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 Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 29A4BC001DF for ; Tue, 1 Aug 2023 09:18:35 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S232721AbjHAJSd (ORCPT ); Tue, 1 Aug 2023 05:18:33 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:47838 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S232868AbjHAJRz (ORCPT ); Tue, 1 Aug 2023 05:17:55 -0400 Received: from outbound-smtp27.blacknight.com (outbound-smtp27.blacknight.com [81.17.249.195]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 7B6C235A0 for ; Tue, 1 Aug 2023 02:16:45 -0700 (PDT) Received: from mail.blacknight.com (pemlinmail04.blacknight.ie [81.17.254.17]) by outbound-smtp27.blacknight.com (Postfix) with ESMTPS id 70D83CAD57 for ; Tue, 1 Aug 2023 10:08:14 +0100 (IST) Received: (qmail 25971 invoked from network); 1 Aug 2023 09:08:14 -0000 Received: from unknown (HELO techsingularity.net) (mgorman@techsingularity.net@[84.203.20.191]) by 81.17.254.9 with ESMTPSA (AES256-SHA encrypted, authenticated); 1 Aug 2023 09:08:14 -0000 Date: Tue, 1 Aug 2023 10:08:12 +0100 From: Mel Gorman To: Johannes Weiner Cc: Andrew Morton , Vlastimil Babka , linux-mm@kvack.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH] mm: compaction: fix endless looping over same migrate block Message-ID: <20230801090812.3o6utiufbwhgevom@techsingularity.net> References: <20230731172450.1632195-1-hannes@cmpxchg.org> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-15 Content-Disposition: inline In-Reply-To: <20230731172450.1632195-1-hannes@cmpxchg.org> Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, Jul 31, 2023 at 01:24:50PM -0400, Johannes Weiner wrote: > During stress testing, the following situation was observed: > > 70 root 39 19 0 0 0 R 100.0 0.0 959:29.92 khugepaged > 310936 root 20 0 84416 25620 512 R 99.7 1.5 642:37.22 hugealloc > > Tracing shows isolate_migratepages_block() endlessly looping over the > first block in the DMA zone: > > hugealloc-310936 [001] ..... 237297.415718: mm_compaction_finished: node=0 zone=DMA order=9 ret=no_suitable_page > hugealloc-310936 [001] ..... 237297.415718: mm_compaction_isolate_migratepages: range=(0x1 ~ 0x400) nr_scanned=513 nr_taken=0 > hugealloc-310936 [001] ..... 237297.415718: mm_compaction_finished: node=0 zone=DMA order=9 ret=no_suitable_page > hugealloc-310936 [001] ..... 237297.415718: mm_compaction_isolate_migratepages: range=(0x1 ~ 0x400) nr_scanned=513 nr_taken=0 > hugealloc-310936 [001] ..... 237297.415718: mm_compaction_finished: node=0 zone=DMA order=9 ret=no_suitable_page > hugealloc-310936 [001] ..... 237297.415718: mm_compaction_isolate_migratepages: range=(0x1 ~ 0x400) nr_scanned=513 nr_taken=0 > hugealloc-310936 [001] ..... 237297.415718: mm_compaction_finished: node=0 zone=DMA order=9 ret=no_suitable_page > hugealloc-310936 [001] ..... 237297.415718: mm_compaction_isolate_migratepages: range=(0x1 ~ 0x400) nr_scanned=513 nr_taken=0 > > The problem is that the functions tries to test and set the skip bit > once on the block, to avoid skipping on its own skip-set, using > pageblock_aligned() on the pfn as a test. But because this is the DMA > zone which starts at pfn 1, this is never true for the first block, > and the skip bit isn't set or tested at all. As a result, > fast_find_migrateblock() returns the same pageblock over and over. > > If the pfn isn't pageblock-aligned, also check if it's the start of > the zone to ensure test-and-set-exactly-once on unaligned ranges. > > Thanks to Vlastimil Babka for the help in debugging this. > > Fixes: 90ed667c03fe ("Revert "Revert "mm/compaction: fix set skip in fast_find_migrateblock""") > Signed-off-by: Johannes Weiner Acked-by: Mel Gorman -- Mel Gorman SUSE Labs