linux-kernel - Re: [PATCH 6/7] dma-iommu: implement ->alloc

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Message-ID: <YDyVFi26RPz5RrJB@google.com>
Date:   Mon, 1 Mar 2021 16:17:42 +0900
From:   Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>
To:     Christoph Hellwig <hch@....de>
Cc:     Tomasz Figa <tfiga@...omium.org>,
        Mauro Carvalho Chehab <mchehab@...nel.org>,
        Marek Szyprowski <m.szyprowski@...sung.com>,
        Ricardo Ribalda <ribalda@...omium.org>,
        Sergey Senozhatsky <senozhatsky@...gle.com>,
        "open list:IOMMU DRIVERS" <iommu@...ts.linux-foundation.org>,
        Robin Murphy <robin.murphy@....com>,
        Linux Doc Mailing List <linux-doc@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Linux Media Mailing List <linux-media@...r.kernel.org>
Subject: Re: [PATCH 6/7] dma-iommu: implement ->alloc_noncontiguous

On (21/02/16 09:49), Christoph Hellwig wrote:
> > When working on the videobuf2 integration with Sergey I noticed that
> > we always pass 0 as DMA attrs here, which removes the ability for
> > drivers to use DMA_ATTR_ALLOC_SINGLE_PAGES.
> > 
> > It's quite important from a system stability point of view, because by
> > default the iommu_dma allocator would prefer big order allocations for
> > TLB locality reasons. For many devices, though, it doesn't really
> > affect the performance, because of random access patterns, so single
> > pages are good enough and reduce the risk of allocation failures or
> > latency due to fragmentation.
> > 
> > Do you think we could add the attrs parameter to the
> > dma_alloc_noncontiguous() API?
> 
> Yes, we could probably do that.

I can cook a patch, unless somebody is already looking into it.

	-ss