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=-3.8 required=3.0 tests=BAYES_00, 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 A9D62C433E6 for ; Thu, 18 Feb 2021 11:30:54 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 6325764E3E for ; Thu, 18 Feb 2021 11:30:54 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S231326AbhBRLZN (ORCPT ); Thu, 18 Feb 2021 06:25:13 -0500 Received: from mx2.suse.de ([195.135.220.15]:43712 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S232566AbhBRKKK (ORCPT ); Thu, 18 Feb 2021 05:10:10 -0500 X-Virus-Scanned: by amavisd-new at test-mx.suse.de Received: from relay2.suse.de (unknown [195.135.221.27]) by mx2.suse.de (Postfix) with ESMTP id A42DEADE5; Thu, 18 Feb 2021 10:09:20 +0000 (UTC) Date: Thu, 18 Feb 2021 11:09:17 +0100 From: Oscar Salvador To: Michal Hocko Cc: Andrew Morton , Mike Kravetz , David Hildenbrand , Muchun Song , linux-mm@kvack.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH 1/2] mm: Make alloc_contig_range handle free hugetlb pages Message-ID: <20210218100917.GA4842@localhost.localdomain> References: <20210217100816.28860-1-osalvador@suse.de> <20210217100816.28860-2-osalvador@suse.de> 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 Wed, Feb 17, 2021 at 04:00:11PM +0100, Michal Hocko wrote: > Is this really necessary? dissolve_free_huge_page will take care of this > and the race windown you are covering is really tiny. Probably not, I was trying to shrink to race window as much as possible but the call to dissolve_free_huge_page might be enough. > > + nid = page_to_nid(page); > > + spin_unlock(&hugetlb_lock); > > + > > + /* > > + * Before dissolving the page, we need to allocate a new one, > > + * so the pool remains stable. > > + */ > > + new_page = alloc_fresh_huge_page(h, gfp_mask, nid, nmask, NULL); > > wrt. fallback to other zones, I haven't realized that the primary > usecase is a form of memory offlining (from virt-mem). I am not yet sure > what the proper behavior is in that case but if breaking hugetlb pools, > similar to the normal hotplug operation, is viable then this needs a > special mode. We do not want a random alloc_contig_range user to do the > same. So for starter I would go with __GFP_THISNODE here. Ok, makes sense. __GFP_THISNODE will not allow fallback to other node's zones. Since we only allow the nid the page belongs to, nodemask should be NULL, right? > > + if (!h) > > + /* > > + * The page might have been dissolved from under our feet. > > + * If that is the case, return success as if we dissolved it > > + * ourselves. > > + */ > > + return true; > > nit I would put the comment above the conditin for both cases. It reads > more easily that way. At least without { }. Yes, makes sense. > Other than that I haven't noticed any surprises. I did. The 'put_page' call should be placed above, right after getting the page. Otherwise, refcount == 1 and we will fail to dissolve the new page if we need to (in case old page fails to be dissolved). I already fixed that locally. -- Oscar Salvador SUSE L3