From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754762AbdKIVqY (ORCPT ); Thu, 9 Nov 2017 16:46:24 -0500 Received: from www262.sakura.ne.jp ([202.181.97.72]:22612 "EHLO www262.sakura.ne.jp" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754317AbdKIVqW (ORCPT ); Thu, 9 Nov 2017 16:46:22 -0500 To: shakeelb@google.com Cc: minchan@kernel.org, ying.huang@intel.com, mgorman@techsingularity.net, vdavydov.dev@gmail.com, mhocko@kernel.org, gthelen@google.com, hannes@cmpxchg.org, akpm@linux-foundation.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH v2] mm, shrinker: make shrinker_list lockless From: Tetsuo Handa References: <20171108173740.115166-1-shakeelb@google.com> <2940c150-577a-30a8-fac3-cf59a49b84b4@I-love.SAKURA.ne.jp> In-Reply-To: Message-Id: <201711100646.IJH39597.HOtMLJVSFOQFOF@I-love.SAKURA.ne.jp> X-Mailer: Winbiff [Version 2.51 PL2] X-Accept-Language: ja,en,zh Date: Fri, 10 Nov 2017 06:46:19 +0900 Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Shakeel Butt wrote: > > If you can accept serialized register_shrinker()/unregister_shrinker(), > > I think that something like shown below can do it. > > If we assume that we will never do register_shrinker and > unregister_shrinker on the same object in parallel then do we still > need to do msleep & synchronize_rcu() within mutex? Doing register_shrinker() and unregister_shrinker() on the same object in parallel is wrong. This mutex is to ensure that we do not need to worry about ->list.next field. synchronize_rcu() should not be slow. If you want to avoid msleep() with mutex held, you can also apply > > If you want parallel register_shrinker()/unregister_shrinker(), something like > > shown below on top of shown above will do it. change.