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

[Corentin Labbe]

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.

Note that it never go down and when I terminate my X session, it stays the same.
So without any "real" GPU work, does it is still normal to have so many active mapping ?

For example, when doing some transfer, the ahci mapping number changes and then always go down to 6.