From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-2.5 required=3.0 tests=MAILING_LIST_MULTI,SPF_PASS, USER_AGENT_MUTT autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id D28E1C46460 for ; Thu, 9 Aug 2018 07:14:26 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 8B79621B31 for ; Thu, 9 Aug 2018 07:14:26 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 8B79621B31 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=kernel.org Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-kernel-owner@vger.kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728862AbeHIJhw (ORCPT ); Thu, 9 Aug 2018 05:37:52 -0400 Received: from mx2.suse.de ([195.135.220.15]:44262 "EHLO mx1.suse.de" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1728056AbeHIJhw (ORCPT ); Thu, 9 Aug 2018 05:37:52 -0400 X-Virus-Scanned: by amavisd-new at test-mx.suse.de Received: from relay1.suse.de (unknown [195.135.220.254]) by mx1.suse.de (Postfix) with ESMTP id 87CACAEC0; Thu, 9 Aug 2018 07:14:21 +0000 (UTC) Date: Thu, 9 Aug 2018 09:14:18 +0200 From: Michal Hocko To: Kirill Tkhai Cc: akpm@linux-foundation.org, gregkh@linuxfoundation.org, rafael@kernel.org, viro@zeniv.linux.org.uk, darrick.wong@oracle.com, paulmck@linux.vnet.ibm.com, josh@joshtriplett.org, rostedt@goodmis.org, mathieu.desnoyers@efficios.com, jiangshanlai@gmail.com, hughd@google.com, shuah@kernel.org, robh@kernel.org, ulf.hansson@linaro.org, aspriel@gmail.com, vivek.gautam@codeaurora.org, robin.murphy@arm.com, joe@perches.com, heikki.krogerus@linux.intel.com, sfr@canb.auug.org.au, vdavydov.dev@gmail.com, chris@chris-wilson.co.uk, penguin-kernel@I-love.SAKURA.ne.jp, aryabinin@virtuozzo.com, willy@infradead.org, ying.huang@intel.com, shakeelb@google.com, jbacik@fb.com, mingo@kernel.org, mhiramat@kernel.org, linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org, linux-mm@kvack.org Subject: Re: [PATCH RFC v2 02/10] mm: Make shrink_slab() lockless Message-ID: <20180809071418.GA24884@dhcp22.suse.cz> References: <153365347929.19074.12509495712735843805.stgit@localhost.localdomain> <153365626605.19074.16202958374930777592.stgit@localhost.localdomain> <591d2063-0511-103d-bef6-dd35f55afe32@virtuozzo.com> <4ceb948c-7ce7-0db3-17d8-82ef1e6e47cc@virtuozzo.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <4ceb948c-7ce7-0db3-17d8-82ef1e6e47cc@virtuozzo.com> User-Agent: Mutt/1.10.1 (2018-07-13) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed 08-08-18 16:20:54, Kirill Tkhai wrote: > [Added two more places needed srcu_dereference(). All ->shrinker_map > dereferences must be under SRCU, and this v2 adds missed in previous] > > The patch makes shrinker list and shrinker_idr SRCU-safe > for readers. This requires synchronize_srcu() on finalize > stage unregistering stage, which waits till all parallel > shrink_slab() are finished > > Note, that patch removes rwsem_is_contended() checks from > the code, and this does not result in delays during > registration, since there is no waiting at all. Unregistration > case may be optimized by splitting unregister_shrinker() > in tho stages, and this is made in next patches. > > Also, keep in mind, that in case of SRCU is not allowed > to make unconditional (which is done in previous patch), > it is possible to use percpu_rw_semaphore instead of it. > percpu_down_read() will be used in shrink_slab_memcg() > and in shrink_slab(), and consecutive calls > > percpu_down_write(percpu_rwsem); > percpu_up_write(percpu_rwsem); > > will be used instead of synchronize_srcu(). An obvious question. Why didn't you go that way? What are pros/cons of both approaches? -- Michal Hocko SUSE Labs