From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-wm0-f42.google.com (mail-wm0-f42.google.com [74.125.82.42]) by kanga.kvack.org (Postfix) with ESMTP id AE26A6B0254 for ; Thu, 28 Jan 2016 16:55:18 -0500 (EST) Received: by mail-wm0-f42.google.com with SMTP id l66so43764922wml.0 for ; Thu, 28 Jan 2016 13:55:18 -0800 (PST) Received: from mx2.suse.de (mx2.suse.de. [195.135.220.15]) by mx.google.com with ESMTPS id 197si6718940wmf.42.2016.01.28.13.55.17 for (version=TLS1 cipher=ECDHE-RSA-AES128-SHA bits=128/128); Thu, 28 Jan 2016 13:55:17 -0800 (PST) Date: Thu, 28 Jan 2016 22:55:15 +0100 From: Michal Hocko Subject: Re: why do we do ALLOC_WMARK_HIGH before going out_of_memory Message-ID: <20160128215514.GF621@dhcp22.suse.cz> References: <20160128163802.GA15953@dhcp22.suse.cz> <20160128190204.GJ12228@redhat.com> <20160128201123.GB621@dhcp22.suse.cz> <20160128211240.GA4163@cmpxchg.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20160128211240.GA4163@cmpxchg.org> Sender: owner-linux-mm@kvack.org List-ID: To: Johannes Weiner Cc: Andrea Arcangeli , linux-mm@kvack.org, Mel Gorman , David Rientjes , Andrew Morton On Thu 28-01-16 16:12:40, Johannes Weiner wrote: > On Thu, Jan 28, 2016 at 09:11:23PM +0100, Michal Hocko wrote: > > On Thu 28-01-16 20:02:04, Andrea Arcangeli wrote: > > > It's not immediately apparent if there is a new OOM killer upstream > > > logic that would prevent the risk of a second OOM killer invocation > > > despite another OOM killing already happened while we were stuck in > > > reclaim. In absence of that, the high wmark check would be still > > > needed. > > > > Well, my oom detection rework [1] strives to make the OOM detection more > > robust and the retry logic performs the watermark check. So I think the > > last attempt is no longer needed after that patch. I will then remove > > it. > > Hm? I don't have the same conclusion from what Andrea said. > > When you have many allocations racing at the same time, they can all > enter __alloc_pages_may_oom() in quick succession. We don't want a > cavalcade of OOM kills when one could be enough, so we have to make > sure that in between should_alloc_retry() giving up and acquiring the > OOM lock nobody else already issued a kill and released enough memory. > > It's a race window that gets yanked wide open when hundreds of threads > race in __alloc_pages_may_oom(). Your patches don't fix that, AFAICS. Only one task would be allowed to go out_of_memory and all the rest will simply fail on oom_lock trylock and return with NULL. Or am I missing your point? -- Michal Hocko SUSE Labs -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org