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=-2.3 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 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 50F40CA9EC5 for ; Wed, 30 Oct 2019 14:02:25 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 24B2320856 for ; Wed, 30 Oct 2019 14:02:25 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726759AbfJ3OCY (ORCPT ); Wed, 30 Oct 2019 10:02:24 -0400 Received: from smtp2.axis.com ([195.60.68.18]:26087 "EHLO smtp2.axis.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726328AbfJ3OCX (ORCPT ); Wed, 30 Oct 2019 10:02:23 -0400 IronPort-SDR: A6r/sRAgNcgUX6PPp549V7VnqRa+RPsV8Fgd5Ru+gJt5wm1+/Sadm+GxmQVl2XjiGjx+G3z7YQ XTVBPDQVArlEmWjORPnItJ6Lae0eZOWyNcIg1u5SF2X7bETQvczeZ/LzWt02wZ3DXAK3+tG9Ti dLDTINRcTZjDYjo76olwlpc8ZIKyxMkbc6m37TnfYz/ZIO5Ai0GClfE9RElV/B6zjTCAlUkKoZ 3M+ungPUzRNzzcmBJgVdCqPpATxq6sZ9436l2dLaNlfn+Fza0GiP+L8HKNtz+u7aUcy0cTcnqa nNI= X-IronPort-AV: E=Sophos;i="5.68,247,1569276000"; d="scan'208";a="1925617" X-Axis-User: NO X-Axis-NonUser: YES X-Virus-Scanned: Debian amavisd-new at bes.se.axis.com Date: Wed, 30 Oct 2019 15:02:16 +0100 From: Vincent Whitchurch To: Michal Hocko Cc: "akpm@linux-foundation.org" , "osalvador@suse.de" , "linux-mm@kvack.org" , "linux-kernel@vger.kernel.org" Subject: Re: [PATCH] mm/sparse: Consistently do not zero memmap Message-ID: <20191030140216.i26n22asgafckfxy@axis.com> References: <20191030131122.8256-1-vincent.whitchurch@axis.com> <20191030132958.GD31513@dhcp22.suse.cz> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20191030132958.GD31513@dhcp22.suse.cz> User-Agent: NeoMutt/20170113 (1.7.2) X-TM-AS-GCONF: 00 Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Oct 30, 2019 at 02:29:58PM +0100, Michal Hocko wrote: > On Wed 30-10-19 14:11:22, Vincent Whitchurch wrote: > > (I noticed this because on my ARM64 platform, with 1 GiB of memory the > > first [and only] section is allocated from the zeroing path while with > > 2 GiB of memory the first 1 GiB section is allocated from the > > non-zeroing path.) > > Do I get it right that sparse_buffer_init couldn't allocate memmap for > the full node for some reason and so sparse_init_nid would have to > allocate one for each memory section? Not quite. The sparsemap_buf is successfully allocated with the correct size in sparse_buffer_init(), but sparse_buffer_alloc() fails to allocate the same size from it. The reason it fails is that sparse_buffer_alloc() for some reason wants to return a pointer which is aligned to the allocation size. But the sparsemap_buf was only allocated with PAGE_SIZE alignment so there's not enough space to align it. I don't understand the reason for this alignment requirement since the fallback path also allocates with PAGE_SIZE alignment. I'm guessing the alignment is for the VMEMAP code which also uses sparse_buffer_alloc()?