From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752479AbdKTS2q (ORCPT ); Mon, 20 Nov 2017 13:28:46 -0500 Received: from mx0a-001b2d01.pphosted.com ([148.163.156.1]:40062 "EHLO mx0a-001b2d01.pphosted.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751902AbdKTS2n (ORCPT ); Mon, 20 Nov 2017 13:28:43 -0500 Date: Mon, 20 Nov 2017 10:28:38 -0800 From: "Paul E. McKenney" To: Tetsuo Handa Cc: hch@infradead.org, mhocko@kernel.org, minchan@kernel.org, ying.huang@intel.com, mgorman@techsingularity.net, vdavydov.dev@gmail.com, hannes@cmpxchg.org, akpm@linux-foundation.org, shakeelb@google.com, gthelen@google.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH 1/2] mm,vmscan: Kill global shrinker lock. Reply-To: paulmck@linux.vnet.ibm.com References: <20171117173521.GA21692@infradead.org> <20171120092526.llj2q3lqbbxwn4g4@dhcp22.suse.cz> <20171120093309.GA19627@infradead.org> <20171120094237.z6h3kx3ne5ld64pl@dhcp22.suse.cz> <20171120104129.GA25042@infradead.org> <201711201956.IIB86978.OFMVFFOJLtOSHQ@I-love.SAKURA.ne.jp> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <201711201956.IIB86978.OFMVFFOJLtOSHQ@I-love.SAKURA.ne.jp> User-Agent: Mutt/1.5.21 (2010-09-15) X-TM-AS-GCONF: 00 x-cbid: 17112018-0036-0000-0000-0000028F7680 X-IBM-SpamModules-Scores: X-IBM-SpamModules-Versions: BY=3.00008100; HX=3.00000241; KW=3.00000007; PH=3.00000004; SC=3.00000240; SDB=6.00948718; UDB=6.00479074; IPR=6.00728999; BA=6.00005702; NDR=6.00000001; ZLA=6.00000005; ZF=6.00000009; ZB=6.00000000; ZP=6.00000000; ZH=6.00000000; ZU=6.00000002; MB=3.00018109; XFM=3.00000015; UTC=2017-11-20 18:28:40 X-IBM-AV-DETECTION: SAVI=unused REMOTE=unused XFE=unused x-cbparentid: 17112018-0037-0000-0000-00004270986C Message-Id: <20171120182838.GU3624@linux.vnet.ibm.com> X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10432:,, definitions=2017-11-20_10:,, signatures=0 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 priorityscore=1501 malwarescore=0 suspectscore=0 phishscore=0 bulkscore=0 spamscore=0 clxscore=1015 lowpriorityscore=0 impostorscore=0 adultscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.0.1-1709140000 definitions=main-1711200247 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, Nov 20, 2017 at 07:56:28PM +0900, Tetsuo Handa wrote: > Christoph Hellwig wrote: > > On Mon, Nov 20, 2017 at 10:42:37AM +0100, Michal Hocko wrote: > > > The patch has been dropped because allnoconfig failed to compile back > > > then http://lkml.kernel.org/r/CAP=VYLr0rPWi1aeuk4w1On9CYRNmnEWwJgGtaX=wEvGaBURtrg@mail.gmail.com > > > I have problem to find the follow up discussion though. The main > > > argument was that SRC is not generally available and so the core > > > kernel should rely on it. > > > > Paul, > > > > isthere any good reason to not use SRCU in the core kernel and > > instead try to reimplement it using atomic counters? > > CONFIG_SRCU was added in order to save system size. There are users who run Linux on very > small systems ( https://www.elinux.org/images/5/52/Status-of-embedded-Linux-2017-09-JJ62.pdf ). > > Also, atomic counters are not mandatory for shrinker case; e.g. > http://lkml.kernel.org/r/201711161956.EBF57883.QFFMOLOVSOHJFt@I-love.SAKURA.ne.jp . CONFIG_SRCU was indeed added in order to shrink single-CPU systems. But many architectures are now requiring SRCU for one reason or another, in more and more situations. So I recently implemented a UP-only Tiny SRCU, which is quite a bit smaller than its scalable counterpart, Tree SRCU: text data bss dec hex filename 983 64 0 1047 417 /tmp/c/kernel/rcu/srcutiny.o text data bss dec hex filename 6844 193 0 7037 1b7d /tmp/b/kernel/rcu/srcutree.o So perhaps it is time to unconditionally enable SRCU? Thanx, Paul