Re: [PATCH 7/7] drm/selftests: add drm buddy pathological testcase

[Matthew Auld <matthew.auld@intel.com>]

On 03/02/2022 13:32, Arunpravin wrote:
> create a pot-sized mm, then allocate one of each possible
> order within. This should leave the mm with exactly one
> page left. Free the largest block, then whittle down again.
> Eventually we will have a fully 50% fragmented mm.
> 
> Signed-off-by: Arunpravin <Arunpravin.PaneerSelvam@amd.com>
> ---
>   .../gpu/drm/selftests/drm_buddy_selftests.h   |   1 +
>   drivers/gpu/drm/selftests/test-drm_buddy.c    | 136 ++++++++++++++++++
>   2 files changed, 137 insertions(+)
> 
> diff --git a/drivers/gpu/drm/selftests/drm_buddy_selftests.h b/drivers/gpu/drm/selftests/drm_buddy_selftests.h
> index 411d072cbfc5..455b756c4ae5 100644
> --- a/drivers/gpu/drm/selftests/drm_buddy_selftests.h
> +++ b/drivers/gpu/drm/selftests/drm_buddy_selftests.h
> @@ -12,3 +12,4 @@ selftest(buddy_alloc_range, igt_buddy_alloc_range)
>   selftest(buddy_alloc_optimistic, igt_buddy_alloc_optimistic)
>   selftest(buddy_alloc_pessimistic, igt_buddy_alloc_pessimistic)
>   selftest(buddy_alloc_smoke, igt_buddy_alloc_smoke)
> +selftest(buddy_alloc_pathological, igt_buddy_alloc_pathological)
> diff --git a/drivers/gpu/drm/selftests/test-drm_buddy.c b/drivers/gpu/drm/selftests/test-drm_buddy.c
> index 2074e8c050a4..b2d0313a4bc5 100644
> --- a/drivers/gpu/drm/selftests/test-drm_buddy.c
> +++ b/drivers/gpu/drm/selftests/test-drm_buddy.c
> @@ -338,6 +338,142 @@ static void igt_mm_config(u64 *size, u64 *chunk_size)
>   	*size = (u64)s << 12;
>   }
>   
> +static int igt_buddy_alloc_pathological(void *arg)
> +{
> +	u64 mm_size, size, min_page_size, start = 0;
> +	struct drm_buddy_block *block;
> +	const int max_order = 3;
> +	unsigned long flags = 0;
> +	int order, top, err;
> +	struct drm_buddy mm;
> +	LIST_HEAD(blocks);
> +	LIST_HEAD(holes);
> +	LIST_HEAD(tmp);
> +
> +	/*
> +	 * Create a pot-sized mm, then allocate one of each possible
> +	 * order within. This should leave the mm with exactly one
> +	 * page left. Free the largest block, then whittle down again.
> +	 * Eventually we will have a fully 50% fragmented mm.
> +	 */
> +
> +	mm_size = PAGE_SIZE << max_order;
> +	err = drm_buddy_init(&mm, mm_size, PAGE_SIZE);
> +	if (err) {
> +		pr_err("buddy_init failed(%d)\n", err);
> +		return err;
> +	}
> +	BUG_ON(mm.max_order != max_order);
> +
> +	for (top = max_order; top; top--) {
> +		/* Make room by freeing the largest allocated block */
> +		block = list_first_entry_or_null(&blocks, typeof(*block), link);
> +		if (block) {
> +			list_del(&block->link);
> +			drm_buddy_free_block(&mm, block);
> +		}
> +
> +		for (order = top; order--; ) {
> +			size = min_page_size = get_size(order, PAGE_SIZE);
> +			err = drm_buddy_alloc_blocks(&mm, start, mm_size, size,
> +						     min_page_size, &tmp, flags);
> +			if (err) {
> +				pr_info("buddy_alloc hit -ENOMEM with order=%d, top=%d\n",
> +					order, top);
> +				goto err;
> +			}
> +
> +			block = list_first_entry_or_null(&tmp,
> +							 struct drm_buddy_block,
> +							 link);
> +			if (!block) {
> +				pr_err("alloc_blocks has no blocks\n");
> +				err = -EINVAL;
> +				goto err;
> +			}
> +
> +			list_del(&block->link);
> +			list_add_tail(&block->link, &blocks);
> +		}
> +
> +		/* There should be one final page for this sub-allocation */
> +		size = min_page_size = get_size(0, PAGE_SIZE);
> +		err = drm_buddy_alloc_blocks(&mm, start, mm_size, size, min_page_size, &tmp, flags);
> +		if (err) {
> +			pr_info("buddy_alloc hit -ENOME for hole\n");

ENOMEM

Reviewed-by: Matthew Auld <matthew.auld@intel.com>

> +			goto err;
> +		}
> +
> +		block = list_first_entry_or_null(&tmp,
> +						 struct drm_buddy_block,
> +						 link);
> +		if (!block) {
> +			pr_err("alloc_blocks has no blocks\n");
> +			err = -EINVAL;
> +			goto err;
> +		}
> +
> +		list_del(&block->link);
> +		list_add_tail(&block->link, &holes);
> +
> +		size = min_page_size = get_size(top, PAGE_SIZE);
> +		err = drm_buddy_alloc_blocks(&mm, start, mm_size, size, min_page_size, &tmp, flags);
> +		if (!err) {
> +			pr_info("buddy_alloc unexpectedly succeeded at top-order %d/%d, it should be full!",
> +				top, max_order);
> +			block = list_first_entry_or_null(&tmp,
> +							 struct drm_buddy_block,
> +							 link);
> +			if (!block) {
> +				pr_err("alloc_blocks has no blocks\n");
> +				err = -EINVAL;
> +				goto err;
> +			}
> +
> +			list_del(&block->link);
> +			list_add_tail(&block->link, &blocks);
> +			err = -EINVAL;
> +			goto err;
> +		}
> +	}
> +
> +	drm_buddy_free_list(&mm, &holes);
> +
> +	/* Nothing larger than blocks of chunk_size now available */
> +	for (order = 1; order <= max_order; order++) {
> +		size = min_page_size = get_size(order, PAGE_SIZE);
> +		err = drm_buddy_alloc_blocks(&mm, start, mm_size, size, min_page_size, &tmp, flags);
> +		if (!err) {
> +			pr_info("buddy_alloc unexpectedly succeeded at order %d, it should be full!",
> +				order);
> +			block = list_first_entry_or_null(&tmp,
> +							 struct drm_buddy_block,
> +							 link);
> +			if (!block) {
> +				pr_err("alloc_blocks has no blocks\n");
> +				err = -EINVAL;
> +				goto err;
> +			}
> +
> +			list_del(&block->link);
> +			list_add_tail(&block->link, &blocks);
> +			err = -EINVAL;
> +			goto err;
> +		}
> +	}
> +
> +	if (err) {
> +		pr_info("%s - succeeded\n", __func__);
> +		err = 0;
> +	}
> +
> +err:
> +	list_splice_tail(&holes, &blocks);
> +	drm_buddy_free_list(&mm, &blocks);
> +	drm_buddy_fini(&mm);
> +	return err;
> +}
> +
>   static int igt_buddy_alloc_smoke(void *arg)
>   {
>   	u64 mm_size, min_page_size, chunk_size, start = 0;