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 X-Spam-Level: X-Spam-Status: No, score=-11.3 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI,NICE_REPLY_A, SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 autolearn=unavailable autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 7113CC4742C for ; Mon, 2 Nov 2020 13:04:02 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 1F20B223B0 for ; Mon, 2 Nov 2020 13:04:02 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728923AbgKBNEB (ORCPT ); Mon, 2 Nov 2020 08:04:01 -0500 Received: from mx2.suse.de ([195.135.220.15]:50450 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1728655AbgKBNEB (ORCPT ); Mon, 2 Nov 2020 08:04:01 -0500 X-Virus-Scanned: by amavisd-new at test-mx.suse.de Received: from relay2.suse.de (unknown [195.135.221.27]) by mx2.suse.de (Postfix) with ESMTP id 2C106ABAE; Mon, 2 Nov 2020 13:03:59 +0000 (UTC) Subject: Re: [PATCH v3 1/2] mm/compaction: count pages and stop correctly during page isolation. To: Zi Yan , Andrew Morton , linux-mm@kvack.org Cc: Yang Shi , Michal Hocko , Rik van Riel , linux-kernel@vger.kernel.org, stable@vger.kernel.org References: <20201030183809.3616803-1-zi.yan@sent.com> From: Vlastimil Babka Message-ID: <839ec612-1494-c341-302e-585056b2abae@suse.cz> Date: Mon, 2 Nov 2020 14:03:58 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.4.0 MIME-Version: 1.0 In-Reply-To: <20201030183809.3616803-1-zi.yan@sent.com> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 10/30/20 7:38 PM, Zi Yan wrote: > From: Zi Yan > > In isolate_migratepages_block, when cc->alloc_contig is true, we are > able to isolate compound pages, nr_migratepages and nr_isolated did not > count compound pages correctly, causing us to isolate more pages than we > thought. Count compound pages as the number of base pages they contain. > Otherwise, we might be trapped in too_many_isolated while loop, > since the actual isolated pages can go up to > COMPACT_CLUSTER_MAX*512=16384, where COMPACT_CLUSTER_MAX is 32, > since we stop isolation after cc->nr_migratepages reaches to > COMPACT_CLUSTER_MAX. > > In addition, after we fix the issue above, cc->nr_migratepages could > never be equal to COMPACT_CLUSTER_MAX if compound pages are isolated, > thus page isolation could not stop as we intended. Change the isolation > stop condition to >=. > > The issue can be triggered as follows: > In a system with 16GB memory and an 8GB CMA region reserved by > hugetlb_cma, if we first allocate 10GB THPs and mlock them > (so some THPs are allocated in the CMA region and mlocked), reserving > 6 1GB hugetlb pages via > /sys/kernel/mm/hugepages/hugepages-1048576kB/nr_hugepages will get stuck > (looping in too_many_isolated function) until we kill either task. > With the patch applied, oom will kill the application with 10GB THPs and > let hugetlb page reservation finish. > > Fixes: 1da2f328fa64 (“mm,thp,compaction,cma: allow THP migration for CMA allocations”) > Signed-off-by: Zi Yan > Reviewed-by: Yang Shi > Cc: Acked-by: Vlastimil Babka > --- > mm/compaction.c | 8 ++++---- > 1 file changed, 4 insertions(+), 4 deletions(-) > > diff --git a/mm/compaction.c b/mm/compaction.c > index ee1f8439369e..3e834ac402f1 100644 > --- a/mm/compaction.c > +++ b/mm/compaction.c > @@ -1012,8 +1012,8 @@ isolate_migratepages_block(struct compact_control *cc, unsigned long low_pfn, > > isolate_success: > list_add(&page->lru, &cc->migratepages); > - cc->nr_migratepages++; > - nr_isolated++; > + cc->nr_migratepages += compound_nr(page); > + nr_isolated += compound_nr(page); > > /* > * Avoid isolating too much unless this block is being > @@ -1021,7 +1021,7 @@ isolate_migratepages_block(struct compact_control *cc, unsigned long low_pfn, > * or a lock is contended. For contention, isolate quickly to > * potentially remove one source of contention. > */ > - if (cc->nr_migratepages == COMPACT_CLUSTER_MAX && > + if (cc->nr_migratepages >= COMPACT_CLUSTER_MAX && > !cc->rescan && !cc->contended) { > ++low_pfn; > break; > @@ -1132,7 +1132,7 @@ isolate_migratepages_range(struct compact_control *cc, unsigned long start_pfn, > if (!pfn) > break; > > - if (cc->nr_migratepages == COMPACT_CLUSTER_MAX) > + if (cc->nr_migratepages >= COMPACT_CLUSTER_MAX) > break; > } > >