linux-kernel - Re: DMA-API: cacheline tracking ENOMEM, dma-debug disabled due to nouveau ?

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Date:   Thu, 15 Aug 2019 14:50:52 +0100
From:   Robin Murphy <robin.murphy@....com>
To:     Christoph Hellwig <hch@....de>,
        Corentin Labbe <clabbe.montjoie@...il.com>, bskeggs@...hat.com,
        airlied@...ux.ie, m.szyprowski@...sung.com,
        dri-devel@...ts.freedesktop.org, nouveau@...ts.freedesktop.org,
        linux-kernel@...r.kernel.org, iommu@...ts.linux-foundation.org
Subject: Re: DMA-API: cacheline tracking ENOMEM, dma-debug disabled due to
 nouveau ?

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.