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=-2.2 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_PASS,URIBL_BLOCKED,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 9A243C43141 for ; Thu, 28 Jun 2018 21:29:09 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 55571276CB for ; Thu, 28 Jun 2018 21:29:09 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 55571276CB Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=linux.vnet.ibm.com 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 S1754828AbeF1V3G (ORCPT ); Thu, 28 Jun 2018 17:29:06 -0400 Received: from mx0a-001b2d01.pphosted.com ([148.163.156.1]:36558 "EHLO mx0a-001b2d01.pphosted.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751750AbeF1V3F (ORCPT ); Thu, 28 Jun 2018 17:29:05 -0400 Received: from pps.filterd (m0098409.ppops.net [127.0.0.1]) by mx0a-001b2d01.pphosted.com (8.16.0.22/8.16.0.22) with SMTP id w5SLT21q109831 for ; Thu, 28 Jun 2018 17:29:05 -0400 Received: from e12.ny.us.ibm.com (e12.ny.us.ibm.com [129.33.205.202]) by mx0a-001b2d01.pphosted.com with ESMTP id 2jw62mkyja-1 (version=TLSv1.2 cipher=AES256-GCM-SHA384 bits=256 verify=NOT) for ; Thu, 28 Jun 2018 17:29:04 -0400 Received: from localhost by e12.ny.us.ibm.com with IBM ESMTP SMTP Gateway: Authorized Use Only! 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Violators will be prosecuted; (version=TLSv1/SSLv3 cipher=AES256-GCM-SHA384 bits=256/256) Thu, 28 Jun 2018 17:28:59 -0400 Received: from b01ledav003.gho.pok.ibm.com (b01ledav003.gho.pok.ibm.com [9.57.199.108]) by b01cxnp23032.gho.pok.ibm.com (8.14.9/8.14.9/NCO v10.0) with ESMTP id w5SLSwgE19333594 (version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-GCM-SHA384 bits=256 verify=FAIL); Thu, 28 Jun 2018 21:28:58 GMT Received: from b01ledav003.gho.pok.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id 4AE2FB2065; Thu, 28 Jun 2018 17:28:49 -0400 (EDT) Received: from b01ledav003.gho.pok.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id 2CFB9B2064; Thu, 28 Jun 2018 17:28:49 -0400 (EDT) Received: from paulmck-ThinkPad-W541 (unknown [9.70.82.159]) by b01ledav003.gho.pok.ibm.com (Postfix) with ESMTP; Thu, 28 Jun 2018 17:28:49 -0400 (EDT) Received: by paulmck-ThinkPad-W541 (Postfix, from userid 1000) id B5D3116C5F24; Thu, 28 Jun 2018 14:31:05 -0700 (PDT) Date: Thu, 28 Jun 2018 14:31:05 -0700 From: "Paul E. McKenney" To: Michal Hocko Cc: Tetsuo Handa , David Rientjes , linux-mm@kvack.org, Andrew Morton , linux-kernel@vger.kernel.org Subject: Re: [PATCH] mm,oom: Bring OOM notifier callbacks to outside of OOM killer. Reply-To: paulmck@linux.vnet.ibm.com References: <1529493638-6389-1-git-send-email-penguin-kernel@I-love.SAKURA.ne.jp> <20180621073142.GA10465@dhcp22.suse.cz> <2d8c3056-1bc2-9a32-d745-ab328fd587a1@i-love.sakura.ne.jp> <20180626170345.GA3593@linux.vnet.ibm.com> <20180627072207.GB32348@dhcp22.suse.cz> <20180627143125.GW3593@linux.vnet.ibm.com> <20180628113942.GD32348@dhcp22.suse.cz> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20180628113942.GD32348@dhcp22.suse.cz> User-Agent: Mutt/1.5.21 (2010-09-15) X-TM-AS-GCONF: 00 x-cbid: 18062821-0060-0000-0000-000002840703 X-IBM-SpamModules-Scores: X-IBM-SpamModules-Versions: BY=3.00009273; HX=3.00000241; KW=3.00000007; PH=3.00000004; SC=3.00000266; SDB=6.01053715; UDB=6.00540296; IPR=6.00831637; MB=3.00021913; MTD=3.00000008; XFM=3.00000015; UTC=2018-06-28 21:29:02 X-IBM-AV-DETECTION: SAVI=unused REMOTE=unused XFE=unused x-cbparentid: 18062821-0061-0000-0000-0000459C13F1 Message-Id: <20180628213105.GP3593@linux.vnet.ibm.com> X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10434:,, definitions=2018-06-28_08:,, signatures=0 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 priorityscore=1501 malwarescore=0 suspectscore=2 phishscore=0 bulkscore=0 spamscore=0 clxscore=1015 lowpriorityscore=0 mlxscore=0 impostorscore=0 mlxlogscore=999 adultscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.0.1-1806210000 definitions=main-1806280237 Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Jun 28, 2018 at 01:39:42PM +0200, Michal Hocko wrote: > On Wed 27-06-18 07:31:25, Paul E. McKenney wrote: > > On Wed, Jun 27, 2018 at 09:22:07AM +0200, Michal Hocko wrote: > > > On Tue 26-06-18 10:03:45, Paul E. McKenney wrote: > > > [...] > > > > 3. Something else? > > > > > > How hard it would be to use a different API than oom notifiers? E.g. a > > > shrinker which just kicks all the pending callbacks if the reclaim > > > priority reaches low values (e.g. 0)? > > > > Beats me. What is a shrinker? ;-) > > This is a generich mechanism to reclaim memory that is not on standard > LRU lists. Lwn.net surely has some nice coverage (e.g. > https://lwn.net/Articles/548092/). "In addition, there is little agreement over what a call to a shrinker really means or how the called subsystem should respond." ;-) Is this set up using register_shrinker() in mm/vmscan.c? I am guessing that the many mentions of shrinker in DRM are irrelevant. If my guess is correct, the API seems a poor fit for RCU. I can produce an approximate number of RCU callbacks for ->count_objects(), but a given callback might free a lot of memory or none at all. Plus, to actually have ->scan_objects() free them before returning, I would need to use something like rcu_barrier(), which might involve longer delays than desired. Or am I missing something here? > > More seriously, could you please point me at an exemplary shrinker > > use case so I can see what is involved? > > Well, I am not really sure what is the objective of the oom notifier to > point you to the right direction. IIUC you just want to kick callbacks > to be handled sooner under a heavy memory pressure, right? How is that > achieved? Kick a worker? That is achieved by enqueuing a non-lazy callback on each CPU's callback list, but only for those CPUs having non-empty lists. This causes CPUs with lists containing only lazy callbacks to be more aggressive, in particular, it prevents such CPUs from hanging out idle for seconds at a time while they have callbacks on their lists. The enqueuing happens via an IPI to the CPU in question. Thanx, Paul