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=-5.8 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,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 E855EC28E80 for ; Wed, 3 Mar 2021 17:11:41 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id B08DB64EC4 for ; Wed, 3 Mar 2021 17:11:41 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1385275AbhCCRJl (ORCPT ); Wed, 3 Mar 2021 12:09:41 -0500 Received: from mx2.suse.de ([195.135.220.15]:55366 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1352188AbhCCMy3 (ORCPT ); Wed, 3 Mar 2021 07:54:29 -0500 X-Virus-Scanned: by amavisd-new at test-mx.suse.de DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=suse.com; s=susede1; t=1614774737; h=from:from:reply-to:date:date:message-id:message-id:to:to:cc:cc: mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=Gegs5ccyMsw3DhFe6SxpdxOypLc6ElTbJlXWRgZLM20=; b=VnL6xiqxy/TFJEzZ5fLzJ0yYeROVeHv99xNLRTtEAz5f+tCc6tqxUg+9SZqsoqLQ7N+8TJ YgOCaHlY0mnBbk91Ff3Z+tTXZtB1xO4TmGzX8UIACCAux8Gvf8Rp55sunbVJ78eHPBE3Dm vCOxoBigDQG2u5hxM2EYPiZmT7yXqbo= Received: from relay2.suse.de (unknown [195.135.221.27]) by mx2.suse.de (Postfix) with ESMTP id 7EEA1AD29; Wed, 3 Mar 2021 12:32:17 +0000 (UTC) Date: Wed, 3 Mar 2021 13:32:11 +0100 From: Michal Hocko To: Feng Tang Cc: "linux-mm@kvack.org" , "linux-kernel@vger.kernel.org" , Andrew Morton , Andrea Arcangeli , David Rientjes , Mel Gorman , Mike Kravetz , Randy Dunlap , Vlastimil Babka , "Hansen, Dave" , "Widawsky, Ben" , Andi leen , "Williams, Dan J" Subject: Re: [PATCH v3 RFC 14/14] mm: speedup page alloc for MPOL_PREFERRED_MANY by adding a NO_SLOWPATH gfp bit Message-ID: References: <1614766858-90344-1-git-send-email-feng.tang@intel.com> <1614766858-90344-15-git-send-email-feng.tang@intel.com> <20210303120717.GA16736@shbuild999.sh.intel.com> <20210303121833.GB16736@shbuild999.sh.intel.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20210303121833.GB16736@shbuild999.sh.intel.com> Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed 03-03-21 20:18:33, Feng Tang wrote: > On Wed, Mar 03, 2021 at 08:07:17PM +0800, Tang, Feng wrote: > > Hi Michal, > > > > On Wed, Mar 03, 2021 at 12:39:57PM +0100, Michal Hocko wrote: > > > On Wed 03-03-21 18:20:58, Feng Tang wrote: > > > > When doing broader test, we noticed allocation slowness in one test > > > > case that malloc memory with size which is slightly bigger than free > > > > memory of targeted nodes, but much less then the total free memory > > > > of system. > > > > > > > > The reason is the code enters the slowpath of __alloc_pages_nodemask(), > > > > which takes quite some time. As alloc_pages_policy() will give it a 2nd > > > > try with NULL nodemask, so there is no need to enter the slowpath for > > > > the first try. Add a new gfp bit to skip the slowpath, so that user cases > > > > like this can leverage. > > > > > > > > With it, the malloc in such case is much accelerated as it never enters > > > > the slowpath. > > > > > > > > Adding a new gfp_mask bit is generally not liked, and another idea is to > > > > add another nodemask to struct 'alloc_context', so it has 2: 'preferred-nmask' > > > > and 'fallback-nmask', and they will be tried in turn if not NULL, with > > > > it we can call __alloc_pages_nodemask() only once. > > > > > > Yes, it is very much disliked. Is there any reason why you cannot use > > > GFP_NOWAIT for that purpose? > > > > I did try that at the first place, but it didn't obviously change the slowness. > > I assumed the direct claim was still involved as GFP_NOWAIT only impact kswapd > > reclaim. I assume you haven't really created gfp mask correctly. What was the exact gfp mask you have used? > > One thing I tried which can fix the slowness is: > > + gfp_mask &= ~(__GFP_DIRECT_RECLAIM | __GFP_KSWAPD_RECLAIM); > > which explicitly clears the 2 kinds of reclaim. And I thought it's too > hacky and didn't mention it in the commit log. Clearing __GFP_DIRECT_RECLAIM would be the right way to achieve GFP_NOWAIT semantic. Why would you want to exclude kswapd as well? -- Michal Hocko SUSE Labs