From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S936791AbdAKI4l (ORCPT ); Wed, 11 Jan 2017 03:56:41 -0500 Received: from outbound-smtp06.blacknight.com ([81.17.249.39]:37040 "EHLO outbound-smtp06.blacknight.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S936708AbdAKI4j (ORCPT ); Wed, 11 Jan 2017 03:56:39 -0500 Date: Wed, 11 Jan 2017 08:56:35 +0000 From: Mel Gorman To: David Rientjes Cc: Andrew Morton , Vlastimil Babka , Michal Hocko , Jonathan Corbet , "Kirill A. Shutemov" , linux-kernel@vger.kernel.org, linux-mm@kvack.org Subject: Re: [patch v2] mm, thp: add new defer+madvise defrag option Message-ID: <20170111085635.vnou5j537lhqyaam@techsingularity.net> References: <20170105101330.bvhuglbbeudubgqb@techsingularity.net> <558ce85c-4cb4-8e56-6041-fc4bce2ee27f@suse.cz> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-15 Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.6.2 (2016-07-01) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Jan 10, 2017 at 04:15:27PM -0800, David Rientjes wrote: > There is no thp defrag option that currently allows MADV_HUGEPAGE regions > to do direct compaction and reclaim while all other thp allocations simply > trigger kswapd and kcompactd in the background and fail immediately. > > The "defer" setting simply triggers background reclaim and compaction for > all regions, regardless of MADV_HUGEPAGE, which makes it unusable for our > userspace where MADV_HUGEPAGE is being used to indicate the application is > willing to wait for work for thp memory to be available. > > The "madvise" setting will do direct compaction and reclaim for these > MADV_HUGEPAGE regions, but does not trigger kswapd and kcompactd in the > background for anybody else. > > For reasonable usage, there needs to be a mesh between the two options. > This patch introduces a fifth mode, "defer+madvise", that will do direct > reclaim and compaction for MADV_HUGEPAGE regions and trigger background > reclaim and compaction for everybody else so that hugepages may be > available in the near future. > > A proposal to allow direct reclaim and compaction for MADV_HUGEPAGE > regions as part of the "defer" mode, making it a very powerful setting and > avoids breaking userspace, was offered: > http://marc.info/?t=148236612700003. This additional mode is a > compromise. > > A second proposal to allow both "defer" and "madvise" to be selected at > the same time was also offered: http://marc.info/?t=148357345300001. > This is possible, but there was a concern that it might break existing > userspaces the parse the output of the defrag mode, so the fifth option > was introduced instead. > > This patch also cleans up the helper function for storing to "enabled" > and "defrag" since the former supports three modes while the latter > supports five and triple_flag_store() was getting unnecessarily messy. > > Signed-off-by: David Rientjes > --- > v2: uses new naming suggested by Vlastimil > (defer+madvise order looks better in > "... defer defer+madvise madvise ...") > > v1 was acked by Mel, and it probably could have been preserved but it was > removed in case there is an issue with the name change. > There isn't Acked-by: Mel Gorman Thanks. -- Mel Gorman SUSE Labs