From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-wm0-f49.google.com (mail-wm0-f49.google.com [74.125.82.49]) by kanga.kvack.org (Postfix) with ESMTP id 3B868828E2 for ; Mon, 29 Feb 2016 08:41:42 -0500 (EST) Received: by mail-wm0-f49.google.com with SMTP id l68so37277311wml.0 for ; Mon, 29 Feb 2016 05:41:42 -0800 (PST) Received: from mail-wm0-f66.google.com (mail-wm0-f66.google.com. [74.125.82.66]) by mx.google.com with ESMTPS id y125si20413838wmy.113.2016.02.29.05.41.41 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Mon, 29 Feb 2016 05:41:41 -0800 (PST) Received: by mail-wm0-f66.google.com with SMTP id l68so8281076wml.3 for ; Mon, 29 Feb 2016 05:41:41 -0800 (PST) Date: Mon, 29 Feb 2016 14:41:39 +0100 From: Michal Hocko Subject: Re: [PATCH 2/5] oom reaper: handle mlocked pages Message-ID: <20160229134139.GB16930@dhcp22.suse.cz> References: <1454505240-23446-1-git-send-email-mhocko@kernel.org> <1454505240-23446-3-git-send-email-mhocko@kernel.org> <20160223132157.GD14178@dhcp22.suse.cz> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Sender: owner-linux-mm@kvack.org List-ID: To: Hugh Dickins Cc: David Rientjes , Andrew Morton , Mel Gorman , Tetsuo Handa , Oleg Nesterov , Linus Torvalds , Andrea Argangeli , Rik van Riel , linux-mm@kvack.org, LKML On Sun 28-02-16 19:19:11, Hugh Dickins wrote: > On Tue, 23 Feb 2016, Michal Hocko wrote: > > On Mon 22-02-16 17:36:07, David Rientjes wrote: > > > > > > Are we concerned about munlock_vma_pages_all() taking lock_page() and > > > perhaps stalling forever, the same way it would stall in exit_mmap() for > > > VM_LOCKED vmas, if another thread has locked the same page and is doing an > > > allocation? > > > > This is a good question. I have checked for that particular case > > previously and managed to convinced myself that this is OK(ish). > > munlock_vma_pages_range locks only THP pages to prevent from the > > parallel split-up AFAICS. > > I think you're mistaken on that: there is also the lock_page() > on every page in Phase 2 of __munlock_pagevec(). Ohh, I have missed that one. Thanks for pointing it out! [...] > > Just for the reference this is what I came up with (just compile tested). > > I tried something similar internally (on an earlier kernel). Like > you I've set that work aside for now, there were quicker ways to fix > the issue at hand. But it does continue to offend me that munlock > demands all those page locks: so if you don't get back to it before me, > I shall eventually. > > I didn't understand why you complicated yours with the "enforce" > arg to munlock_vma_pages_range(): why not just trylock in all cases? Well, I have to confess that I am not really sure I understand all the consequences of the locking here. It has always been subtle and weird issues popping up from time to time. So I only wanted to have that change limitted to the oom_reaper. So I would really appreciate if somebody more knowledgeable had a look. We can drop the mlock patch for now. Thanks for looking into this, Hugh! -- 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