From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-wr0-f198.google.com (mail-wr0-f198.google.com [209.85.128.198]) by kanga.kvack.org (Postfix) with ESMTP id DC03C6B0007 for ; Tue, 17 Apr 2018 07:36:58 -0400 (EDT) Received: by mail-wr0-f198.google.com with SMTP id v11so16116799wri.13 for ; Tue, 17 Apr 2018 04:36:58 -0700 (PDT) Received: from mx2.suse.de (mx2.suse.de. [195.135.220.15]) by mx.google.com with ESMTPS id e17si1488695ede.310.2018.04.17.04.36.57 for (version=TLS1 cipher=AES128-SHA bits=128/128); Tue, 17 Apr 2018 04:36:57 -0700 (PDT) Date: Tue, 17 Apr 2018 13:36:56 +0200 From: Michal Hocko Subject: Re: [LSF/MM TOPIC] CMA and larger page sizes Message-ID: <20180417113656.GA16083@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 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? -- Michal Hocko SUSE Labs