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=-0.8 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE, SPF_PASS 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 EF387C3B194 for ; Fri, 14 Feb 2020 02:55:15 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id BC4E72187F for ; Fri, 14 Feb 2020 02:55:15 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1581648915; bh=lQDKYAfbCVYkA0WiWbRnkihwJDNeJ9WI1ZHWRFRZfp4=; h=Date:From:To:Cc:Subject:In-Reply-To:References:List-ID:From; b=jpaJSIiiL4E5ip2TVPG5RGRWCfN86xZT+wFwjUKA62GdssH8epQmSgqhn2/LGhJpx JBAXEr+fsrziayfeieNYJ8T5jsR1vZ2wshZdhQz2B2Cchswtf4Rg+vSGHdhEjyPE9R XchjSwoK2ce0JmZLc1JVcpWfzAstOjDoA7tMInZQ= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728335AbgBNCzP (ORCPT ); Thu, 13 Feb 2020 21:55:15 -0500 Received: from mail.kernel.org ([198.145.29.99]:37000 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727604AbgBNCzO (ORCPT ); Thu, 13 Feb 2020 21:55:14 -0500 Received: from localhost.localdomain (c-73-231-172-41.hsd1.ca.comcast.net [73.231.172.41]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id 718BB2168B; Fri, 14 Feb 2020 02:55:12 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1581648912; bh=lQDKYAfbCVYkA0WiWbRnkihwJDNeJ9WI1ZHWRFRZfp4=; h=Date:From:To:Cc:Subject:In-Reply-To:References:From; b=V26bRk+BUYMdbQqNQyDqSi8eyS8yH4pDIs4smYhZ2SbGazHJkvd++D105I185t9G8 WPwtRBVxjpFV7sXn55HriYsdol54A6FxY9NVI5h5DEjOzaTPFk/o1w1gUiLCBE4m7D Or7O57tp9EiQk8Bgv0HtYmDVDG42qJo707k+2UdQ= Date: Thu, 13 Feb 2020 18:55:11 -0800 From: Andrew Morton To: Yang Shi Cc: willy@infradead.org, mhocko@suse.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH] mm: migrate.c: migrate PG_readahead flag Message-Id: <20200213185511.4660aca17553562d764dc7ea@linux-foundation.org> In-Reply-To: <1581640185-95731-1-git-send-email-yang.shi@linux.alibaba.com> References: <1581640185-95731-1-git-send-email-yang.shi@linux.alibaba.com> X-Mailer: Sylpheed 3.5.1 (GTK+ 2.24.31; x86_64-pc-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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 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); } ?