From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754169AbcJUG2e (ORCPT ); Fri, 21 Oct 2016 02:28:34 -0400 Received: from mail-lf0-f65.google.com ([209.85.215.65]:34742 "EHLO mail-lf0-f65.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753106AbcJUG2c (ORCPT ); Fri, 21 Oct 2016 02:28:32 -0400 Date: Fri, 21 Oct 2016 08:28:24 +0200 From: Michal Hocko To: Andrew Morton Cc: "ming.ling" , Minchan Kim , Mel Gorman , Vlastimil Babka , Joonsoo Kim , linux-mm@kvack.org, LKML Subject: Re: [PATCH] mm, compaction: fix NR_ISOLATED_* stats for pfn based migration Message-ID: <20161021062823.GA6045@dhcp22.suse.cz> References: <20161019080240.9682-1-mhocko@kernel.org> <20161020201606.2da29e792856a03a0da0adb2@linux-foundation.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20161020201606.2da29e792856a03a0da0adb2@linux-foundation.org> User-Agent: Mutt/1.6.0 (2016-04-01) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu 20-10-16 20:16:06, Andrew Morton wrote: > On Wed, 19 Oct 2016 10:02:40 +0200 Michal Hocko wrote: > > > Since bda807d44454 ("mm: migrate: support non-lru movable page > > migration") isolate_migratepages_block) can isolate !PageLRU pages which > > would acct_isolated account as NR_ISOLATED_*. Accounting these non-lru > > pages NR_ISOLATED_{ANON,FILE} doesn't make any sense and it can misguide > > heuristics based on those counters such as pgdat_reclaimable_pages resp. > > too_many_isolated which would lead to unexpected stalls during the > > direct reclaim without any good reason. Note that > > __alloc_contig_migrate_range can isolate a lot of pages at once. > > > > On mobile devices such as 512M ram android Phone, it may use a big zram > > swap. In some cases zram(zsmalloc) uses too many non-lru but migratedable > > pages, such as: > > > > MemTotal: 468148 kB > > Normal free:5620kB > > Free swap:4736kB > > Total swap:409596kB > > ZRAM: 164616kB(zsmalloc non-lru pages) > > active_anon:60700kB > > inactive_anon:60744kB > > active_file:34420kB > > inactive_file:37532kB > > > > Fix this by only accounting lru pages to NR_ISOLATED_* in > > isolate_migratepages_block right after they were isolated and we still > > know they were on LRU. Drop acct_isolated because it is called after the > > fact and we've lost that information. Batching per-cpu counter doesn't > > make much improvement anyway. Also make sure that we uncharge only LRU > > pages when putting them back on the LRU in putback_movable_pages resp. > > when unmap_and_move migrates the page. > > It isn't worth backporting into 4.8.x? To be honest, I don't know. AFAIK nobody has ever seen any real problem yet. So this is a just-in-case fix. -- Michal Hocko SUSE Labs