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 D90A6C433F5 for ; Fri, 10 Sep 2021 08:35:24 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id BF4F161186 for ; Fri, 10 Sep 2021 08:35:24 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S231823AbhIJIgd (ORCPT ); Fri, 10 Sep 2021 04:36:33 -0400 Received: from smtp-out2.suse.de ([195.135.220.29]:57474 "EHLO smtp-out2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S231665AbhIJIga (ORCPT ); Fri, 10 Sep 2021 04:36:30 -0400 Received: from relay2.suse.de (relay2.suse.de [149.44.160.134]) by smtp-out2.suse.de (Postfix) with ESMTP id 918E420203; Fri, 10 Sep 2021 08:35:19 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=suse.com; s=susede1; t=1631262919; 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=byJxGIGEdXY0dNiR3JR/k4UiilB5WnFIjCG84yHjPvA=; b=oMY1GPzbSb4+Nhh3TT6muALj3czRc6RYjO8XFhoTGB2SwjjsTicuFJdPQobspIh+rISUHL eLMWo1ZyXCJA99BQCG2PIGOwS2I4vxmS5p+ttronuYx0OmdLvjSpNOFIp7k0x5sI8qfwPP 4n1ySiHDzUjYigcgBvIWrfsXPmOGYlk= 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 EF7FEA3B99; Fri, 10 Sep 2021 08:35:17 +0000 (UTC) Date: Fri, 10 Sep 2021 10:35:17 +0200 From: Michal Hocko To: Feng Tang Cc: Andrew Morton , David Rientjes , Mel Gorman , Vlastimil Babka , linux-mm@kvack.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH] mm/page_alloc: detect allocation forbidden by cpuset and bail out early Message-ID: References: <1631003150-96935-1-git-send-email-feng.tang@intel.com> <20210908015014.GA28091@shbuild999.sh.intel.com> <20210910074400.GA18707@shbuild999.sh.intel.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20210910074400.GA18707@shbuild999.sh.intel.com> Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri 10-09-21 15:44:00, Feng Tang wrote: > On Wed, Sep 08, 2021 at 09:06:24AM +0200, Michal Hocko wrote: > > On Wed 08-09-21 09:50:14, Feng Tang wrote: > > > On Tue, Sep 07, 2021 at 10:44:32AM +0200, Michal Hocko wrote: > > [...] > > > > While this is a good fix from the functionality POV I believe you can go > > > > a step further. Please add a detection to the cpuset code and complain > > > > to the kernel log if somebody tries to configure movable only cpuset. > > > > Once you have that in place you can easily create a static branch for > > > > cpuset_insane_setup() and have zero overhead for all reasonable > > > > configuration. There shouldn't be any reason to pay a single cpu cycle > > > > to check for something that almost nobody does. > > > > > > > > What do you think? > > > > > > I thought about the implementation, IIUC, the static_branch_enable() is > > > easy, it could be done when cpuset.mems is set with movable only nodes, > > > but disable() is much complexer, > > > > Do we care about disable at all? The point is to not have 99,999999% > > users pay overhead of the check which is irrelevant to them. Once > > somebody wants to use this "creative" setup then paying an extra check > > sounds perfectly sensible to me. If somebody cares enough then the > > disable logic could be implemented. But for now I believe we should be > > OK with only enable case. > > Here is tested draft patch to add the check in cpuset code (the looping > zone code could be improved by adding a for_each_populated_zone_nodemask > macro. > > Thanks, > Feng > > --- > include/linux/cpuset.h | 7 +++++++ > include/linux/mmzone.h | 14 ++++++++++++++ > kernel/cgroup/cpuset.c | 10 ++++++++++ > mm/page_alloc.c | 4 +++- > 4 files changed, 34 insertions(+), 1 deletion(-) > > diff --git a/include/linux/cpuset.h b/include/linux/cpuset.h > index d2b9c41..a434985 100644 > --- a/include/linux/cpuset.h > +++ b/include/linux/cpuset.h > @@ -34,6 +34,8 @@ > */ > extern struct static_key_false cpusets_pre_enable_key; > extern struct static_key_false cpusets_enabled_key; > +extern struct static_key_false cpusets_abnormal_setup_key; > + > static inline bool cpusets_enabled(void) > { > return static_branch_unlikely(&cpusets_enabled_key); > @@ -51,6 +53,11 @@ static inline void cpuset_dec(void) > static_branch_dec_cpuslocked(&cpusets_pre_enable_key); > } > > +static inline bool cpusets_abnormal_check_needed(void) I would go with cpusets_insane_config with a comment explaining what that means. I would also do a pr_info() when the static branch is enabled. [...] > diff --git a/mm/page_alloc.c b/mm/page_alloc.c > index 4e455fa..5728675 100644 > --- a/mm/page_alloc.c > +++ b/mm/page_alloc.c > @@ -4919,7 +4919,9 @@ __alloc_pages_slowpath(gfp_t gfp_mask, unsigned int order, > * any suitable zone to satisfy the request - e.g. non-movable > * GFP_HIGHUSER allocations from MOVABLE nodes only. > */ > - if (cpusets_enabled() && (gfp_mask & __GFP_HARDWALL)) { > + if (cpusets_enabled() && > + cpusets_abnormal_check_needed() && You do not need cpusets_enabled check here. Remember the primary point is to not introduce any branch unless a dubious configuration is in place. > + (gfp_mask & __GFP_HARDWALL)) { > struct zoneref *z = first_zones_zonelist(ac->zonelist, > ac->highest_zoneidx, > &cpuset_current_mems_allowed); > -- > 2.7.4 > -- Michal Hocko SUSE Labs