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Subject: Re: DMA-API: cacheline tracking ENOMEM, dma-debug disabled due to
 nouveau ?
To:     Christoph Hellwig <hch@lst.de>,
        Corentin Labbe <clabbe.montjoie@gmail.com>, bskeggs@redhat.com,
        airlied@linux.ie, m.szyprowski@samsung.com,
        dri-devel@lists.freedesktop.org, nouveau@lists.freedesktop.org,
        linux-kernel@vger.kernel.org, iommu@lists.linux-foundation.org
References: <20190814145033.GA11190@Red>
 <20190814174927.GT7444@phenom.ffwll.local> <20190815133554.GE12036@lst.de>
From:   Robin Murphy <robin.murphy@arm.com>
Message-ID: <cdb43f4b-55ff-80c3-8d27-56238b2ab1a1@arm.com>
Date:   Thu, 15 Aug 2019 14:50:52 +0100
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On 15/08/2019 14:35, Christoph Hellwig wrote:
> On Wed, Aug 14, 2019 at 07:49:27PM +0200, Daniel Vetter wrote:
>> On Wed, Aug 14, 2019 at 04:50:33PM +0200, Corentin Labbe wrote:
>>> Hello
>>>
>>> Since lot of release (at least since 4.19), I hit the following error message:
>>> DMA-API: cacheline tracking ENOMEM, dma-debug disabled
>>>
>>> After hitting that, I try to check who is creating so many DMA mapping and see:
>>> cat /sys/kernel/debug/dma-api/dump | cut -d' ' -f2 | sort | uniq -c
>>>        6 ahci
>>>      257 e1000e
>>>        6 ehci-pci
>>>     5891 nouveau
>>>       24 uhci_hcd
>>>
>>> Does nouveau having this high number of DMA mapping is normal ?
>>
>> Yeah seems perfectly fine for a gpu.
> 
> That is a lot and apparently overwhelm the dma-debug tracking.  Robin
> rewrote this code in Linux 4.21 to work a little better, so I'm curious
> why this might have changes in 4.19, as dma-debug did not change at
> all there.

FWIW, the cacheline tracking entries are a separate thing from the 
dma-debug entries that I rejigged - judging by those numbers there 
should still be plenty of free dma-debug entries, but for some reason it 
has failed to extend the radix tree :/

Robin.