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=-15.2 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER,INCLUDES_PATCH, MAILING_LIST_MULTI,NICE_REPLY_A,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED, USER_AGENT_SANE_1 autolearn=ham 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 64C95C433E9 for ; Thu, 28 Jan 2021 14:34:52 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id D382264D9F for ; Thu, 28 Jan 2021 14:34:51 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org D382264D9F Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=suse.cz Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=owner-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix) id 309C16B007B; Thu, 28 Jan 2021 09:34:51 -0500 (EST) Received: by kanga.kvack.org (Postfix, from userid 40) id 2BAF26B007D; Thu, 28 Jan 2021 09:34:51 -0500 (EST) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 1AA366B007E; Thu, 28 Jan 2021 09:34:51 -0500 (EST) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0018.hostedemail.com [216.40.44.18]) by kanga.kvack.org (Postfix) with ESMTP id E69536B007B for ; Thu, 28 Jan 2021 09:34:50 -0500 (EST) Received: from smtpin07.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay01.hostedemail.com (Postfix) with ESMTP id ABE49180AD822 for ; Thu, 28 Jan 2021 14:34:50 +0000 (UTC) X-FDA: 77755430340.07.dress65_54170d3275a0 Received: from filter.hostedemail.com (10.5.16.251.rfc1918.com [10.5.16.251]) by smtpin07.hostedemail.com (Postfix) with ESMTP id 809E51803F79C for ; Thu, 28 Jan 2021 14:34:50 +0000 (UTC) X-HE-Tag: dress65_54170d3275a0 X-Filterd-Recvd-Size: 5080 Received: from mx2.suse.de (mx2.suse.de [195.135.220.15]) by imf41.hostedemail.com (Postfix) with ESMTP for ; Thu, 28 Jan 2021 14:34:49 +0000 (UTC) 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 90049B13F; Thu, 28 Jan 2021 14:34:48 +0000 (UTC) Subject: Re: [PATCH v2] mm/compactoin: Fix misbehaviors of fast_find_migrateblock() To: Wonhyuk Yang , Andrew Morton Cc: Mel Gorman , linux-mm@kvack.org References: <20210128130411.6125-1-vvghjk1234@gmail.com> From: Vlastimil Babka Message-ID: Date: Thu, 28 Jan 2021 15:34:48 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.6.1 MIME-Version: 1.0 In-Reply-To: <20210128130411.6125-1-vvghjk1234@gmail.com> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On 1/28/21 2:04 PM, Wonhyuk Yang wrote: > In the fast_find_migrateblock(), It iterate freelist to find > proper pageblock. But there are some misbehaviors. > > First, if the page we found is equal to cc->migrate_pfn, it > is considered that we didn't found suitable pageblock. Second, > if the loop was terminated because order is less than > PAGE_ALLOC_COSTLY_ORDER, it could be considered that we found > suitable one. Third, if the skip bit is set on the page block > and go continue, it doesn't check the nr_scanned. Fourth, if > the page block's skip bit is set, it check that page block is > the last of list. But it is unnecessary. > > Fixes: 70b44595eafe9 ("mm, compaction: use free lists to quickly locate > a migration source") > > Signed-off-by: Wonhyuk Yang Acked-by: Vlastimil Babka > --- > Changes in v2: > - Follow Vlastimil's suggestions, using bool varable. > - Fix new misbehavior and remove unecessary . > > v1: https://lore.kernel.org/linux-mm/20210123154320.24278-1-vvghjk1234@gmail.com > --- > mm/compaction.c | 27 ++++++++++++--------------- > 1 file changed, 12 insertions(+), 15 deletions(-) > > diff --git a/mm/compaction.c b/mm/compaction.c > index e5acb9714436..8e5cd9d20435 100644 > --- a/mm/compaction.c > +++ b/mm/compaction.c > @@ -1701,6 +1701,7 @@ static unsigned long fast_find_migrateblock(struct compact_control *cc) > unsigned long pfn = cc->migrate_pfn; > unsigned long high_pfn; > int order; > + bool found_block = false; > > /* Skip hints are relied on to avoid repeats on the fast search */ > if (cc->ignore_skip_hint) > @@ -1743,7 +1744,7 @@ static unsigned long fast_find_migrateblock(struct compact_control *cc) > high_pfn = pageblock_start_pfn(cc->migrate_pfn + distance); > > for (order = cc->order - 1; > - order >= PAGE_ALLOC_COSTLY_ORDER && pfn == cc->migrate_pfn && nr_scanned < limit; > + order >= PAGE_ALLOC_COSTLY_ORDER && !found_block && nr_scanned < limit; > order--) { > struct free_area *area = &cc->zone->free_area[order]; > struct list_head *freelist; > @@ -1758,7 +1759,11 @@ static unsigned long fast_find_migrateblock(struct compact_control *cc) > list_for_each_entry(freepage, freelist, lru) { > unsigned long free_pfn; > > - nr_scanned++; > + if (nr_scanned++ >= limit) { > + move_freelist_tail(freelist, freepage); > + break; > + } > + > free_pfn = page_to_pfn(freepage); > if (free_pfn < high_pfn) { > /* > @@ -1767,12 +1772,8 @@ static unsigned long fast_find_migrateblock(struct compact_control *cc) > * the list assumes an entry is deleted, not > * reordered. > */ > - if (get_pageblock_skip(freepage)) { > - if (list_is_last(freelist, &freepage->lru)) > - break; > - > + if (get_pageblock_skip(freepage)) > continue; > - } > > /* Reorder to so a future search skips recent pages */ > move_freelist_tail(freelist, freepage); > @@ -1780,15 +1781,10 @@ static unsigned long fast_find_migrateblock(struct compact_control *cc) > update_fast_start_pfn(cc, free_pfn); > pfn = pageblock_start_pfn(free_pfn); > cc->fast_search_fail = 0; > + found_block = true; > set_pageblock_skip(freepage); > break; > } > - > - if (nr_scanned >= limit) { > - cc->fast_search_fail++; > - move_freelist_tail(freelist, freepage); > - break; > - } > } > spin_unlock_irqrestore(&cc->zone->lock, flags); > } > @@ -1799,9 +1795,10 @@ static unsigned long fast_find_migrateblock(struct compact_control *cc) > * If fast scanning failed then use a cached entry for a page block > * that had free pages as the basis for starting a linear scan. > */ > - if (pfn == cc->migrate_pfn) > + if (!found_block) { > + cc->fast_search_fail++; > pfn = reinit_migrate_pfn(cc); > - > + } > return pfn; > } > >