Commit 6d74119f authored by Josef Bacik's avatar Josef Bacik Committed by Chris Mason
Browse files

Btrfs: avoid taking the chunk_mutex in do_chunk_alloc 



Everytime we try to allocate disk space we try and see if we can pre-emptively
allocate a chunk, but in the common case we don't allocate anything, so there is
no sense in taking the chunk_mutex at all.  So instead if we are allocating a
chunk, mark it in the space_info so we don't get two people trying to allocate
at the same time.  Thanks,

Signed-off-by: default avatarJosef Bacik <josef@redhat.com>
Reviewed-by: default avatarLiu Bo <liubo2009@cn.fujitsu.com>
parent 0d399205

fs/btrfs/ctree.h

+3 −1
Original line number Diff line number Diff line
@@ -740,8 +740,10 @@ struct btrfs_space_info { 
	 */

	unsigned long reservation_progress;



	int full;		/* indicates that we cannot allocate any more

	int full:1;		/* indicates that we cannot allocate any more

				   chunks for this space */

	int chunk_alloc:1;	/* set if we are allocating a chunk */



	int force_alloc;	/* set if we need to force a chunk alloc for

				   this space */

fs/btrfs/extent-tree.c

+25 −5
Original line number Diff line number Diff line
@@ -3039,6 +3039,7 @@ static int update_space_info(struct btrfs_fs_info *info, u64 flags, 
	found->bytes_may_use = 0;

	found->full = 0;

	found->force_alloc = CHUNK_ALLOC_NO_FORCE;

	found->chunk_alloc = 0;

	*space_info = found;

	list_add_rcu(&found->list, &info->space_info);

	atomic_set(&found->caching_threads, 0);
@@ -3318,10 +3319,9 @@ static int do_chunk_alloc(struct btrfs_trans_handle *trans, 
{

	struct btrfs_space_info *space_info;

	struct btrfs_fs_info *fs_info = extent_root->fs_info;

	int wait_for_alloc = 0;

	int ret = 0;



	mutex_lock(&fs_info->chunk_mutex);



	flags = btrfs_reduce_alloc_profile(extent_root, flags);



	space_info = __find_space_info(extent_root->fs_info, flags);
@@ -3332,21 +3332,40 @@ static int do_chunk_alloc(struct btrfs_trans_handle *trans, 
	}

	BUG_ON(!space_info);



again:

	spin_lock(&space_info->lock);

	if (space_info->force_alloc)

		force = space_info->force_alloc;

	if (space_info->full) {

		spin_unlock(&space_info->lock);

		goto out;

		return 0;

	}



	if (!should_alloc_chunk(extent_root, space_info, alloc_bytes, force)) {

		spin_unlock(&space_info->lock);

		goto out;

		return 0;

	} else if (space_info->chunk_alloc) {

		wait_for_alloc = 1;

	} else {

		space_info->chunk_alloc = 1;

	}



	spin_unlock(&space_info->lock);



	mutex_lock(&fs_info->chunk_mutex);



	/*

	 * The chunk_mutex is held throughout the entirety of a chunk

	 * allocation, so once we've acquired the chunk_mutex we know that the

	 * other guy is done and we need to recheck and see if we should

	 * allocate.

	 */

	if (wait_for_alloc) {

		mutex_unlock(&fs_info->chunk_mutex);

		wait_for_alloc = 0;

		goto again;

	}



	/*

	 * If we have mixed data/metadata chunks we want to make sure we keep

	 * allocating mixed chunks instead of individual chunks.
@@ -3372,9 +3391,10 @@ static int do_chunk_alloc(struct btrfs_trans_handle *trans, 
		space_info->full = 1;

	else

		ret = 1;



	space_info->force_alloc = CHUNK_ALLOC_NO_FORCE;

	space_info->chunk_alloc = 0;

	spin_unlock(&space_info->lock);

out:

	mutex_unlock(&extent_root->fs_info->chunk_mutex);

	return ret;

}

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