Re: [PATCH v4 09/11] xfs: refactor near mode alloc bnobt scan into separate function

["Darrick J. Wong" <darrick.wong@oracle.com>]

On Mon, Sep 16, 2019 at 08:16:33AM -0400, Brian Foster wrote:
> In preparation to enhance the near mode allocation bnobt scan algorithm, lift
> it into a separate function. No functional changes.
> 
> Signed-off-by: Brian Foster <bfoster@redhat.com>

Looks ok,
Reviewed-by: Darrick J. Wong <darrick.wong@oracle.com>

--D

> ---
>  fs/xfs/libxfs/xfs_alloc.c | 128 ++++++++++++++++++++++----------------
>  1 file changed, 74 insertions(+), 54 deletions(-)
> 
> diff --git a/fs/xfs/libxfs/xfs_alloc.c b/fs/xfs/libxfs/xfs_alloc.c
> index ab494fd50dd7..6f7e4666250c 100644
> --- a/fs/xfs/libxfs/xfs_alloc.c
> +++ b/fs/xfs/libxfs/xfs_alloc.c
> @@ -1223,6 +1223,78 @@ xfs_alloc_walk_iter(
>  	return 0;
>  }
>  
> +/*
> + * Search in the by-bno btree to the left and to the right simultaneously until
> + * in each case we find a large enough free extent or run into the edge of the
> + * tree. When we run into the edge of the tree, we deactivate that cursor.
> + */
> +STATIC int
> +xfs_alloc_ag_vextent_bnobt(
> +	struct xfs_alloc_arg	*args,
> +	struct xfs_alloc_cur	*acur,
> +	int			*stat)
> +{
> +	struct xfs_btree_cur	*fbcur = NULL;
> +	int			error;
> +	int			i;
> +	bool			fbinc;
> +
> +	ASSERT(acur->len == 0);
> +	ASSERT(args->type == XFS_ALLOCTYPE_NEAR_BNO);
> +
> +	*stat = 0;
> +
> +	error = xfs_alloc_lookup_le(acur->bnolt, args->agbno, 0, &i);
> +	if (error)
> +		return error;
> +	error = xfs_alloc_lookup_ge(acur->bnogt, args->agbno, 0, &i);
> +	if (error)
> +		return error;
> +
> +	/*
> +	 * Loop going left with the leftward cursor, right with the rightward
> +	 * cursor, until either both directions give up or we find an entry at
> +	 * least as big as minlen.
> +	 */
> +	while (xfs_alloc_cur_active(acur->bnolt) ||
> +	       xfs_alloc_cur_active(acur->bnogt)) {
> +		error = xfs_alloc_walk_iter(args, acur, acur->bnolt, false,
> +					    true, 1, &i);
> +		if (error)
> +			return error;
> +		if (i == 1) {
> +			trace_xfs_alloc_cur_left(args);
> +			fbcur = acur->bnogt;
> +			fbinc = true;
> +			break;
> +		}
> +
> +		error = xfs_alloc_walk_iter(args, acur, acur->bnogt, true, true,
> +					    1, &i);
> +		if (error)
> +			return error;
> +		if (i == 1) {
> +			trace_xfs_alloc_cur_right(args);
> +			fbcur = acur->bnolt;
> +			fbinc = false;
> +			break;
> +		}
> +	}
> +
> +	/* search the opposite direction for a better entry */
> +	if (fbcur) {
> +		error = xfs_alloc_walk_iter(args, acur, fbcur, fbinc, true, -1,
> +					    &i);
> +		if (error)
> +			return error;
> +	}
> +
> +	if (acur->len)
> +		*stat = 1;
> +
> +	return 0;
> +}
> +
>  /*
>   * Allocate a variable extent near bno in the allocation group agno.
>   * Extent's length (returned in len) will be between minlen and maxlen,
> @@ -1234,12 +1306,10 @@ xfs_alloc_ag_vextent_near(
>  	struct xfs_alloc_arg	*args)
>  {
>  	struct xfs_alloc_cur	acur = {0,};
> -	struct xfs_btree_cur	*fbcur = NULL;
>  	int		error;		/* error code */
>  	int		i;		/* result code, temporary */
>  	xfs_agblock_t	bno;
>  	xfs_extlen_t	len;
> -	bool		fbinc = false;
>  #ifdef DEBUG
>  	/*
>  	 * Randomly don't execute the first algorithm.
> @@ -1341,62 +1411,12 @@ xfs_alloc_ag_vextent_near(
>  	}
>  
>  	/*
> -	 * Second algorithm.
> -	 * Search in the by-bno tree to the left and to the right
> -	 * simultaneously, until in each case we find a space big enough,
> -	 * or run into the edge of the tree.  When we run into the edge,
> -	 * we deallocate that cursor.
> -	 * If both searches succeed, we compare the two spaces and pick
> -	 * the better one.
> -	 * With alignment, it's possible for both to fail; the upper
> -	 * level algorithm that picks allocation groups for allocations
> -	 * is not supposed to do this.
> +	 * Second algorithm. Search the bnobt left and right.
>  	 */
> -	error = xfs_alloc_lookup_le(acur.bnolt, args->agbno, 0, &i);
> -	if (error)
> -		goto out;
> -	error = xfs_alloc_lookup_ge(acur.bnogt, args->agbno, 0, &i);
> +	error = xfs_alloc_ag_vextent_bnobt(args, &acur, &i);
>  	if (error)
>  		goto out;
>  
> -	/*
> -	 * Loop going left with the leftward cursor, right with the rightward
> -	 * cursor, until either both directions give up or we find an entry at
> -	 * least as big as minlen.
> -	 */
> -	do {
> -		error = xfs_alloc_walk_iter(args, &acur, acur.bnolt, false,
> -					    true, 1, &i);
> -		if (error)
> -			goto out;
> -		if (i == 1) {
> -			trace_xfs_alloc_cur_left(args);
> -			fbcur = acur.bnogt;
> -			fbinc = true;
> -			break;
> -		}
> -
> -		error = xfs_alloc_walk_iter(args, &acur, acur.bnogt, true, true,
> -					    1, &i);
> -		if (error)
> -			goto out;
> -		if (i == 1) {
> -			trace_xfs_alloc_cur_right(args);
> -			fbcur = acur.bnolt;
> -			fbinc = false;
> -			break;
> -		}
> -	} while (xfs_alloc_cur_active(acur.bnolt) ||
> -		 xfs_alloc_cur_active(acur.bnogt));
> -
> -	/* search the opposite direction for a better entry */
> -	if (fbcur) {
> -		error = xfs_alloc_walk_iter(args, &acur, fbcur, fbinc, true, -1,
> -					    &i);
> -		if (error)
> -			goto out;
> -	}
> -
>  	/*
>  	 * If we couldn't get anything, give up.
>  	 */
> -- 
> 2.20.1
>