From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-ed1-f69.google.com (mail-ed1-f69.google.com [209.85.208.69]) by kanga.kvack.org (Postfix) with ESMTP id 5C20C8E01DC for ; Fri, 14 Dec 2018 16:36:44 -0500 (EST) Received: by mail-ed1-f69.google.com with SMTP id c53so3400077edc.9 for ; Fri, 14 Dec 2018 13:36:44 -0800 (PST) Received: from mx1.suse.de (mx2.suse.de. [195.135.220.15]) by mx.google.com with ESMTPS id k54si2361587edb.369.2018.12.14.13.36.42 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Fri, 14 Dec 2018 13:36:42 -0800 (PST) Subject: Re: [LKP] [mm] ac5b2c1891: vm-scalability.throughput -61.3% regression References: <64a4aec6-3275-a716-8345-f021f6186d9b@suse.cz> <20181204104558.GV23260@techsingularity.net> <20181205204034.GB11899@redhat.com> <20181205233632.GE11899@redhat.com> <20181210044916.GC24097@redhat.com> <0bbf4202-6187-28fb-37b7-da6885b89cce@suse.cz> From: Vlastimil Babka Message-ID: <0700f5c3-66a8-338a-0ba0-2231cc3bb637@suse.cz> Date: Fri, 14 Dec 2018 22:33:42 +0100 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org List-ID: To: David Rientjes Cc: Andrea Arcangeli , Linus Torvalds , mgorman@techsingularity.net, Michal Hocko , ying.huang@intel.com, s.priebe@profihost.ag, Linux List Kernel Mailing , alex.williamson@redhat.com, lkp@01.org, kirill@shutemov.name, Andrew Morton , zi.yan@cs.rutgers.edu, Linux-MM layout On 12/14/18 10:04 PM, David Rientjes wrote: > On Wed, 12 Dec 2018, Vlastimil Babka wrote: ... > Reclaim likely could be deterministically useful if we consider a redesign > of how migration sources and targets are determined in compaction. > > Has anybody tried a migration scanner that isn't linearly based, rather > finding the highest-order free page of the same migratetype, iterating the > pages of its pageblock, and using this to determine whether the actual > migration will be worthwhile or not? Not exactly that AFAIK, but a year ago in my series [1] patch 6 made migration scanner 'prescan' the block of requested order before actually trying to isolate anything for migration. > I could imagine pageblock_skip being > repurposed for this as the heuristic. > > Finding migration targets would be more tricky, but if we iterate the > pages of the pageblock for low-order free pages and find them to be mostly > used, that seems more appropriate than just pushing all memory to the end > of the zone? Agree. That was patch 8/8 of the same series [1]. > It would be interesting to know if anybody has tried using the per-zone > free_area's to determine migration targets and set a bit if it should be > considered a migration source or a migration target. If all pages for a > pageblock are not on free_areas, they are fully used. Repurposing/adding a new pageblock bit was in my mind to help multiple compactors not undo each other's work in the scheme where there's no free page scanner, but I didn't implement it yet. >>> otherwise we fail and defer because it wasn't able >>> to make a hugepage available. >> >> Note that THP fault compaction doesn't actually defer itself, which I >> think is a weakness of the current implementation and hope that patch 3 >> in my series from yesterday [1] can address that. Because defering is >> the general feedback mechanism that we have for suppressing compaction >> (and thus associated reclaim) in cases it fails for any reason, not just >> the one you mention. Instead of inspecting failure conditions in detail, >> which would be costly, it's a simple statistical approach. And when >> compaction is improved to fail less, defering automatically also happens >> less. >> > > I couldn't get the link to work, unfortunately, I don't think the patch > series made it to LKML :/ I do see it archived for linux-mm, though, so > I'll take a look, thanks! Yeah I forgot to Cc: LKML, but you were also in direct To: so you should have received them directly. Also the abovementioned series, but that's year ago. My fault for not returning to it after being done with the Meltdown fun. I hope to do that soon. [1] https://marc.info/?l=linux-mm&m=151315560308753 >> [1] https://lkml.kernel.org/r/20181211142941.20500-1-vbabka@suse.cz >>