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[216.228.112.22]) by smtp.gmail.com with ESMTPSA id u123sm10641854pfb.1.2019.02.06.18.28.52 (version=TLS1_2 cipher=ECDHE-RSA-CHACHA20-POLY1305 bits=256/256); Wed, 06 Feb 2019 18:28:53 -0800 (PST) Date: Wed, 6 Feb 2019 18:28:49 -0800 From: Nicolin Chen To: Christoph Hellwig Cc: m.szyprowski@samsung.com, robin.murphy@arm.com, vdumpa@nvidia.com, iommu@lists.linux-foundation.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH v2] dma-direct: do not allocate a single page from CMA area Message-ID: <20190207022848.GA5581@Asurada-Nvidia.nvidia.com> References: <20190115215140.1545-1-nicoleotsuka@gmail.com> <20190204082307.GA5916@lst.de> <20190205230514.GA21515@Asurada-Nvidia.nvidia.com> <20190206070726.GE23392@lst.de> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20190206070726.GE23392@lst.de> User-Agent: Mutt/1.9.4 (2018-02-28) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi Christoph, On Wed, Feb 06, 2019 at 08:07:26AM +0100, Christoph Hellwig wrote: > On Tue, Feb 05, 2019 at 03:05:30PM -0800, Nicolin Chen wrote: > > > And my other concern is that this skips allocating from the per-device > > > pool, which drivers might rely on. > > > > Actually Robin had the same concern at v1 and suggested that we could > > always use DMA_ATTR_FORCE_CONTIGUOUS to enforce into per-device pool. > > That is both against the documented behavior of DMA_ATTR_FORCE_CONTIGUOUS > and doesn't help existing drivers that specify their CMA area in DT. OK. I will drop it. > > > To be honest I'm not sure there is > > > much of a point in the per-device CMA pool vs the traditional per-device > > > coherent pool, but I'd rather change that behavior in a clearly documented > > > commit with intentions rather as a side effect from a random optimization. > > > > Hmm..sorry, I don't really follow this suggestion. Is it possible for > > you to make it clear that what should I do for the change? > > Something like this (plus proper comments): > > diff --git a/kernel/dma/contiguous.c b/kernel/dma/contiguous.c > index b2a87905846d..789d734f0f77 100644 > --- a/kernel/dma/contiguous.c > +++ b/kernel/dma/contiguous.c > @@ -192,10 +192,19 @@ int __init dma_contiguous_reserve_area(phys_addr_t size, phys_addr_t base, > struct page *dma_alloc_from_contiguous(struct device *dev, size_t count, > unsigned int align, bool no_warn) > { > + struct cma *cma; > + > if (align > CONFIG_CMA_ALIGNMENT) > align = CONFIG_CMA_ALIGNMENT; > > - return cma_alloc(dev_get_cma_area(dev), count, align, no_warn); > + if (dev && dev->cma_area) > + cma = dev->cma_area; > + else if (count > PAGE_SIZE) > + cma = dma_contiguous_default_area; > + else > + return NULL; So we will keep allocating single pages in dev->cma_area if it's present, in order to address your previous concern? Thanks Nicolin