From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1759698AbeD1IbC (ORCPT ); Sat, 28 Apr 2018 04:31:02 -0400 Received: from bombadil.infradead.org ([198.137.202.133]:42890 "EHLO bombadil.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1759584AbeD1IbA (ORCPT ); Sat, 28 Apr 2018 04:31:00 -0400 Date: Sat, 28 Apr 2018 01:30:49 -0700 From: Christoph Hellwig To: Michal Hocko Cc: Christoph Hellwig , "Luis R. Rodriguez" , linux-mm@kvack.org, cl@linux.com, Jan Kara , matthew@wil.cx, x86@kernel.org, luto@amacapital.net, martin.petersen@oracle.com, jthumshirn@suse.de, broonie@kernel.org, linux-spi@vger.kernel.org, linux-scsi@vger.kernel.org, linux-kernel@vger.kernel.org, "lsf-pc@lists.linux-foundation.org" Subject: Re: [LSF/MM TOPIC NOTES] x86 ZONE_DMA love Message-ID: <20180428083049.GA31684@infradead.org> References: <20180426215406.GB27853@wotan.suse.de> <20180427053556.GB11339@infradead.org> <20180427071843.GB17484@dhcp22.suse.cz> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20180427071843.GB17484@dhcp22.suse.cz> User-Agent: Mutt/1.9.2 (2017-12-15) X-SRS-Rewrite: SMTP reverse-path rewritten from by bombadil.infradead.org. See http://www.infradead.org/rpr.html Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, Apr 27, 2018 at 09:18:43AM +0200, Michal Hocko wrote: > > On Thu, Apr 26, 2018 at 09:54:06PM +0000, Luis R. Rodriguez wrote: > > > In practice if you don't have a floppy device on x86, you don't need ZONE_DMA, > > > > I call BS on that, and you actually explain later why it it BS due > > to some drivers using it more explicitly. But even more importantly > > we have plenty driver using it through dma_alloc_* and a small DMA > > mask, and they are in use - we actually had a 4.16 regression due to > > them. > > Well, but do we need a zone for that purpose? The idea was to actually > replace the zone by a CMA pool (at least on x86). With the current > implementation of the CMA we would move the range [0-16M] pfn range into > zone_movable so it can be used and we would get rid of all of the > overhead each zone brings (a bit in page flags, kmalloc caches and who > knows what else) That wasn't clear in the mail. But if we have anothr way to allocate <16MB memory we don't need ZONE_DMA for the floppy driver either, so the above conclusion is still wrong. > -- > Michal Hocko > SUSE Labs ---end quoted text---