From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-ot0-f197.google.com (mail-ot0-f197.google.com [74.125.82.197]) by kanga.kvack.org (Postfix) with ESMTP id 13FEA6B027B for ; Tue, 17 Apr 2018 11:02:01 -0400 (EDT) Received: by mail-ot0-f197.google.com with SMTP id o3-v6so3293471oti.8 for ; Tue, 17 Apr 2018 08:02:01 -0700 (PDT) Received: from mail-sor-f41.google.com (mail-sor-f41.google.com. [209.85.220.41]) by mx.google.com with SMTPS id f72-v6sor7015768otf.258.2018.04.17.08.01.57 for (Google Transport Security); Tue, 17 Apr 2018 08:01:57 -0700 (PDT) Subject: Re: [LSF/MM TOPIC] CMA and larger page sizes References: <3a3d724e-4d74-9bd8-60f3-f6896cffac7a@redhat.com> <20180417113656.GA16083@dhcp22.suse.cz> From: Laura Abbott Message-ID: Date: Tue, 17 Apr 2018 08:01:53 -0700 MIME-Version: 1.0 In-Reply-To: <20180417113656.GA16083@dhcp22.suse.cz> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org List-ID: To: Michal Hocko Cc: lsf-pc@lists.linux-foundation.org, linux-mm@kvack.org On 04/17/2018 04:36 AM, Michal Hocko wrote: > On Fri 26-01-18 02:08:14, Laura Abbott wrote: >> CMA as it's currently designed requires alignment to the pageblock size c.f. >> >> /* >> * Sanitise input arguments. >> * Pages both ends in CMA area could be merged into adjacent unmovable >> * migratetype page by page allocator's buddy algorithm. In the case, >> * you couldn't get a contiguous memory, which is not what we want. >> */ >> alignment = max(alignment, (phys_addr_t)PAGE_SIZE << >> max_t(unsigned long, MAX_ORDER - 1, pageblock_order)); >> >> >> On arm64 with 64K page size and transparent huge page, this gives an alignment >> of 512MB. This is quite restrictive and can eat up significant portions of >> memory on smaller memory targets. Adjusting the configuration options really >> isn't ideal for distributions that aim to have a single image which runs on >> all targets. >> >> Approaches I've thought about: >> - Making CMA alignment less restrictive (and dealing with the fallout from >> the comment above) >> - Command line option to force a reasonable alignment > > Laura, are you still interested discussing this or other CMA related > topic? > In light of Joonsoo's patches, I don't think we need a lot of time but I'd still like some chance to discuss. I think there was some other interest in CMA topics so it can be combined with those if they are happening as well. Thanks, Laura