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=-10.8 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS autolearn=unavailable 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 CE9BBC432BE for ; Thu, 29 Jul 2021 13:38:50 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id B465160F42 for ; Thu, 29 Jul 2021 13:38:50 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S237635AbhG2Niw (ORCPT ); Thu, 29 Jul 2021 09:38:52 -0400 Received: from smtp-out1.suse.de ([195.135.220.28]:40054 "EHLO smtp-out1.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S237427AbhG2Niu (ORCPT ); Thu, 29 Jul 2021 09:38:50 -0400 Received: from relay2.suse.de (relay2.suse.de [149.44.160.134]) by smtp-out1.suse.de (Postfix) with ESMTP id 29BB7223D7; Thu, 29 Jul 2021 13:38:46 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=suse.com; s=susede1; t=1627565926; 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=pPe7RV+1pqTm3eAjSat/K1TMWuyn28CQYR1rXCWTyW0=; b=A9n4JTjjPzRTsiawg+hSaAZmBRCidZZ2Ctm4t6JRQiuvYyxkvENj5k3WCxEMTKdCzAXnyc rzw94JGO9EUCRcz7K+0UIaTOorQiKM39QXy85AvLGgjLi/nZ6PGrF5hF9pp2B6ruoekwyk NlPlOsZ0gpBeyHKDr/n3Bn7iXZxMnbw= Received: from suse.cz (unknown [10.100.201.86]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by relay2.suse.de (Postfix) with ESMTPS id 9F69EA3B83; Thu, 29 Jul 2021 13:38:45 +0000 (UTC) Date: Thu, 29 Jul 2021 15:38:44 +0200 From: Michal Hocko To: Feng Tang Cc: linux-mm@kvack.org, Andrew Morton , David Rientjes , Dave Hansen , Ben Widawsky , linux-kernel@vger.kernel.org, linux-api@vger.kernel.org, Andrea Arcangeli , Mel Gorman , Mike Kravetz , Randy Dunlap , Vlastimil Babka , Andi Kleen , Dan Williams , ying.huang@intel.com, Dave Hansen Subject: Re: [PATCH v6 1/6] mm/mempolicy: Add MPOL_PREFERRED_MANY for multiple preferred nodes Message-ID: References: <1626077374-81682-1-git-send-email-feng.tang@intel.com> <1626077374-81682-2-git-send-email-feng.tang@intel.com> <20210728141156.GC43486@shbuild999.sh.intel.com> <20210729070918.GA96680@shbuild999.sh.intel.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20210729070918.GA96680@shbuild999.sh.intel.com> Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu 29-07-21 15:09:18, Feng Tang wrote: > On Wed, Jul 28, 2021 at 06:12:21PM +0200, Michal Hocko wrote: > > On Wed 28-07-21 22:11:56, Feng Tang wrote: > > > On Wed, Jul 28, 2021 at 02:31:03PM +0200, Michal Hocko wrote: > > > > [Sorry for a late review] > > > > > > Not at all. Thank you for all your reviews and suggestions from v1 > > > to v6! > > > > > > > On Mon 12-07-21 16:09:29, Feng Tang wrote: > > > > [...] > > > > > @@ -1887,7 +1909,8 @@ nodemask_t *policy_nodemask(gfp_t gfp, struct mempolicy *policy) > > > > > /* Return the node id preferred by the given mempolicy, or the given id */ > > > > > static int policy_node(gfp_t gfp, struct mempolicy *policy, int nd) > > > > > { > > > > > - if (policy->mode == MPOL_PREFERRED) { > > > > > + if (policy->mode == MPOL_PREFERRED || > > > > > + policy->mode == MPOL_PREFERRED_MANY) { > > > > > nd = first_node(policy->nodes); > > > > > } else { > > > > > /* > > > > > > > > Do we really want to have the preferred node to be always the first node > > > > in the node mask? Shouldn't that strive for a locality as well? Existing > > > > callers already prefer numa_node_id() - aka local node - and I belive we > > > > shouldn't just throw that away here. > > > > > > I think it's about the difference of 'local' and 'prefer/perfer-many' > > > policy. There are different kinds of memory HW: HBM(High Bandwidth > > > Memory), normal DRAM, PMEM (Persistent Memory), which have different > > > price, bandwidth, speed etc. A platform may have two, or all three of > > > these types, and there are real use case which want memory comes > > > 'preferred' node/nodes than the local node. > > > > > > And good point for 'local node', if the 'prefer-many' policy's > > > nodemask has local node set, we should pick it han this > > > 'first_node', and the same semantic also applies to the other > > > several places you pointed out. Or do I misunderstand you point? > > > > Yeah. Essentially what I am trying to tell is that for > > MPOL_PREFERRED_MANY you simply want to return the given node without any > > alternation. That node will be used for the fallback zonelist and the > > nodemask would make sure we won't get out of the policy. > > I think I got your point now :) > > With current mainline code, the 'prefer' policy will return the preferred > node. Yes this makes sense as there is only one node. > For 'prefer-many', we would like to keep the similar semantic, that the > preference of node is 'preferred' > 'local' > all other nodes. Yes but which of the preferred nodes you want to start with. Say your nodemask preferring nodes 0 and 2 with the following topology 0 1 2 3 0 10 30 20 30 1 30 10 20 30 2 20 30 10 30 3 30 30 30 10 And say you are running on cpu 1. I believe you want your allocation preferably from node 2 rathern than 0, right? With your approach you would start with node 0 which would be more distant from cpu 1. Also the semantic to give nodes some ordering based on their numbers sounds rather weird to me. The semantic I am proposing is to allocate from prefered nodes in distance order starting from the local node. -- Michal Hocko SUSE Labs