From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-wm0-f69.google.com (mail-wm0-f69.google.com [74.125.82.69]) by kanga.kvack.org (Postfix) with ESMTP id 4256E6B0005 for ; Thu, 28 Jun 2018 17:29:07 -0400 (EDT) Received: by mail-wm0-f69.google.com with SMTP id w138-v6so5629wmw.4 for ; Thu, 28 Jun 2018 14:29:07 -0700 (PDT) Received: from mx0a-001b2d01.pphosted.com (mx0b-001b2d01.pphosted.com. [148.163.158.5]) by mx.google.com with ESMTPS id j10-v6si914549wrh.398.2018.06.28.14.29.04 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Thu, 28 Jun 2018 14:29:05 -0700 (PDT) Received: from pps.filterd (m0098419.ppops.net [127.0.0.1]) by mx0b-001b2d01.pphosted.com (8.16.0.22/8.16.0.22) with SMTP id w5SLT2Cb142616 for ; Thu, 28 Jun 2018 17:29:03 -0400 Received: from e12.ny.us.ibm.com (e12.ny.us.ibm.com [129.33.205.202]) by mx0b-001b2d01.pphosted.com with ESMTP id 2jw7ak8nq1-1 (version=TLSv1.2 cipher=AES256-GCM-SHA384 bits=256 verify=NOT) for ; Thu, 28 Jun 2018 17:29:03 -0400 Received: from localhost by e12.ny.us.ibm.com with IBM ESMTP SMTP Gateway: Authorized Use Only! Violators will be prosecuted for from ; Thu, 28 Jun 2018 17:29:03 -0400 Date: Thu, 28 Jun 2018 14:31:05 -0700 From: "Paul E. McKenney" 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> Message-Id: <20180628213105.GP3593@linux.vnet.ibm.com> Sender: owner-linux-mm@kvack.org List-ID: To: Michal Hocko Cc: Tetsuo Handa , David Rientjes , linux-mm@kvack.org, Andrew Morton , 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