Re: [PATCH 6/6] btrfs: check mergeable free space when removing acluster

[Josef Bacik]

On Mon, Aug 23, 2010 at 09:24:07AM +0800, Li Zefan wrote:
> After returing extents from a cluster to the block group, some
> extents in the block group may be mergeable.
> 
> Signed-off-by: Li Zefan <lizf@xxxxxxxxxxxxxx>
> ---
>  fs/btrfs/free-space-cache.c |   26 ++++++++++++++++++++------
>  1 files changed, 20 insertions(+), 6 deletions(-)
> 
> diff --git a/fs/btrfs/free-space-cache.c b/fs/btrfs/free-space-cache.c
> index faeec8f..c11f4f7 100644
> --- a/fs/btrfs/free-space-cache.c
> +++ b/fs/btrfs/free-space-cache.c
> @@ -234,11 +234,18 @@ tree_search_offset(struct btrfs_block_group_cache *block_group,
>  	return entry;
>  }
>  
> -static void unlink_free_space(struct btrfs_block_group_cache *block_group,
> -			      struct btrfs_free_space *info)
> +static inline void
> +__unlink_free_space(struct btrfs_block_group_cache *block_group,
> +		    struct btrfs_free_space *info)
>  {
>  	rb_erase(&info->offset_index, &block_group->free_space_offset);
>  	block_group->free_extents--;
> +}
> +
> +static void unlink_free_space(struct btrfs_block_group_cache *block_group,
> +			      struct btrfs_free_space *info)
> +{
> +	__unlink_free_space(block_group, info);
>  	block_group->free_space -= info->bytes;
>  }
>  
> @@ -611,7 +618,7 @@ out:
>  }
>  
>  bool try_merge_free_space(struct btrfs_block_group_cache *block_group,
> -			  struct btrfs_free_space *info)
> +			  struct btrfs_free_space *info, bool update_stat)
>  {
>  	struct btrfs_free_space *left_info;
>  	struct btrfs_free_space *right_info;
> @@ -632,7 +639,10 @@ bool try_merge_free_space(struct btrfs_block_group_cache *block_group,
>  		left_info = tree_search_offset(block_group, offset - 1, 0, 0);
>  
>  	if (right_info && !right_info->bitmap) {
> -		unlink_free_space(block_group, right_info);
> +		if (update_stat)
> +			unlink_free_space(block_group, right_info);
> +		else
> +			__unlink_free_space(block_group, right_info);
>  		info->bytes += right_info->bytes;
>  		kfree(right_info);
>  		merged = true;
> @@ -640,7 +650,10 @@ bool try_merge_free_space(struct btrfs_block_group_cache *block_group,
>  
>  	if (left_info && !left_info->bitmap &&
>  	    left_info->offset + left_info->bytes == offset) {
> -		unlink_free_space(block_group, left_info);
> +		if (update_stat)
> +			unlink_free_space(block_group, left_info);
> +		else
> +			__unlink_free_space(block_group, left_info);
>  		info->offset = left_info->offset;
>  		info->bytes += left_info->bytes;
>  		kfree(left_info);
> @@ -665,7 +678,7 @@ int btrfs_add_free_space(struct btrfs_block_group_cache *block_group,
>  
>  	spin_lock(&block_group->tree_lock);
>  
> -	if (try_merge_free_space(block_group, info))
> +	if (try_merge_free_space(block_group, info, true))
>  		goto link;
>  
>  	/*
> @@ -883,6 +896,7 @@ __btrfs_return_cluster_to_free_space(
>  		node = rb_next(&entry->offset_index);
>  		rb_erase(&entry->offset_index, &cluster->root);
>  		BUG_ON(entry->bitmap);
> +		try_merge_free_space(block_group, entry, false);
>  		tree_insert_offset(&block_group->free_space_offset,
>  				   entry->offset, &entry->offset_index, 0);

It's early in the morning here, so forgive me if I'm missing something obvious,
but if try_merge_free_space() succeeds here, then won't tree_insert_offset()
then add an entry that overlaps the same spot?  Should we do something like

merged = try_merge_free_space();
if (!merged)
	tree_insert_offset();

?  Thanks,

Josef
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