Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754049AbcDKLYJ (ORCPT ); Mon, 11 Apr 2016 07:24:09 -0400 Received: from mail-wm0-f68.google.com ([74.125.82.68]:33353 "EHLO mail-wm0-f68.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753799AbcDKLYH (ORCPT ); Mon, 11 Apr 2016 07:24:07 -0400 Date: Mon, 11 Apr 2016 13:24:04 +0200 From: Michal Hocko To: Vlastimil Babka Cc: Andrew Morton , Linus Torvalds , Johannes Weiner , Mel Gorman , David Rientjes , Tetsuo Handa , Joonsoo Kim , Hillf Danton , linux-mm@kvack.org, LKML Subject: Re: [PATCH 05/11] mm, compaction: distinguish COMPACT_DEFERRED from COMPACT_SKIPPED Message-ID: <20160411112404.GE23157@dhcp22.suse.cz> References: <1459855533-4600-1-git-send-email-mhocko@kernel.org> <1459855533-4600-6-git-send-email-mhocko@kernel.org> <570B843C.8050608@suse.cz> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <570B843C.8050608@suse.cz> 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 Content-Length: 1771 Lines: 46 On Mon 11-04-16 13:02:20, Vlastimil Babka wrote: > On 04/05/2016 01:25 PM, Michal Hocko wrote: > >From: Michal Hocko > > > >try_to_compact_pages can currently return COMPACT_SKIPPED even when the > >compaction is defered for some zone just because zone DMA is skipped > >in 99% of cases due to watermark checks. This makes COMPACT_DEFERRED > >basically unusable for the page allocator as a feedback mechanism. > > > >Make sure we distinguish those two states properly and switch their > >ordering in the enum. This would mean that the COMPACT_SKIPPED will be > >returned only when all eligible zones are skipped. > > > >This shouldn't introduce any functional change. > > Hmm, really? __alloc_pages_direct_compact() does distinguish > COMPACT_DEFERRED, and sets *deferred compaction, so ultimately this is some > change for THP allocations? Hmm, you are right. In cases where we would return COMPACTION_SKIPED even though there is a zone which would really like to tell us COMPACT_DEFERRED then we would previously did __alloc_pages_direct_reclaim and then bail out for THP which do not have __GFP_REPEAT while now we would recognize DEFERRED and bail out without the direct reclaim. So there is a functional change. Adnrew, could you drop the sentence about no functional change and replace it by the following? " As a result COMPACT_DEFERRED handling for THP in __alloc_pages_slowpath will be more precise and we would bail out rather than reclaim. " > Also there's no mention of COMPACT_INACTIVE in the changelog (which indeed > isn't functional change, but might surprise somebody). > > >Signed-off-by: Michal Hocko > > Patch itself is OK. > > Acked-by: Vlastimil Babka Thanks! -- Michal Hocko SUSE Labs