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Date: Sat, 26 Sep 2020 16:14:28 +0200 From: Christoph Hellwig <hch@....de> To: Tomasz Figa <tfiga@...omium.org> Cc: Christoph Hellwig <hch@....de>, Mauro Carvalho Chehab <mchehab@...nel.org>, Thomas Bogendoerfer <tsbogend@...ha.franken.de>, "James E.J. Bottomley" <James.Bottomley@...senPartnership.com>, Joonyoung Shim <jy0922.shim@...sung.com>, Seung-Woo Kim <sw0312.kim@...sung.com>, Ben Skeggs <bskeggs@...hat.com>, Marek Szyprowski <m.szyprowski@...sung.com>, Matt Porter <mporter@...nel.crashing.org>, iommu@...ts.linux-foundation.org, Stefan Richter <stefanr@...6.in-berlin.de>, linux1394-devel@...ts.sourceforge.net, linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org, linux-media@...r.kernel.org, linux-arm-kernel@...ts.infradead.org, linux-mips@...r.kernel.org, linux-parisc@...r.kernel.org, linux-samsung-soc@...r.kernel.org, nouveau@...ts.freedesktop.org, netdev@...r.kernel.org, linux-scsi@...r.kernel.org, linux-mm@...ck.org, alsa-devel@...a-project.org Subject: Re: [PATCH 17/18] dma-iommu: implement ->alloc_noncoherent On Fri, Sep 25, 2020 at 06:46:22PM +0000, Tomasz Figa wrote: > > +static void *iommu_dma_alloc_noncoherent(struct device *dev, size_t size, > > + dma_addr_t *handle, enum dma_data_direction dir, gfp_t gfp) > > +{ > > + if (!gfpflags_allow_blocking(gfp)) { > > + struct page *page; > > + > > + page = dma_common_alloc_pages(dev, size, handle, dir, gfp); > > + if (!page) > > + return NULL; > > + return page_address(page); > > + } > > + > > + return iommu_dma_alloc_remap(dev, size, handle, gfp | __GFP_ZERO, > > + PAGE_KERNEL, 0); > > iommu_dma_alloc_remap() makes use of the DMA_ATTR_ALLOC_SINGLE_PAGES attribute > to optimize the allocations for devices which don't care about how contiguous > the backing memory is. Do you think we could add an attrs argument to this > function and pass it there? > > As ARM is being moved to the common iommu-dma layer as well, we'll probably > make use of the argument to support the DMA_ATTR_NO_KERNEL_MAPPING attribute to > conserve the vmalloc area. We could probably at it. However I wonder why this is something the drivers should care about. Isn't this really something that should be a kernel-wide policy for a given system?
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