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=-5.5 required=3.0 tests=INCLUDES_PATCH, MAILING_LIST_MULTI,SPF_PASS,URIBL_BLOCKED,USER_AGENT_MUTT 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 859AFC18DF5 for ; Tue, 20 Nov 2018 14:12:12 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 49A6B206BB for ; Tue, 20 Nov 2018 14:12:12 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 49A6B206BB Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=kernel.org Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-kernel-owner@vger.kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728992AbeKUAla (ORCPT ); Tue, 20 Nov 2018 19:41:30 -0500 Received: from mx2.suse.de ([195.135.220.15]:58638 "EHLO mx1.suse.de" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1725995AbeKUAl3 (ORCPT ); Tue, 20 Nov 2018 19:41:29 -0500 X-Virus-Scanned: by amavisd-new at test-mx.suse.de Received: from relay2.suse.de (unknown [195.135.220.254]) by mx1.suse.de (Postfix) with ESMTP id 6043AB082; Tue, 20 Nov 2018 14:12:08 +0000 (UTC) Date: Tue, 20 Nov 2018 15:12:07 +0100 From: Michal Hocko To: "Kirill A. Shutemov" Cc: linux-mm@kvack.org, Andrew Morton , Oscar Salvador , Pavel Tatashin , David Hildenbrand , LKML Subject: Re: [RFC PATCH 3/3] mm, fault_around: do not take a reference to a locked page Message-ID: <20181120141207.GK22247@dhcp22.suse.cz> References: <20181120134323.13007-1-mhocko@kernel.org> <20181120134323.13007-4-mhocko@kernel.org> <20181120140715.mouc7okin3ht5krr@kshutemo-mobl1> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20181120140715.mouc7okin3ht5krr@kshutemo-mobl1> User-Agent: Mutt/1.10.1 (2018-07-13) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue 20-11-18 17:07:15, Kirill A. Shutemov wrote: > On Tue, Nov 20, 2018 at 02:43:23PM +0100, Michal Hocko wrote: > > From: Michal Hocko > > > > filemap_map_pages takes a speculative reference to each page in the > > range before it tries to lock that page. While this is correct it > > also can influence page migration which will bail out when seeing > > an elevated reference count. The faultaround code would bail on > > seeing a locked page so we can pro-actively check the PageLocked > > bit before page_cache_get_speculative and prevent from pointless > > reference count churn. > > Looks fine to me. Thanks for the review. > But please drop a line of comment in the code. As is it might be confusing > for a reader. This? diff --git a/mm/filemap.c b/mm/filemap.c index c76d6a251770..7c4e439a2e85 100644 --- a/mm/filemap.c +++ b/mm/filemap.c @@ -2554,6 +2554,10 @@ void filemap_map_pages(struct vm_fault *vmf, head = compound_head(page); + /* + * Check the locked pages before taking a reference to not + * go in the way of migration. + */ if (PageLocked(head)) goto next; if (!page_cache_get_speculative(head)) -- Michal Hocko SUSE Labs