On (21/06/17 19:27), Daniel Vetter wrote:
> >
> > So can all allocations in gen8_init_scratch() use
> > GFP_KERNEL | __GFP_RETRY_MAYFAIL | __GFP_NOWARN
>
> Yeah that looks all fairly broken tbh. The only thing I didn't know was
> that GFP_DMA32 wasn't a full gfp mask with reclaim bits set as needed. I
> guess it would be clearer if we use GFP_KERNEL | __GFP_DMA32 for these.
Looks good.
> The commit that introduced a lot of this, including I915_GFP_ALLOW_FAIL
> seems to be
>
> commit 1abb70f5955d1a9021f96359a2c6502ca569b68d
> Author: Chris Wilson <chris@xxxxxxxxxxxxxxxxxx>
> Date: Tue May 22 09:36:43 2018 +0100
>
> drm/i915/gtt: Allow pagedirectory allocations to fail
>
> which used a selftest as justification, not real world workloads, so looks
> rather dubious.
Exactly, the commit we landed internally partially reverts 1abb70f5955
in 4.19 and 5.4 kernels. I don't mind I915_GFP_ALLOW_FAIL and so on, I
kept those bits, but we need reclaim. I can reproduce cases when order:0
allocation fails with
__GFP_HIGHMEM|__GFP_RETRY_MAYFAIL
but succeeds with
GFP_KERNEL|__GFP_HIGHMEM|__GFP_RETRY_MAYFAIL
ON a side note, I'm not very sure if __GFP_RETRY_MAYFAIL is actually
needed. Especially seeing it in syscalls is a bit uncommon:
drm_ioctl()
i915_gem_context_create_ioctl()
i915_gem_create_context()
i915_ppgtt_create()
setup_scratch_page() // __GFP_RETRY_MAYFAIL
But with GFP_KERNEL at least it tries to make some reclaim progress
between retries, so it seems to be good enough.
