruce Fields" , Chuck Lever , linux-nfs@vger.kernel.org, Alexander Viro , linux-fsdevel@vger.kernel.org Subject: Re: [PATCH] mm: fix hanging shrinker management on long do_shrink_slab Message-ID: <20191206100900.GM28317@dhcp22.suse.cz> References: <20191129214541.3110-1-ptikhomirov@virtuozzo.com> <4e2d959a-0b0e-30aa-59b4-8e37728e9793@virtuozzo.com> <20191206020953.GS2695@dread.disaster.area> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20191206020953.GS2695@dread.disaster.area> User-Agent: Mutt/1.10.1 (2018-07-13) 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 Fri 06-12-19 13:09:53, Dave Chinner wrote: > [please cc me on future shrinker infrastructure modifications] > > On Mon, Dec 02, 2019 at 07:36:03PM +0300, Andrey Ryabinin wrote: > > > > On 11/30/19 12:45 AM, Pavel Tikhomirov wrote: > > > We have a problem that shrinker_rwsem can be held for a long time for > > > read in shrink_slab, at the same time any process which is trying to > > > manage shrinkers hangs. > > > > > > The shrinker_rwsem is taken in shrink_slab while traversing shrinker_list. > > > It tries to shrink something on nfs (hard) but nfs server is dead at > > > these moment already and rpc will never succeed. Generally any shrinker > > > can take significant time to do_shrink_slab, so it's a bad idea to hold > > > the list lock here. > > registering/unregistering a shrinker is not a performance critical > task. We have had a bug report from production system which stumbled over a long [u]nmount which was stuck on a shrinker {un}register path waiting for the lock. This wouldn't be a big deal most of the time but [u]mount were part of the login session in this case. This was on an older distribution kernel and e496612c5130 ("mm: do not stall register_shrinker()") helped a bit but not really for shrinkers that take a lot of time. > If a shrinker is blocking for a long time, then we need to > work to fix the shrinker implementation because blocking is a much > bigger problem than just register/unregister. Absolutely agreed here. -- Michal Hocko SUSE Labs