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=-8.2 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS, UNPARSEABLE_RELAY,URIBL_BLOCKED,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 95AF9C17440 for ; Tue, 12 Nov 2019 18:29:57 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 7A79E21783 for ; Tue, 12 Nov 2019 18:29:57 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727022AbfKLS34 (ORCPT ); Tue, 12 Nov 2019 13:29:56 -0500 Received: from out30-130.freemail.mail.aliyun.com ([115.124.30.130]:40889 "EHLO out30-130.freemail.mail.aliyun.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726718AbfKLS34 (ORCPT ); Tue, 12 Nov 2019 13:29:56 -0500 X-Alimail-AntiSpam: AC=PASS;BC=-1|-1;BR=01201311R171e4;CH=green;DM=||false|;FP=0|-1|-1|-1|0|-1|-1|-1;HT=e01e04394;MF=yang.shi@linux.alibaba.com;NM=1;PH=DS;RN=6;SR=0;TI=SMTPD_---0ThvJW5U_1573583388; Received: from US-143344MP.local(mailfrom:yang.shi@linux.alibaba.com fp:SMTPD_---0ThvJW5U_1573583388) by smtp.aliyun-inc.com(127.0.0.1); Wed, 13 Nov 2019 02:29:51 +0800 Subject: Re: [PATCH] mm: migrate: handle freed page at the first place To: Michal Hocko Cc: mgorman@techsingularity.net, vbabka@suse.cz, akpm@linux-foundation.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org References: <1573510165-113395-1-git-send-email-yang.shi@linux.alibaba.com> <20191112080401.GA2763@dhcp22.suse.cz> From: Yang Shi Message-ID: Date: Tue, 12 Nov 2019 10:29:46 -0800 User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.12; rv:52.0) Gecko/20100101 Thunderbird/52.7.0 MIME-Version: 1.0 In-Reply-To: <20191112080401.GA2763@dhcp22.suse.cz> Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 7bit Content-Language: en-US Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 11/12/19 12:04 AM, Michal Hocko wrote: > On Tue 12-11-19 06:09:25, Yang Shi wrote: >> When doing migration if the freed page is met, we just return without >> migrating it since it is pointless to migrate a freed page. But, the >> current code did two things before handling freed page: >> >> 1. Return -ENOMEM if the page is THP and THP migration is not supported. >> 2. Allocate target page unconditionally. >> >> Both makes not too much sense. If we handle freed page at the first place >> we don't have to worry about allocating/freeing target page and split >> THP at all. >> >> For example (worst case) if we are trying to migrate a freed THP without >> THP migration supported, the migrate_pages() would just split the THP then >> retry to migrate base pages one by one by pointless allocating and freeing >> pages, this is just waste of time. >> >> I didn't run into any actual problem with the current code (or I may >> just not notice it yet), it was found by visual inspection. > It would be preferable to accompany a change like this with some actual > numbers. A race with page freeing should be a very rare situation. Maybe > it is not under some workloads but that would better be checked and > documented. I also do not like to do page state changes for THP > migration without a support. I cannot really say this is 100% correct However that THP will not be migrated actually, just will be freed by put_page(). > from top of my head and I do not see a sufficient justification to go > and chase all those tiny details because that is time consuming. > >> Cc: Michal Hocko >> Cc: Mel Gorman >> Cc: Vlastimil Babka >> Signed-off-by: Yang Shi >> --- >> mm/migrate.c | 18 +++++++----------- >> 1 file changed, 7 insertions(+), 11 deletions(-) >> >> diff --git a/mm/migrate.c b/mm/migrate.c >> index 4fe45d1..ef96997 100644 >> --- a/mm/migrate.c >> +++ b/mm/migrate.c >> @@ -1170,13 +1170,6 @@ static ICE_noinline int unmap_and_move(new_page_t get_new_page, >> int rc = MIGRATEPAGE_SUCCESS; >> struct page *newpage; >> >> - if (!thp_migration_supported() && PageTransHuge(page)) >> - return -ENOMEM; >> - >> - newpage = get_new_page(page, private); >> - if (!newpage) >> - return -ENOMEM; >> - >> if (page_count(page) == 1) { >> /* page was freed from under us. So we are done. */ >> ClearPageActive(page); >> @@ -1187,13 +1180,16 @@ static ICE_noinline int unmap_and_move(new_page_t get_new_page, >> __ClearPageIsolated(page); >> unlock_page(page); >> } >> - if (put_new_page) >> - put_new_page(newpage, private); >> - else >> - put_page(newpage); >> goto out; >> } >> >> + if (!thp_migration_supported() && PageTransHuge(page)) >> + return -ENOMEM; >> + >> + newpage = get_new_page(page, private); >> + if (!newpage) >> + return -ENOMEM; >> + >> rc = __unmap_and_move(page, newpage, force, mode); >> if (rc == MIGRATEPAGE_SUCCESS) >> set_page_owner_migrate_reason(newpage, reason); >> -- >> 1.8.3.1 >>