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 7CF4CC433DB for ; Thu, 4 Mar 2021 13:01:07 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 3EAC964EF9 for ; Thu, 4 Mar 2021 13:01:07 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S240048AbhCDNAf (ORCPT ); Thu, 4 Mar 2021 08:00:35 -0500 Received: from mx2.suse.de ([195.135.220.15]:55656 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S239330AbhCDNA1 (ORCPT ); Thu, 4 Mar 2021 08:00:27 -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=1614862781; 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=4ARETMDmrnoIKUwLwM3yWLvY0xN8oIu75OlSuWmhP6c=; b=YVZipQj4lihqCZsf8NqE3Ye6VPBR+XKX9pzlfuuD1bBuLxbvJz4oPGivveBxKJ90elChtR Mk3sQ7yI/MuCups4BVl+rlnfYeiUf1ZvOakCHzWh0R17Hq3ZvQfLoDBTFl/X6ZGj3YetEz kfz2mbXMP3SiDgMuiNllw11QqRYorvw= Received: from relay2.suse.de (unknown [195.135.221.27]) by mx2.suse.de (Postfix) with ESMTP id 1A12AAAC5; Thu, 4 Mar 2021 12:59:41 +0000 (UTC) Date: Thu, 4 Mar 2021 13:59:40 +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" , 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: <20210303120717.GA16736@shbuild999.sh.intel.com> <20210303121833.GB16736@shbuild999.sh.intel.com> <20210303131832.GB78458@shbuild999.sh.intel.com> <20210303134644.GC78458@shbuild999.sh.intel.com> <20210303163141.v5wu2sfo2zj2qqsw@intel.com> <20210303172250.wbp47skyuf6r37wi@intel.com> <20210304081414.GC43191@shbuild999.sh.intel.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20210304081414.GC43191@shbuild999.sh.intel.com> Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu 04-03-21 16:14:14, Feng Tang wrote: > On Wed, Mar 03, 2021 at 09:22:50AM -0800, Ben Widawsky wrote: > > On 21-03-03 18:14:30, Michal Hocko wrote: > > > On Wed 03-03-21 08:31:41, Ben Widawsky wrote: > > > > On 21-03-03 14:59:35, Michal Hocko wrote: > > > > > On Wed 03-03-21 21:46:44, Feng Tang wrote: > > > > > > On Wed, Mar 03, 2021 at 09:18:32PM +0800, Tang, Feng wrote: > > > > > > > On Wed, Mar 03, 2021 at 01:32:11PM +0100, Michal Hocko wrote: > > > > > > > > On Wed 03-03-21 20:18:33, Feng Tang wrote: > > > > > [...] > > > > > > > > > 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? > > > > > > > > > > > > > > When I tried gfp_mask &= ~__GFP_DIRECT_RECLAIM, the slowness couldn't > > > > > > > be fixed. > > > > > > > > > > > > I just double checked by rerun the test, 'gfp_mask &= ~__GFP_DIRECT_RECLAIM' > > > > > > can also accelerate the allocation much! though is still a little slower than > > > > > > this patch. Seems I've messed some of the tries, and sorry for the confusion! > > > > > > > > > > > > Could this be used as the solution? or the adding another fallback_nodemask way? > > > > > > but the latter will change the current API quite a bit. > > > > > > > > > > I haven't got to the whole series yet. The real question is whether the > > > > > first attempt to enforce the preferred mask is a general win. I would > > > > > argue that it resembles the existing single node preferred memory policy > > > > > because that one doesn't push heavily on the preferred node either. So > > > > > dropping just the direct reclaim mode makes some sense to me. > > > > > > > > > > IIRC this is something I was recommending in an early proposal of the > > > > > feature. > > > > > > > > My assumption [FWIW] is that the usecases we've outlined for multi-preferred > > > > would want more heavy pushing on the preference mask. However, maybe the uapi > > > > could dictate how hard to try/not try. > > > > > > What does that mean and what is the expectation from the kernel to be > > > more or less cast in stone? > > > > > > > (I'm not positive I've understood your question, so correct me if I > > misunderstood) > > > > I'm not sure there is a stone-cast way to define it nor should we. At the very > > least though, something in uapi that has a general mapping to GFP flags > > (specifically around reclaim) for the first round of allocation could make > > sense. > > > > In my head there are 3 levels of request possible for multiple nodes: > > 1. BIND: Those nodes or die. > > 2. Preferred hard: Those nodes and I'm willing to wait. Fallback if impossible. > > 3. Preferred soft: Those nodes but I don't want to wait. > > > > Current UAPI in the series doesn't define a distinction between 2, and 3. As I > > understand the change, Feng is defining the behavior to be #3, which makes #2 > > not an option. I sort of punted on defining it entirely, in the beginning. > > As discussed earlier in the thread, one less hacky solution is to clear > __GFP_DIRECT_RECLAIM bit so that it won't go into direct reclaim, but still > wakeup the kswapd of target nodes and retry, which sits now between 'Preferred hard' > and 'Preferred soft' :) Yes that is what I've had in mind when talking about a lightweight attempt. > For current MPOL_PREFERRED, its semantic is also 'Preferred hard', that it Did you mean to say prefer soft? Because the direct reclaim is attempted only when node reclaim is enabled. > will check free memory of other nodes before entering slowpath waiting. Yes, hence "soft" semantic. -- Michal Hocko SUSE Labs