From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-ed1-f72.google.com (mail-ed1-f72.google.com [209.85.208.72]) by kanga.kvack.org (Postfix) with ESMTP id CAF068E0001 for ; Tue, 18 Dec 2018 09:29:56 -0500 (EST) Received: by mail-ed1-f72.google.com with SMTP id c53so12854038edc.9 for ; Tue, 18 Dec 2018 06:29:56 -0800 (PST) Received: from outbound-smtp25.blacknight.com (outbound-smtp25.blacknight.com. [81.17.249.193]) by mx.google.com with ESMTPS id k11-v6si1622039ejb.269.2018.12.18.06.29.54 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Tue, 18 Dec 2018 06:29:55 -0800 (PST) Received: from mail.blacknight.com (pemlinmail03.blacknight.ie [81.17.254.16]) by outbound-smtp25.blacknight.com (Postfix) with ESMTPS id 6F4CFB88E0 for ; Tue, 18 Dec 2018 14:29:54 +0000 (GMT) Date: Tue, 18 Dec 2018 14:29:52 +0000 From: Mel Gorman 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: Sender: owner-linux-mm@kvack.org List-ID: 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 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