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=-15.4 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,UNPARSEABLE_RELAY, 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 A1481C4338F for ; Fri, 6 Aug 2021 03:06:52 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 8251460E09 for ; Fri, 6 Aug 2021 03:06:52 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S241485AbhHFDHG (ORCPT ); Thu, 5 Aug 2021 23:07:06 -0400 Received: from out30-132.freemail.mail.aliyun.com ([115.124.30.132]:50697 "EHLO out30-132.freemail.mail.aliyun.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S230127AbhHFDHD (ORCPT ); Thu, 5 Aug 2021 23:07:03 -0400 X-Alimail-AntiSpam: AC=PASS;BC=-1|-1;BR=01201311R181e4;CH=green;DM=||false|;DS=||;FP=0|-1|-1|-1|0|-1|-1|-1;HT=e01e01424;MF=baolin.wang@linux.alibaba.com;NM=1;PH=DS;RN=4;SR=0;TI=SMTPD_---0Ui5guSV_1628219206; Received: from 30.21.164.16(mailfrom:baolin.wang@linux.alibaba.com fp:SMTPD_---0Ui5guSV_1628219206) by smtp.aliyun-inc.com(127.0.0.1); Fri, 06 Aug 2021 11:06:47 +0800 Subject: Re: [PATCH 1/5] mm: migrate: Move the page count validation to the proper place To: Matthew Wilcox Cc: akpm@linux-foundation.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org References: <1f7e1d083864fbb17a20a9c8349d2e8b427e20a3.1628174413.git.baolin.wang@linux.alibaba.com> From: Baolin Wang Message-ID: Date: Fri, 6 Aug 2021 11:07:18 +0800 User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:78.0) Gecko/20100101 Thunderbird/78.12.0 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=gbk; format=flowed Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi Matthew, > On Thu, Aug 05, 2021 at 11:05:56PM +0800, Baolin Wang wrote: >> We've got the expected count for anonymous page or file page by >> expected_page_refs() at the beginning of migrate_page_move_mapping(), >> thus we should move the page count validation a little forward to >> reduce duplicated code. > > Please add an explanation to the changelog for why it's safe to pull > this out from under the i_pages lock. Sure. In folio_migrate_mapping(), we are sure that the migration page was isolated from lru list and locked, so I think there are no race to get the page count without i_pages lock. Please correct me if I missed something else. Thanks. > >> Signed-off-by: Baolin Wang >> --- >> mm/migrate.c | 10 ++++------ >> 1 file changed, 4 insertions(+), 6 deletions(-) >> >> diff --git a/mm/migrate.c b/mm/migrate.c >> index 239b238..5559571 100644 >> --- a/mm/migrate.c >> +++ b/mm/migrate.c >> @@ -386,11 +386,10 @@ int folio_migrate_mapping(struct address_space *mapping, >> int expected_count = expected_page_refs(mapping, &folio->page) + extra_count; >> long nr = folio_nr_pages(folio); >> >> - if (!mapping) { >> - /* Anonymous page without mapping */ >> - if (folio_ref_count(folio) != expected_count) >> - return -EAGAIN; >> + if (folio_ref_count(folio) != expected_count) >> + return -EAGAIN; >> >> + if (!mapping) { >> /* No turning back from here */ >> newfolio->index = folio->index; >> newfolio->mapping = folio->mapping; >> @@ -404,8 +403,7 @@ int folio_migrate_mapping(struct address_space *mapping, >> newzone = folio_zone(newfolio); >> >> xas_lock_irq(&xas); >> - if (folio_ref_count(folio) != expected_count || >> - xas_load(&xas) != folio) { >> + if (xas_load(&xas) != folio) { >> xas_unlock_irq(&xas); >> return -EAGAIN; >> } >> -- >> 1.8.3.1 >> >>