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 200E2C352A3 for ; Fri, 14 Feb 2020 02:55:15 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id CACF9217F4 for ; Fri, 14 Feb 2020 02:55:14 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=kernel.org header.i=@kernel.org header.b="V26bRk+B" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org CACF9217F4 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=linux-foundation.org Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=owner-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix) id 675936B05D8; Thu, 13 Feb 2020 21:55:14 -0500 (EST) Received: by kanga.kvack.org (Postfix, from userid 40) id 626646B05D9; Thu, 13 Feb 2020 21:55:14 -0500 (EST) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 51C7C6B05DA; Thu, 13 Feb 2020 21:55:14 -0500 (EST) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0158.hostedemail.com [216.40.44.158]) by kanga.kvack.org (Postfix) with ESMTP id 3970B6B05D8 for ; Thu, 13 Feb 2020 21:55:14 -0500 (EST) Received: from smtpin10.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay02.hostedemail.com (Postfix) with ESMTP id EA3034417 for ; Fri, 14 Feb 2020 02:55:13 +0000 (UTC) X-FDA: 76487216106.10.show96_84f096f53fe04 X-HE-Tag: show96_84f096f53fe04 X-Filterd-Recvd-Size: 2989 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by imf03.hostedemail.com (Postfix) with ESMTP for ; Fri, 14 Feb 2020 02:55:13 +0000 (UTC) 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 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 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); } ?