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=-2.2 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,UNPARSEABLE_RELAY,USER_AGENT_SANE_1 autolearn=no 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 61EF8C35242 for ; Fri, 14 Feb 2020 03:58:52 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 2BE7A20848 for ; Fri, 14 Feb 2020 03:58:52 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728527AbgBND6v (ORCPT ); Thu, 13 Feb 2020 22:58:51 -0500 Received: from out30-130.freemail.mail.aliyun.com ([115.124.30.130]:45830 "EHLO out30-130.freemail.mail.aliyun.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1728242AbgBND6v (ORCPT ); Thu, 13 Feb 2020 22:58:51 -0500 X-Alimail-AntiSpam: AC=PASS;BC=-1|-1;BR=01201311R741e4;CH=green;DM=||false|;DS=||;FP=0|-1|-1|-1|0|-1|-1|-1;HT=e01e04400;MF=yang.shi@linux.alibaba.com;NM=1;PH=DS;RN=5;SR=0;TI=SMTPD_---0TpwAdAy_1581652722; Received: from US-143344MP.local(mailfrom:yang.shi@linux.alibaba.com fp:SMTPD_---0TpwAdAy_1581652722) by smtp.aliyun-inc.com(127.0.0.1); Fri, 14 Feb 2020 11:58:44 +0800 Subject: Re: [PATCH] mm: migrate.c: migrate PG_readahead flag To: Andrew Morton Cc: willy@infradead.org, mhocko@suse.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org References: <1581640185-95731-1-git-send-email-yang.shi@linux.alibaba.com> <20200213185511.4660aca17553562d764dc7ea@linux-foundation.org> From: Yang Shi Message-ID: Date: Thu, 13 Feb 2020 19:58:40 -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: <20200213185511.4660aca17553562d764dc7ea@linux-foundation.org> 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 2/13/20 6:55 PM, Andrew Morton wrote: > On Fri, 14 Feb 2020 08:29:45 +0800 Yang Shi wrote: > >> Currently migration code doesn't migrate PG_readahead flag. >> Theoretically this would incur slight performance loss as the >> application might have to ramp its readahead back up again. Even though >> such problem happens, it might be hidden by something else since >> migration is typically triggered by compaction and NUMA balancing, any >> of which should be more noticeable. >> >> Migrate the flag after end_page_writeback() since it may clear >> PG_reclaim flag, which is the same bit as PG_readahead, for the new >> page. >> >> --- a/mm/migrate.c >> +++ b/mm/migrate.c >> @@ -647,6 +647,14 @@ void migrate_page_states(struct page *newpage, struct page *page) >> if (PageWriteback(newpage)) >> end_page_writeback(newpage); >> >> + /* >> + * PG_readahead share the same bit with PG_reclaim, the above >> + * end_page_writeback() may clear PG_readahead mistakenly, so set >> + * the bit after that. >> + */ >> + if (PageReadahead(page)) >> + SetPageReadahead(newpage); >> + >> copy_page_owner(page, newpage); >> > Why not The newpage may not have writeback set, migrating readahead flag should not depend on it. > > if (PageWriteback(newpage)) { > end_page_writeback(newpage); > /* > * PG_readahead share the same bit with PG_reclaim, the above > * end_page_writeback() may clear PG_readahead mistakenly, so > * set the bit after that. > */ > if (PageReadahead(page)) > SetPageReadahead(newpage); > } > > ?