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=-2.2 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 CC0ACFA372A for ; Wed, 16 Oct 2019 15:31:13 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id A90B220854 for ; Wed, 16 Oct 2019 15:31:13 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2394160AbfJPPbM (ORCPT ); Wed, 16 Oct 2019 11:31:12 -0400 Received: from foss.arm.com ([217.140.110.172]:43402 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726332AbfJPPbM (ORCPT ); Wed, 16 Oct 2019 11:31:12 -0400 Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id AB43D142F; Wed, 16 Oct 2019 08:31:11 -0700 (PDT) Received: from [192.168.0.129] (unknown [172.31.20.19]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id AFE353F68E; Wed, 16 Oct 2019 08:31:07 -0700 (PDT) Subject: Re: [PATCH V2] mm/page_alloc: Add alloc_contig_pages() To: Michal Hocko , David Hildenbrand Cc: linux-mm@kvack.org, Mike Kravetz , Andrew Morton , Vlastimil Babka , David Rientjes , Andrea Arcangeli , Oscar Salvador , Mel Gorman , Mike Rapoport , Dan Williams , Pavel Tatashin , Matthew Wilcox , linux-kernel@vger.kernel.org References: <1571223765-10662-1-git-send-email-anshuman.khandual@arm.com> <40b8375c-5291-b477-1519-fd7fa799a67d@redhat.com> <20191016115119.GA317@dhcp22.suse.cz> <20191016124149.GB317@dhcp22.suse.cz> From: Anshuman Khandual Message-ID: <97cadd99-d05e-3174-6532-fe18f0301ba7@arm.com> Date: Wed, 16 Oct 2019 21:01:19 +0530 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.9.1 MIME-Version: 1.0 In-Reply-To: <20191016124149.GB317@dhcp22.suse.cz> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 10/16/2019 06:11 PM, Michal Hocko wrote: > On Wed 16-10-19 14:29:05, David Hildenbrand wrote: >> On 16.10.19 13:51, Michal Hocko wrote: >>> On Wed 16-10-19 16:43:57, Anshuman Khandual wrote: >>>> >>>> >>>> On 10/16/2019 04:39 PM, David Hildenbrand wrote: >>> [...] >>>>> Just to make sure, you ignored my comment regarding alignment >>>>> although I explicitly mentioned it a second time? Thanks. >>>> >>>> I had asked Michal explicitly what to be included for the respin. Anyways >>>> seems like the previous thread is active again. I am happy to incorporate >>>> anything new getting agreed on there. >>> >>> Your patch is using the same alignment as the original code would do. If >>> an explicit alignement is needed then this can be added on top, right? >>> >> >> Again, the "issue" I see here is that we could now pass in numbers that are >> not a power of two. For gigantic pages it was clear that we always have a >> number of two. The alignment does not make any sense otherwise. ALIGN() does expect nr_pages two be power of two otherwise the mask value might not be correct, affecting start pfn value for a zone. #define ALIGN(x, a) __ALIGN_KERNEL((x), (a)) #define __ALIGN_KERNEL(x, a) __ALIGN_KERNEL_MASK(x, (typeof(x))(a) - 1) #define __ALIGN_KERNEL_MASK(x, mask) (((x) + (mask)) & ~(mask)) >> >> What I'm asking for is >> >> a) Document "The resulting PFN is aligned to nr_pages" and "nr_pages should >> be a power of two". > > OK, this makes sense. Sure, will add this to the alloc_contig_pages() helper description and in the commit message as well. > >> b) Eventually adding something like >> >> if (WARN_ON_ONCE(!is_power_of_2(nr_pages))) >> return NULL; > > I am not sure this is really needed. > Just wondering why not ? Ideally if we are documenting that nr_pages should be power of two, then we should abort erring allocation request with an warning. Is it because allocation can still succeed for non-power-of-two requests despite possible problem with mask and alignment ? Hence there is no need to abort it.