From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-5.2 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 0113EC433E0 for ; Wed, 8 Jul 2020 16:10:17 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id C37E0206F6 for ; Wed, 8 Jul 2020 16:10:16 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1730490AbgGHQKP (ORCPT ); Wed, 8 Jul 2020 12:10:15 -0400 Received: from verein.lst.de ([213.95.11.211]:36073 "EHLO verein.lst.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1730282AbgGHQKO (ORCPT ); Wed, 8 Jul 2020 12:10:14 -0400 Received: by verein.lst.de (Postfix, from userid 2407) id 3407068B05; Wed, 8 Jul 2020 18:10:11 +0200 (CEST) Date: Wed, 8 Jul 2020 18:10:10 +0200 From: Christoph Hellwig To: Nicolas Saenz Julienne Cc: Christoph Hellwig , Marek Szyprowski , Robin Murphy , David Rientjes , linux-rpi-kernel@lists.infradead.org, jeremy.linton@arm.com, iommu@lists.linux-foundation.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH] dma-pool: use single atomic pool for both DMA zones Message-ID: <20200708161010.GA30184@lst.de> References: <20200707122804.21262-1-nsaenzjulienne@suse.de> <20200708153509.GA26743@lst.de> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.5.17 (2007-11-01) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Jul 08, 2020 at 06:00:35PM +0200, Nicolas Saenz Julienne wrote: > On Wed, 2020-07-08 at 17:35 +0200, Christoph Hellwig wrote: > > On Tue, Jul 07, 2020 at 02:28:04PM +0200, Nicolas Saenz Julienne wrote: > > > When allocating atomic DMA memory for a device, the dma-pool core > > > queries __dma_direct_optimal_gfp_mask() to check which atomic pool to > > > use. It turns out the GFP flag returned is only an optimistic guess. > > > The pool selected might sometimes live in a zone higher than the > > > device's view of memory. > > > > > > As there isn't a way to grantee a mapping between a device's DMA > > > constraints and correct GFP flags this unifies both DMA atomic pools. > > > The resulting pool is allocated in the lower DMA zone available, if any, > > > so as for devices to always get accessible memory while having the > > > flexibility of using dma_pool_kernel for the non constrained ones. > > > > > > Fixes: c84dc6e68a1d ("dma-pool: add additional coherent pools to map to gfp > > > mask") > > > Reported-by: Jeremy Linton > > > Suggested-by: Robin Murphy > > > Signed-off-by: Nicolas Saenz Julienne > > > > Hmm, this is not what I expected from the previous thread. I thought > > we'd just use one dma pool based on runtime available of the zones.. > > I may be misunderstanding you, but isn't that going back to how things used to > be before pulling in David Rientjes' work? The benefit of having a GFP_KERNEL > pool is that non-address-constrained devices can get their atomic memory there, > instead of consuming somewhat scarcer low memory. Yes, I think we are misunderstanding each other. I don't want to remove any pool, just make better runtime decisions when to use them.