From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-pf0-f200.google.com (mail-pf0-f200.google.com [209.85.192.200]) by kanga.kvack.org (Postfix) with ESMTP id 0AF136B005A for ; Fri, 26 Jan 2018 22:51:46 -0500 (EST) Received: by mail-pf0-f200.google.com with SMTP id s22so1746787pfh.21 for ; Fri, 26 Jan 2018 19:51:46 -0800 (PST) Received: from mx2.suse.de (mx2.suse.de. [195.135.220.15]) by mx.google.com with ESMTPS id f63si7390057pfc.226.2018.01.26.19.51.44 for (version=TLS1 cipher=AES128-SHA bits=128/128); Fri, 26 Jan 2018 19:51:44 -0800 (PST) Date: Fri, 26 Jan 2018 18:25:27 +0100 From: Michal Hocko Subject: Re: [LSF/MM TOPIC] CMA and larger page sizes Message-ID: <20180126172527.GI5027@dhcp22.suse.cz> References: <3a3d724e-4d74-9bd8-60f3-f6896cffac7a@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <3a3d724e-4d74-9bd8-60f3-f6896cffac7a@redhat.com> Sender: owner-linux-mm@kvack.org List-ID: To: Laura Abbott Cc: lsf-pc@lists.linux-foundation.org, linux-mm@kvack.org, Joonsoo Kim [Ccing Joonsoo] 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 > > There's been some interest in other CMA topics so this might go along well. > > Thanks, > Laura > > -- > To unsubscribe, send a message with 'unsubscribe linux-mm' in > the body to majordomo@kvack.org. For more info on Linux MM, > see: http://www.linux-mm.org/ . > Don't email: email@kvack.org -- Michal Hocko SUSE Labs -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org