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Thu, 09 Jul 2020 14:49:37 -0700 (PDT) Date: Thu, 9 Jul 2020 14:49:37 -0700 (PDT) X-X-Sender: rientjes@chino.kir.corp.google.com To: Christoph Hellwig Subject: Re: [PATCH] dma-pool: use single atomic pool for both DMA zones In-Reply-To: <20200708161010.GA30184@lst.de> Message-ID: References: <20200707122804.21262-1-nsaenzjulienne@suse.de> <20200708153509.GA26743@lst.de> <20200708161010.GA30184@lst.de> User-Agent: Alpine 2.23 (DEB 453 2020-06-18) MIME-Version: 1.0 Cc: linux-kernel@vger.kernel.org, jeremy.linton@arm.com, iommu@lists.linux-foundation.org, linux-rpi-kernel@lists.infradead.org, Robin Murphy X-BeenThere: iommu@lists.linux-foundation.org X-Mailman-Version: 2.1.15 Precedence: list List-Id: Development issues for Linux IOMMU support List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , From: David Rientjes via iommu Reply-To: David Rientjes Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Errors-To: iommu-bounces@lists.linux-foundation.org Sender: "iommu" On Wed, 8 Jul 2020, Christoph Hellwig wrote: > 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. > Just to be extra explicit for the record and for my own understanding: Nicolas, your patch series "dma-pool: Fix atomic pool selection" obsoletes this patch, right? :) _______________________________________________ iommu mailing list iommu@lists.linux-foundation.org https://lists.linuxfoundation.org/mailman/listinfo/iommu