From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754847AbbCMXo0 (ORCPT ); Fri, 13 Mar 2015 19:44:26 -0400 Received: from mx1.redhat.com ([209.132.183.28]:56271 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751080AbbCMXoZ (ORCPT ); Fri, 13 Mar 2015 19:44:25 -0400 Message-ID: <55037631.3010402@redhat.com> Date: Fri, 13 Mar 2015 19:43:45 -0400 From: Rik van Riel User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:31.0) Gecko/20100101 Thunderbird/31.4.0 MIME-Version: 1.0 To: David Rientjes , Eric B Munson CC: Andrew Morton , Vlastimil Babka , Thomas Gleixner , Christoph Lameter , Peter Zijlstra , Mel Gorman , Michal Hocko , linux-mm@kvack.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH V5] Allow compaction of unevictable pages References: <1426267597-25811-1-git-send-email-emunson@akamai.com> <550332CE.7040404@redhat.com> <20150313190915.GA12589@akamai.com> In-Reply-To: Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 03/13/2015 07:18 PM, David Rientjes wrote: > On Fri, 13 Mar 2015, Eric B Munson wrote: > >>>> --- a/mm/compaction.c >>>> +++ b/mm/compaction.c >>>> @@ -1046,6 +1046,8 @@ typedef enum { >>>> ISOLATE_SUCCESS, /* Pages isolated, migrate */ >>>> } isolate_migrate_t; >>>> >>>> +int sysctl_compact_unevictable; >>>> + >>>> /* >>>> * Isolate all pages that can be migrated from the first suitable block, >>>> * starting at the block pointed to by the migrate scanner pfn within >>> >>> I suspect that the use cases where users absolutely do not want >>> unevictable pages migrated are special cases, and it may make >>> sense to enable sysctl_compact_unevictable by default. >> >> Given that sysctl_compact_unevictable=0 is the way the kernel behaves >> now and the push back against always enabling compaction on unevictable >> pages, I left the default to be the behavior as it is today. I agree >> that this is likely the minority case, but I'd really like Peter Z or >> someone else from real time to say that they are okay with the default >> changing. >> > > It would be really disappointing to not enable this by default for !rt > kernels. We haven't migrated mlocked pages in the past by way of memory > compaction because it can theoretically result in consistent minor page > faults, but I haven't yet heard a !rt objection to enabling this. > > If the rt patchset is going to carry a patch to disable this It does not have to carry a patch to disable something that can be disabled at run time. The smaller the realtime patchset has to be, the better. -- All rights reversed