From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-2.5 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_PASS,USER_AGENT_MUTT autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id A10F2C43387 for ; Tue, 18 Dec 2018 14:29:59 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 7B6C421871 for ; Tue, 18 Dec 2018 14:29:59 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727127AbeLRO36 (ORCPT ); Tue, 18 Dec 2018 09:29:58 -0500 Received: from outbound-smtp04.blacknight.com ([81.17.249.35]:39850 "EHLO outbound-smtp04.blacknight.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726541AbeLRO34 (ORCPT ); Tue, 18 Dec 2018 09:29:56 -0500 Received: from mail.blacknight.com (pemlinmail03.blacknight.ie [81.17.254.16]) by outbound-smtp04.blacknight.com (Postfix) with ESMTPS id 7388598ACF for ; Tue, 18 Dec 2018 14:29:54 +0000 (UTC) Received: (qmail 17733 invoked from network); 18 Dec 2018 14:29:54 -0000 Received: from unknown (HELO techsingularity.net) (mgorman@techsingularity.net@[37.228.229.96]) by 81.17.254.9 with ESMTPSA (AES256-SHA encrypted, authenticated); 18 Dec 2018 14:29:54 -0000 Date: Tue, 18 Dec 2018 14:29:52 +0000 From: Mel Gorman To: Vlastimil Babka Cc: Linux-MM , David Rientjes , Andrea Arcangeli , Linus Torvalds , Michal Hocko , ying.huang@intel.com, kirill@shutemov.name, Andrew Morton , Linux List Kernel Mailing Subject: Re: [PATCH 09/14] mm, compaction: Ignore the fragmentation avoidance boost for isolation and compaction Message-ID: <20181218142952.GL29005@techsingularity.net> References: <20181214230310.572-1-mgorman@techsingularity.net> <20181214230310.572-10-mgorman@techsingularity.net> <20181218135156.GK29005@techsingularity.net> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-15 Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.10.1 (2018-07-13) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Dec 18, 2018 at 02:58:33PM +0100, Vlastimil Babka wrote: > On 12/18/18 2:51 PM, Mel Gorman wrote: > > On Tue, Dec 18, 2018 at 01:36:42PM +0100, Vlastimil Babka wrote: > >> On 12/15/18 12:03 AM, Mel Gorman wrote: > >>> When pageblocks get fragmented, watermarks are artifically boosted to pages > >>> are reclaimed to avoid further fragmentation events. However, compaction > >>> is often either fragmentation-neutral or moving movable pages away from > >>> unmovable/reclaimable pages. As the actual watermarks are preserved, > >>> allow compaction to ignore the boost factor. > >> > >> Right, I should have realized that when reviewing the boost patch. I > >> think it would be useful to do the same change in > >> __compaction_suitable() as well. Compaction has its own "gap". > >> > > > > That gap is somewhat static though so I'm a bit more wary of it. However, > > Well, watermark boost is dynamic, but based on allocations stealing from > other migratetypes, not reflecting compaction chances of success. > True. > > the check in __isolate_free_page looks too agressive. We isolate in > > units of COMPACT_CLUSTER_MAX yet the watermark check there is based on > > the allocation request. That means for THP that we check if 512 pages > > can be allocated when only somewhere between 1 and 32 is needed for that > > compaction cycle to complete. Adjusting that might be more appropriate? > > AFAIU the code in __isolate_free_page() reflects that if there's less > than 512 free pages gap, we might form a high-order page for THP but > won't be able to allocate it afterwards due to watermark. Yeah but it used to be a lot more important when watermark checking for high-orders was very different. Now, if the watermark is met for order-0 and a large enough free page is allocated, the allocation succeeds so it's a lot less relevant than it used to be. kswapd will still run in the background for order-0 if necessary so a heavy watermark check there doesn't really help. -- Mel Gorman SUSE Labs