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=-8.5 required=3.0 tests=INCLUDES_PATCH, MAILING_LIST_MULTI,SIGNED_OFF_BY,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 478D5C32789 for ; Fri, 2 Nov 2018 08:56:09 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 002572082D for ; Fri, 2 Nov 2018 08:56:08 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 002572082D 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 S1726356AbeKBSCd (ORCPT ); Fri, 2 Nov 2018 14:02:33 -0400 Received: from mx2.suse.de ([195.135.220.15]:39012 "EHLO mx1.suse.de" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1725843AbeKBSCd (ORCPT ); Fri, 2 Nov 2018 14:02:33 -0400 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 0267DAE8A; Fri, 2 Nov 2018 08:56:06 +0000 (UTC) Date: Fri, 2 Nov 2018 09:55:57 +0100 From: Michal Hocko To: Konstantin Khlebnikov Cc: linux-mm@kvack.org, Andrew Morton , linux-kernel@vger.kernel.org Subject: Re: [PATCH RFC] mm: do not start node_reclaim for page order > MAX_ORDER Message-ID: <20181102081949.GQ23921@dhcp22.suse.cz> References: <154109387197.925352.10499549042420271600.stgit@buzz> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <154109387197.925352.10499549042420271600.stgit@buzz> 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 Thu 01-11-18 20:37:52, Konstantin Khlebnikov wrote: > Page allocator has check in __alloc_pages_slowpath() but nowdays > there is earlier entry point into reclimer without such check: > get_page_from_freelist() -> node_reclaim(). Is the order check so expensive that it would be visible in the fast path? Spreading these MAX_ORDER checks sounds quite fragile to me. > Signed-off-by: Konstantin Khlebnikov > --- > mm/vmscan.c | 6 ++++++ > 1 file changed, 6 insertions(+) > > diff --git a/mm/vmscan.c b/mm/vmscan.c > index 62ac0c488624..52f672420f0b 100644 > --- a/mm/vmscan.c > +++ b/mm/vmscan.c > @@ -4117,6 +4117,12 @@ int node_reclaim(struct pglist_data *pgdat, gfp_t gfp_mask, unsigned int order) > { > int ret; > > + /* > + * Do not scan if allocation will never succeed. > + */ > + if (order >= MAX_ORDER) > + return NODE_RECLAIM_NOSCAN; > + > /* > * Node reclaim reclaims unmapped file backed pages and > * slab pages if we are over the defined limits. > -- Michal Hocko SUSE Labs