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 CBC4DC4361B for ; Tue, 15 Dec 2020 08:26:39 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 6FAB722273 for ; Tue, 15 Dec 2020 08:26:39 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727051AbgLOI03 (ORCPT ); Tue, 15 Dec 2020 03:26:29 -0500 Received: from mx2.suse.de ([195.135.220.15]:41744 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726217AbgLOI0N (ORCPT ); Tue, 15 Dec 2020 03:26:13 -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=1608020725; 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=1TNK/lVDl1GoAySvXZqTqRJer4+ab+0COZr0xkYRhJo=; b=Yfl8ZaOr/8CH3TmHkGxKWBL32jv4Ay/iX5yt1AX2Lnad+FQsBWC6P+dHPyHZKE3G+7eLyZ 3MSYiZ6RahCBkG+al79V9luYQ+kF9cNtmJaavuZ6Cnfz6jZfr3b5Qmr6iBdAkFmYvQORfq HRt8iwyvv2lmg9+pJqG92OymMBYaRAY= Received: from relay2.suse.de (unknown [195.135.221.27]) by mx2.suse.de (Postfix) with ESMTP id 88FD3AC7F; Tue, 15 Dec 2020 08:25:25 +0000 (UTC) Date: Tue, 15 Dec 2020 09:25:24 +0100 From: Michal Hocko To: Pavel Tatashin Cc: LKML , linux-mm , Andrew Morton , Vlastimil Babka , David Hildenbrand , Oscar Salvador , Dan Williams , Sasha Levin , Tyler Hicks , Joonsoo Kim , mike.kravetz@oracle.com, Steven Rostedt , Ingo Molnar , Jason Gunthorpe , Peter Zijlstra , Mel Gorman , Matthew Wilcox , David Rientjes , John Hubbard , Linux Doc Mailing List Subject: Re: [PATCH v3 3/6] mm: apply per-task gfp constraints in fast path Message-ID: <20201215082524.GK32193@dhcp22.suse.cz> References: <20201211202140.396852-1-pasha.tatashin@soleen.com> <20201211202140.396852-4-pasha.tatashin@soleen.com> <20201214140912.GE32193@dhcp22.suse.cz> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue 15-12-20 00:20:39, Pavel Tatashin wrote: > > Ack to this. > > Thank you. > > > > > But I do not really understand this. All allocation contexts should have > > a proper gfp mask so why do we have to call current_gfp_context here? > > In fact moving the current_gfp_context in the allocator path should have > > made all this games unnecessary. Memcg reclaim path might need some > > careful check because gfp mask is used more creative there but the > > general reclaim paths should be ok. > > > > > diff --git a/mm/vmscan.c b/mm/vmscan.c > > > > Again, why do we need this when the gfp_mask > > > }; > > > > -- > > Hi Michal, > > Beside from __alloc_pages_nodemask(), the current_gfp_context() is > called from the following six functions: > > try_to_free_pages() > try_to_free_mem_cgroup_pages() > __node_reclaim() > __need_fs_reclaim() > alloc_contig_range() > pcpu_alloc() > > As I understand, the idea is that because the allocator now honors > gfp_context values for all paths, the call can be removed from some of > the above functions. I think you are correct. But, at least from a > quick glance, this is not obvious, and is not the case for all of the > above functions. > > For example: > > alloc_contig_range() > __alloc_contig_migrate_range > isolate_migratepages_range > isolate_migratepages_block > /* > * Only allow to migrate anonymous pages in GFP_NOFS context > * because those do not depend on fs locks. > */ > if (!(cc->gfp_mask & __GFP_FS) && page_mapping(page)) > goto isolate_fail; > > If we remove current_gfp_context() from alloc_contig_range(), the > cc->gfp_mask will not be updated with proper __GFP_FS flag. I do not think I was proposing to drop current_gfp_context from alloc_contig_range. ACR needs some work to be properly scoped gfp mask aware. This should be addressed but I do not think think the code works properly now so I wouldn't lose sleep over it in this series. At least __alloc_contig_migrate_range should follow the gfp mask given to alloc_contig_range. > I have studied some other paths, and they are also convoluted. > Therefore, I am worried about performing this optimization in this > series. Dropping current_gfp_context from the reclaim context should be done in a separate patch. I didn't mean to push for this here. All I meant was to simply not touch gfp/zone_idx in the reclaim path. The changelog should call out that the page allocator always provides proper gfp mask. -- Michal Hocko SUSE Labs