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From: Sergey Senozhatsky <senozhatsky@chromium.org>
To: Sergey Senozhatsky <senozhatsky@chromium.org>,
	Matthew Auld <matthew.william.auld@gmail.com>,
	Jani Nikula <jani.nikula@linux.intel.com>,
	Joonas Lahtinen <joonas.lahtinen@linux.intel.com>,
	David Airlie <airlied@linux.ie>,
	Chris Wilson <chris@chris-wilson.co.uk>,
	intel-gfx@lists.freedesktop.org, dri-devel@lists.freedesktop.org,
	linux-kernel@vger.kernel.org
Subject: Re: [Intel-gfx] drm/i915: __GFP_RETRY_MAYFAIL allocations in stable kernels
Date: Fri, 18 Jun 2021 11:29:30 +0900	[thread overview]
Message-ID: <YMwFCoHzjnuH80p6@google.com> (raw)
In-Reply-To: <YMuGGqs4cDotxuKO@phenom.ffwll.local>

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@chris-wilson.co.uk>
> 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.
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WARNING: multiple messages have this Message-ID (diff)
From: Sergey Senozhatsky <senozhatsky@chromium.org>
To: Sergey Senozhatsky <senozhatsky@chromium.org>,
	Matthew Auld <matthew.william.auld@gmail.com>,
	Jani Nikula <jani.nikula@linux.intel.com>,
	Joonas Lahtinen <joonas.lahtinen@linux.intel.com>,
	David Airlie <airlied@linux.ie>,
	Chris Wilson <chris@chris-wilson.co.uk>,
	intel-gfx@lists.freedesktop.org, dri-devel@lists.freedesktop.org,
	linux-kernel@vger.kernel.org
Subject: Re: drm/i915: __GFP_RETRY_MAYFAIL allocations in stable kernels
Date: Fri, 18 Jun 2021 11:29:30 +0900	[thread overview]
Message-ID: <YMwFCoHzjnuH80p6@google.com> (raw)
In-Reply-To: <YMuGGqs4cDotxuKO@phenom.ffwll.local>

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@chris-wilson.co.uk>
> 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.

  reply	other threads:[~2021-06-18  2:29 UTC|newest]

Thread overview: 15+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-06-14 12:45 [Intel-gfx] drm/i915: __GFP_RETRY_MAYFAIL allocations in stable kernels Sergey Senozhatsky
2021-06-14 12:45 ` Sergey Senozhatsky
2021-06-14 12:45 ` Sergey Senozhatsky
2021-06-14 23:38 ` [Intel-gfx] ✗ Fi.CI.BUILD: failure for " Patchwork
2021-06-17 17:27 ` [Intel-gfx] " Daniel Vetter
2021-06-17 17:27   ` Daniel Vetter
2021-06-17 17:27   ` Daniel Vetter
2021-06-18  2:29   ` Sergey Senozhatsky [this message]
2021-06-18  2:29     ` Sergey Senozhatsky
2021-06-18 15:46   ` [Intel-gfx] " Matthew Auld
2021-06-18 15:46     ` Matthew Auld
2021-06-18 15:46     ` Matthew Auld
2021-06-21 14:10     ` [Intel-gfx] " Daniel Vetter
2021-06-21 14:10       ` Daniel Vetter
2021-06-21 14:10       ` Daniel Vetter

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