linux-kernel - Re: [PATCH 01/13] amdgpu: remove -EAGAIN handling for hmm_range

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Date:   Wed, 31 Jul 2019 13:13:41 +0000
From:   "Kuehling, Felix" <Felix.Kuehling@....com>
To:     Christoph Hellwig <hch@....de>,
        Jérôme Glisse <jglisse@...hat.com>,
        Jason Gunthorpe <jgg@...lanox.com>,
        Ben Skeggs <bskeggs@...hat.com>
CC:     Ralph Campbell <rcampbell@...dia.com>,
        "linux-mm@...ck.org" <linux-mm@...ck.org>,
        "nouveau@...ts.freedesktop.org" <nouveau@...ts.freedesktop.org>,
        "dri-devel@...ts.freedesktop.org" <dri-devel@...ts.freedesktop.org>,
        "amd-gfx@...ts.freedesktop.org" <amd-gfx@...ts.freedesktop.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 01/13] amdgpu: remove -EAGAIN handling for hmm_range_fault

On 2019-07-30 1:51 a.m., Christoph Hellwig wrote:
> hmm_range_fault can only return -EAGAIN if called with the block
> argument set to false, so remove the special handling for it.

The block argument no longer exists. You replaced that with the 
HMM_FAULT_ALLOW_RETRY with opposite logic. So this should read 
"hmm_range_fault can only return -EAGAIN if called with the 
HMM_FAULT_ALLOW_RETRY flag set, so remove the special handling for it.

With that fixed, this commit is Reviewed-by: Felix Kuehling 
<Felix.Kuehling@....com>

>
> Signed-off-by: Christoph Hellwig <hch@....de>
> ---
>   drivers/gpu/drm/amd/amdgpu/amdgpu_ttm.c | 23 +++--------------------
>   1 file changed, 3 insertions(+), 20 deletions(-)
>
> diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_ttm.c b/drivers/gpu/drm/amd/amdgpu/amdgpu_ttm.c
> index 12a59ac83f72..f0821638bbc6 100644
> --- a/drivers/gpu/drm/amd/amdgpu/amdgpu_ttm.c
> +++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_ttm.c
> @@ -778,7 +778,6 @@ int amdgpu_ttm_tt_get_user_pages(struct amdgpu_bo *bo, struct page **pages)
>   	struct hmm_range *range;
>   	unsigned long i;
>   	uint64_t *pfns;
> -	int retry = 0;
>   	int r = 0;
>   
>   	if (!mm) /* Happens during process shutdown */
> @@ -822,7 +821,6 @@ int amdgpu_ttm_tt_get_user_pages(struct amdgpu_bo *bo, struct page **pages)
>   	hmm_range_register(range, mirror, start,
>   			   start + ttm->num_pages * PAGE_SIZE, PAGE_SHIFT);
>   
> -retry:
>   	/*
>   	 * Just wait for range to be valid, safe to ignore return value as we
>   	 * will use the return value of hmm_range_fault() below under the
> @@ -831,24 +829,12 @@ int amdgpu_ttm_tt_get_user_pages(struct amdgpu_bo *bo, struct page **pages)
>   	hmm_range_wait_until_valid(range, HMM_RANGE_DEFAULT_TIMEOUT);
>   
>   	down_read(&mm->mmap_sem);
> -
>   	r = hmm_range_fault(range, 0);
> -	if (unlikely(r < 0)) {
> -		if (likely(r == -EAGAIN)) {
> -			/*
> -			 * return -EAGAIN, mmap_sem is dropped
> -			 */
> -			if (retry++ < MAX_RETRY_HMM_RANGE_FAULT)
> -				goto retry;
> -			else
> -				pr_err("Retry hmm fault too many times\n");
> -		}
> -
> -		goto out_up_read;
> -	}
> -
>   	up_read(&mm->mmap_sem);
>   
> +	if (unlikely(r < 0))
> +		goto out_free_pfns;
> +
>   	for (i = 0; i < ttm->num_pages; i++) {
>   		pages[i] = hmm_device_entry_to_page(range, pfns[i]);
>   		if (unlikely(!pages[i])) {
> @@ -864,9 +850,6 @@ int amdgpu_ttm_tt_get_user_pages(struct amdgpu_bo *bo, struct page **pages)
>   
>   	return 0;
>   
> -out_up_read:
> -	if (likely(r != -EAGAIN))
> -		up_read(&mm->mmap_sem);
>   out_free_pfns:
>   	hmm_range_unregister(range);
>   	kvfree(pfns);