Re: [PATCH v3 0/8] drm: Introduce sparse GEM shmem

[Boris Brezillon <boris.brezillon@collabora.com>]

On Fri, 11 Apr 2025 14:45:49 +0200
Christian König <christian.koenig@amd.com> wrote:

> Am 11.04.25 um 14:02 schrieb Boris Brezillon:
> >>> I guess this leaves older GPUs that don't support incremental
> >>> rendering in a bad place though.    
> >> Well what's the handling there currently? Just crash when you're
> >> OOM?  
> > It's "alloc(GFP_KERNEL) and crash if it fails or times out", yes.  
> 
> Oh, please absolutely don't! Using GFP_KERNEL here is as evil as it
> can be.

I'm not saying that's what we should do, I'm just telling you what's
done at the moment. The whole point of this series is to address some
that mess :P.

> 
> Background is that you don't get a crash, nor error message, nor
> anything indicating what is happening.

The job times out at some point, but we might get stuck in the fault
handler waiting for memory, which is pretty close to a deadlock, I
suspect.

> 
> You just get a deadlocked system with the user wondering why the heck
> the system doesn't response any more.

Not sure that's a true deadlock, for the reason explained before (no
shrinker in panthor, and panfrost only reclaims idle BOs, so no waits
on fences there either), but that doesn't make things great either.