From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751918AbcB2Nlo (ORCPT ); Mon, 29 Feb 2016 08:41:44 -0500 Received: from mail-wm0-f68.google.com ([74.125.82.68]:35226 "EHLO mail-wm0-f68.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750723AbcB2Nlm (ORCPT ); Mon, 29 Feb 2016 08:41:42 -0500 Date: Mon, 29 Feb 2016 14:41:39 +0100 From: Michal Hocko 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 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: User-Agent: Mutt/1.5.24 (2015-08-30) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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