Re: [PATCH v4] drm: Optimise for continuous memory allocation

[Christian König <christian.koenig@xxxxxxx>]

Am 29.11.22 um 11:56 schrieb xinhui pan:
> Currently drm-buddy does not have full knowledge of continuous memory.
>
> Lets consider scenario below.
> order 1:    L		    R
> order 0: LL	LR	RL	RR
> for order 1 allocation, it can offer L or R or LR+RL.
>
> For now, we only implement L or R case for continuous memory allocation.
> So this patch aims to implement the rest cases.
>
> Adding a new member leaf_link which links all leaf blocks in asceding
> order. Now we can find more than 2 sub-order blocks easier.
> Say, order 4 can be combined with corresponding order 4, 2+2, 1+2+1,
> 0+1+2+0, 0+2+1+0.

Well that description is a bit confusing and doesn't make to much sense 
to me.

When you have two adjacent free order 0 blocks then those should be 
automatically combined into an order 1. This is a fundamental property 
of the buddy allocator, otherwise the whole algorithm won't work.

When you have the case of a free order 1 block with two adjacent free 
order 0 blocks then we a fragmented address space. In this case the best 
approach is to fail the allocation and start to swap things out.

So what exactly is the goal here?

Regards,
Christian.

> Signed-off-by: xinhui pan <xinhui.pan@xxxxxxx>
> ---
> change from v3:
> reworked totally. adding leaf_link.
>
> change from v2:
> search continuous block in nearby root if needed
>
> change from v1:
> implement top-down continuous allocation
> ---
>   drivers/gpu/drm/drm_buddy.c | 108 +++++++++++++++++++++++++++++++++---
>   include/drm/drm_buddy.h     |   1 +
>   2 files changed, 102 insertions(+), 7 deletions(-)
>
> diff --git a/drivers/gpu/drm/drm_buddy.c b/drivers/gpu/drm/drm_buddy.c
> index 11bb59399471..8edafb99b02c 100644
> --- a/drivers/gpu/drm/drm_buddy.c
> +++ b/drivers/gpu/drm/drm_buddy.c
> @@ -80,6 +80,7 @@ int drm_buddy_init(struct drm_buddy *mm, u64 size, u64 chunk_size)
>   {
>   	unsigned int i;
>   	u64 offset;
> +	LIST_HEAD(leaf);
>   
>   	if (size < chunk_size)
>   		return -EINVAL;
> @@ -136,6 +137,7 @@ int drm_buddy_init(struct drm_buddy *mm, u64 size, u64 chunk_size)
>   			goto out_free_roots;
>   
>   		mark_free(mm, root);
> +		list_add_tail(&root->leaf_link, &leaf);
>   
>   		BUG_ON(i > mm->max_order);
>   		BUG_ON(drm_buddy_block_size(mm, root) < chunk_size);
> @@ -147,6 +149,7 @@ int drm_buddy_init(struct drm_buddy *mm, u64 size, u64 chunk_size)
>   		i++;
>   	} while (size);
>   
> +	list_del(&leaf);
>   	return 0;
>   
>   out_free_roots:
> @@ -205,6 +208,9 @@ static int split_block(struct drm_buddy *mm,
>   	mark_free(mm, block->left);
>   	mark_free(mm, block->right);
>   
> +	list_add(&block->right->leaf_link, &block->leaf_link);
> +	list_add(&block->left->leaf_link, &block->leaf_link);
> +	list_del(&block->leaf_link);
>   	mark_split(block);
>   
>   	return 0;
> @@ -256,6 +262,9 @@ static void __drm_buddy_free(struct drm_buddy *mm,
>   			break;
>   
>   		list_del(&buddy->link);
> +		list_add(&parent->leaf_link, &block->leaf_link);
> +		list_del(&buddy->leaf_link);
> +		list_del(&block->leaf_link);
>   
>   		drm_block_free(mm, block);
>   		drm_block_free(mm, buddy);
> @@ -386,6 +395,78 @@ alloc_range_bias(struct drm_buddy *mm,
>   	return ERR_PTR(err);
>   }
>   
> +static struct drm_buddy_block *
> +find_continuous_blocks(struct drm_buddy *mm,
> +		       int order,
> +		       unsigned long flags,
> +		       struct drm_buddy_block **rblock)
> +{
> +	struct list_head *head = &mm->free_list[order];
> +	struct drm_buddy_block *free_block, *max_block = NULL, *end, *begin;
> +	u64 pages = BIT(order + 1);
> +	u64 cur_pages;
> +
> +	list_for_each_entry(free_block, head, link) {
> +		if (max_block) {
> +			if (!(flags & DRM_BUDDY_TOPDOWN_ALLOCATION))
> +				break;
> +
> +			if (drm_buddy_block_offset(free_block) <
> +			    drm_buddy_block_offset(max_block))
> +				continue;
> +		}
> +
> +		cur_pages = BIT(order);
> +		begin = end = free_block;
> +		while (true) {
> +			struct drm_buddy_block *prev, *next;
> +			int prev_order, next_order;
> +
> +			prev = list_prev_entry(begin, leaf_link);
> +			if (!drm_buddy_block_is_free(prev) ||
> +			    drm_buddy_block_offset(prev) >
> +			    drm_buddy_block_offset(begin)) {
> +				prev = NULL;
> +			}
> +			next = list_next_entry(end, leaf_link);
> +			if (!drm_buddy_block_is_free(next) ||
> +			    drm_buddy_block_offset(next) <
> +			    drm_buddy_block_offset(end)) {
> +				next = NULL;
> +			}
> +			if (!prev && !next)
> +				break;
> +
> +			prev_order = prev ? drm_buddy_block_order(prev) : -1;
> +			next_order = next ? drm_buddy_block_order(next) : -1;
> +			if (next_order >= prev_order) {
> +				BUG_ON(drm_buddy_block_offset(end) +
> +				       drm_buddy_block_size(mm, end) !=
> +				       drm_buddy_block_offset(next));
> +				end = next;
> +				cur_pages += BIT(drm_buddy_block_order(next));
> +			}
> +			if (prev_order >= next_order) {
> +				BUG_ON(drm_buddy_block_offset(prev) +
> +				       drm_buddy_block_size(mm, prev) !=
> +				       drm_buddy_block_offset(begin));
> +				begin = prev;
> +				cur_pages += BIT(drm_buddy_block_order(prev));
> +			}
> +			if (pages == cur_pages)
> +				break;
> +			BUG_ON(pages < cur_pages);
> +		}
> +
> +		if (pages > cur_pages)
> +			continue;
> +
> +		*rblock = end;
> +		max_block = begin;
> +	}
> +	return max_block;
> +}
> +
>   static struct drm_buddy_block *
>   get_maxblock(struct list_head *head)
>   {
> @@ -637,7 +718,7 @@ int drm_buddy_alloc_blocks(struct drm_buddy *mm,
>   			   struct list_head *blocks,
>   			   unsigned long flags)
>   {
> -	struct drm_buddy_block *block = NULL;
> +	struct drm_buddy_block *block = NULL, *rblock = NULL;
>   	unsigned int min_order, order;
>   	unsigned long pages;
>   	LIST_HEAD(allocated);
> @@ -689,17 +770,30 @@ int drm_buddy_alloc_blocks(struct drm_buddy *mm,
>   				break;
>   
>   			if (order-- == min_order) {
> +				if (!(flags & DRM_BUDDY_RANGE_ALLOCATION) &&
> +				    min_order != 0 && pages == BIT(order + 1)) {
> +					block = find_continuous_blocks(mm,
> +								       order,
> +								       flags,
> +								       &rblock);
> +					if (block)
> +						break;
> +				}
>   				err = -ENOSPC;
>   				goto err_free;
>   			}
>   		} while (1);
>   
> -		mark_allocated(block);
> -		mm->avail -= drm_buddy_block_size(mm, block);
> -		kmemleak_update_trace(block);
> -		list_add_tail(&block->link, &allocated);
> -
> -		pages -= BIT(order);
> +		do {
> +			mark_allocated(block);
> +			mm->avail -= drm_buddy_block_size(mm, block);
> +			kmemleak_update_trace(block);
> +			list_add_tail(&block->link, &allocated);
> +			pages -= BIT(drm_buddy_block_order(block));
> +			if (block == rblock || !rblock)
> +				break;
> +			block = list_next_entry(block, leaf_link);
> +		} while (true);
>   
>   		if (!pages)
>   			break;
> diff --git a/include/drm/drm_buddy.h b/include/drm/drm_buddy.h
> index 572077ff8ae7..c5437bd4f4f3 100644
> --- a/include/drm/drm_buddy.h
> +++ b/include/drm/drm_buddy.h
> @@ -50,6 +50,7 @@ struct drm_buddy_block {
>   	 */
>   	struct list_head link;
>   	struct list_head tmp_link;
> +	struct list_head leaf_link;
>   };
>   
>   /* Order-zero must be at least PAGE_SIZE */