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 95FD6C433DB for ; Thu, 18 Feb 2021 16:15:28 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 4D3A064E6F for ; Thu, 18 Feb 2021 16:15:28 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S233232AbhBRQPS (ORCPT ); Thu, 18 Feb 2021 11:15:18 -0500 Received: from mx2.suse.de ([195.135.220.15]:60774 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S231139AbhBRNd6 (ORCPT ); Thu, 18 Feb 2021 08:33:58 -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 A2CF4AF49; Thu, 18 Feb 2021 13:33:09 +0000 (UTC) Date: Thu, 18 Feb 2021 14:32:50 +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: <20210218133250.GA7983@localhost.localdomain> References: <20210217100816.28860-1-osalvador@suse.de> <20210217100816.28860-2-osalvador@suse.de> <20210218100917.GA4842@localhost.localdomain> 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 Thu, Feb 18, 2021 at 01:52:38PM +0100, Michal Hocko wrote: > > 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? > > I would have to double check because hugetlb has a slightly different > expectations from nodemask than the page allocator. The later translates > that to all possible nodes but hugetlb API tries to dereference nodes. > Maybe THIS node special cases it somewhere. Uhm, I do not quite follow here. AFAICS, alloc_fresh_huge_page->alloc_buddy_huge_page does nothing with the nodemask, bur rather with nodes_retry mask. That is done to not retry on a node we failed to allocate a page. Now, alloc_buddy_huge_page calls __alloc_pages_nodemask directly. If my understanding is correct, it is ok to have a null nodemask as __next_zones_zonelist() will go through our own zonelist, since __GFP_THISNODE made us take ZONELIST_NOFALLBACK. Actually, I do not see how passing a non-null nodemask migth have helped there, unless we allow to specify more nodes. > > 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. > > I am not sure I follow. newly allocated pages is unreferenced > unconditionally and the old page is not referenced by this path. Current code is: allocate_a_new_page (new_page's refcount = 1) dissolve_old_page : if fail dissolve_new_page (we cannot dissolve it refcount != 0) put_page(new_page); It should be: allocate_a_new_page (new_page's refcount = 1) put_page(new_page); (new_page's refcount = 0) dissolve_old_page : if fail dissolve_new_page (we can dissolve it as refcount == 0) I hope this clarifies it . -- Oscar Salvador SUSE L3