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 D2F0DC4167B for ; Wed, 6 Dec 2023 09:54:13 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1377294AbjLFJyF (ORCPT ); Wed, 6 Dec 2023 04:54:05 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:53948 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1377254AbjLFJyE (ORCPT ); Wed, 6 Dec 2023 04:54:04 -0500 Received: from out30-98.freemail.mail.aliyun.com (out30-98.freemail.mail.aliyun.com [115.124.30.98]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id C9300FA for ; Wed, 6 Dec 2023 01:54:09 -0800 (PST) X-Alimail-AntiSpam: AC=PASS;BC=-1|-1;BR=01201311R201e4;CH=green;DM=||false|;DS=||;FP=0|-1|-1|-1|0|-1|-1|-1;HT=ay29a033018045192;MF=baolin.wang@linux.alibaba.com;NM=1;PH=DS;RN=11;SR=0;TI=SMTPD_---0Vxxc1mm_1701856445; Received: from 30.97.48.44(mailfrom:baolin.wang@linux.alibaba.com fp:SMTPD_---0Vxxc1mm_1701856445) by smtp.aliyun-inc.com; Wed, 06 Dec 2023 17:54:06 +0800 Message-ID: <079610c2-04ed-4495-8eb7-518b04f911f7@linux.alibaba.com> Date: Wed, 6 Dec 2023 17:54:24 +0800 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [RFC PATCH] mm: compaction: avoid fast_isolate_freepages blindly choose improper pageblock To: Barry Song <21cnbao@gmail.com>, akpm@linux-foundation.org, linux-mm@kvack.org Cc: david@redhat.com, shikemeng@huaweicloud.com, willy@infradead.org, mgorman@techsingularity.net, hannes@cmpxchg.org, linux-kernel@vger.kernel.org, Barry Song , Zhanyuan Hu References: <20231129104530.63787-1-v-songbaohua@oppo.com> From: Baolin Wang In-Reply-To: <20231129104530.63787-1-v-songbaohua@oppo.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 11/29/2023 6:45 PM, Barry Song wrote: > Testing shows fast_isolate_freepages can blindly choose an unsuitable > pageblock from time to time particularly while the min mark is used > from XXX path: > if (!page) { > cc->fast_search_fail++; > if (scan_start) { > /* > * Use the highest PFN found above min. If one was > * not found, be pessimistic for direct compaction > * and use the min mark. > */ > if (highest >= min_pfn) { > page = pfn_to_page(highest); > cc->free_pfn = highest; > } else { > if (cc->direct_compaction && pfn_valid(min_pfn)) { /* XXX */ > page = pageblock_pfn_to_page(min_pfn, > min(pageblock_end_pfn(min_pfn), > zone_end_pfn(cc->zone)), > cc->zone); > cc->free_pfn = min_pfn; > } > } > } > } Yes, the min_pfn can be an unsuitable migration target. But I think we can just add the suitable_migration_target() validation into 'min_pfn' case? Since other cases must be suitable target which found from MIGRATE_MOVABLE free list. Something like below: diff --git a/mm/compaction.c b/mm/compaction.c index 01ba298739dd..4e8eb4571909 100644 --- a/mm/compaction.c +++ b/mm/compaction.c @@ -1611,6 +1611,8 @@ static void fast_isolate_freepages(struct compact_control *cc) min(pageblock_end_pfn(min_pfn), zone_end_pfn(cc->zone)), cc->zone); + if (!suitable_migration_target(cc, page)) + page = NULL; cc->free_pfn = min_pfn; } } By the way, I wonder if this patch can improve the efficiency of compaction in your test case? > In contrast, slow path is skipping unsuitable pageblocks in a decent way. > > I don't know if it is an intended design or just an oversight. But > it seems more sensible to skip unsuitable pageblock. > > Reported-by: Zhanyuan Hu > Signed-off-by: Barry Song > --- > mm/compaction.c | 6 ++++++ > 1 file changed, 6 insertions(+) > > diff --git a/mm/compaction.c b/mm/compaction.c > index 01ba298739dd..98c485a25614 100644 > --- a/mm/compaction.c > +++ b/mm/compaction.c > @@ -1625,6 +1625,12 @@ static void fast_isolate_freepages(struct compact_control *cc) > cc->total_free_scanned += nr_scanned; > if (!page) > return; > + /* > + * Otherwise, we can blindly choose an improper pageblock especially > + * while using the min mark > + */ > + if (!suitable_migration_target(cc, page)) > + return; > > low_pfn = page_to_pfn(page); > fast_isolate_around(cc, low_pfn);