From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-pg0-f70.google.com (mail-pg0-f70.google.com [74.125.83.70]) by kanga.kvack.org (Postfix) with ESMTP id 7DE256B0009 for ; Sat, 28 Apr 2018 04:33:06 -0400 (EDT) Received: by mail-pg0-f70.google.com with SMTP id m13-v6so3221629pgp.5 for ; Sat, 28 Apr 2018 01:33:06 -0700 (PDT) Received: from bombadil.infradead.org (bombadil.infradead.org. [2607:7c80:54:e::133]) by mx.google.com with ESMTPS id v12-v6si3227482plg.180.2018.04.28.01.33.05 for (version=TLS1_2 cipher=ECDHE-RSA-CHACHA20-POLY1305 bits=256/256); Sat, 28 Apr 2018 01:33:05 -0700 (PDT) Date: Sat, 28 Apr 2018 01:33:03 -0700 From: Christoph Hellwig Subject: Re: [LSF/MM TOPIC NOTES] x86 ZONE_DMA love Message-ID: <20180428083303.GB31684@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: Sender: owner-linux-mm@kvack.org List-ID: To: Christopher Lameter Cc: Michal Hocko , Christoph Hellwig , "Luis R. Rodriguez" , linux-mm@kvack.org, 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" On Fri, Apr 27, 2018 at 11:07:07AM -0500, Christopher Lameter wrote: > Well it looks like what we are using it for is to force allocation from > low physical memory if we fail to obtain proper memory through a normal > channel. The use of ZONE_DMA is only there for emergency purposes. > I think we could subsitute ZONE_DMA32 on x87 without a problem. > > Which means that ZONE_DMA has no purpose anymore. > > Can we make ZONE_DMA on x86 refer to the low 32 bit physical addresses > instead and remove ZONE_DMA32? While < 32-bit allocations are much more common there are plenty of requirements for < 24-bit or other weird masks still.