Re: [PATCH 07/36] btrfs: check if free bgs for commit

[Omar Sandoval <osandov@osandov.com>]

On Tue, Sep 11, 2018 at 01:57:38PM -0400, Josef Bacik wrote:
> may_commit_transaction will skip committing the transaction if we don't
> have enough pinned space or if we're trying to find space for a SYSTEM
> chunk.  However if we have pending free block groups in this transaction
> we still want to commit as we may be able to allocate a chunk to make
> our reservation.  So instead of just returning ENOSPC, check if we have
> free block groups pending, and if so commit the transaction to allow us
> to use that free space.

Reviewed-by: Omar Sandoval <osandov@fb.com>

> Signed-off-by: Josef Bacik <josef@toxicpanda.com>
> ---
>  fs/btrfs/extent-tree.c | 33 +++++++++++++++++++--------------
>  1 file changed, 19 insertions(+), 14 deletions(-)
> 
> diff --git a/fs/btrfs/extent-tree.c b/fs/btrfs/extent-tree.c
> index 7168e2476944..a3baa16d456f 100644
> --- a/fs/btrfs/extent-tree.c
> +++ b/fs/btrfs/extent-tree.c
> @@ -4830,10 +4830,18 @@ static int may_commit_transaction(struct btrfs_fs_info *fs_info,
>  	if (!bytes)
>  		return 0;
>  
> -	/* See if there is enough pinned space to make this reservation */
> -	if (__percpu_counter_compare(&space_info->total_bytes_pinned,
> -				   bytes,
> -				   BTRFS_TOTAL_BYTES_PINNED_BATCH) >= 0)
> +	trans = btrfs_join_transaction(fs_info->extent_root);
> +	if (IS_ERR(trans))
> +		return -ENOSPC;
> +
> +	/*
> +	 * See if there is enough pinned space to make this reservation, or if
> +	 * we have bg's that are going to be freed, allowing us to possibly do a
> +	 * chunk allocation the next loop through.
> +	 */
> +	if (test_bit(BTRFS_TRANS_HAVE_FREE_BGS, &trans->transaction->flags) ||
> +	    __percpu_counter_compare(&space_info->total_bytes_pinned, bytes,
> +				     BTRFS_TOTAL_BYTES_PINNED_BATCH) >= 0)
>  		goto commit;
>  
>  	/*
> @@ -4841,7 +4849,7 @@ static int may_commit_transaction(struct btrfs_fs_info *fs_info,
>  	 * this reservation.
>  	 */
>  	if (space_info != delayed_rsv->space_info)
> -		return -ENOSPC;
> +		goto enospc;
>  
>  	spin_lock(&delayed_rsv->lock);
>  	reclaim_bytes += delayed_rsv->reserved;
> @@ -4855,17 +4863,14 @@ static int may_commit_transaction(struct btrfs_fs_info *fs_info,
>  	bytes -= reclaim_bytes;
>  
>  	if (__percpu_counter_compare(&space_info->total_bytes_pinned,
> -				   bytes,
> -				   BTRFS_TOTAL_BYTES_PINNED_BATCH) < 0) {
> -		return -ENOSPC;
> -	}
> -
> +				     bytes,
> +				     BTRFS_TOTAL_BYTES_PINNED_BATCH) < 0)
> +		goto enospc;
>  commit:
> -	trans = btrfs_join_transaction(fs_info->extent_root);
> -	if (IS_ERR(trans))
> -		return -ENOSPC;
> -
>  	return btrfs_commit_transaction(trans);
> +enospc:
> +	btrfs_end_transaction(trans);
> +	return -ENOSPC;
>  }
>  
>  /*
> -- 
> 2.14.3
>