On 04/12/2011 08:30 AM, Josef Bacik wrote:
> 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: Josef Bacik <josef@xxxxxxxxxx>
> ---
> fs/btrfs/ctree.h | 5 +++--
> fs/btrfs/extent-tree.c | 24 ++++++++++++++++++++++--
> 2 files changed, 25 insertions(+), 4 deletions(-)
>
> diff --git a/fs/btrfs/ctree.h b/fs/btrfs/ctree.h
> index 0d00a07..a566780 100644
> --- a/fs/btrfs/ctree.h
> +++ b/fs/btrfs/ctree.h
> @@ -740,10 +740,11 @@ 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 force_alloc; /* set if we need to force a chunk alloc for
> + int force_alloc:1; /* set if we need to force a chunk alloc for
> this space */
> + int chunk_alloc:1; /* set if we are allocating a chunk */
>
> struct list_head list;
>
> diff --git a/fs/btrfs/extent-tree.c b/fs/btrfs/extent-tree.c
> index f619c3c..80c048f 100644
> --- a/fs/btrfs/extent-tree.c
> +++ b/fs/btrfs/extent-tree.c
> @@ -3020,6 +3020,7 @@ static int update_space_info(struct btrfs_fs_info *info, u64 flags,
> found->bytes_may_use = 0;
> found->full = 0;
> found->force_alloc = 0;
> + found->chunk_alloc = 0;
> *space_info = found;
> list_add_rcu(&found->list, &info->space_info);
> atomic_set(&found->caching_threads, 0);
> @@ -3273,10 +3274,9 @@ 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);
> @@ -3287,6 +3287,7 @@ 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 = 1;
> @@ -3299,9 +3300,27 @@ static int do_chunk_alloc(struct btrfs_trans_handle *trans,
> alloc_bytes)) {
> spin_unlock(&space_info->lock);
> goto out;
hmm, the "goto" will lead to problems, cause in "out" clause there is a mutex_unlock(), which
we do not have a mutex_lock yet.
thanks,
liubo
> + } 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.
> @@ -3327,6 +3346,7 @@ static int do_chunk_alloc(struct btrfs_trans_handle *trans,
> space_info->full = 1;
> else
> ret = 1;
> + space_info->chunk_alloc = 0;
> space_info->force_alloc = 0;
> spin_unlock(&space_info->lock);
> out:
--
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