Re: [PATCH] xfs: remove XFS_TRANS_RESERVE in collapse range

[Brian Foster <bfoster@redhat.com>]

On Thu, May 08, 2014 at 06:49:14PM +0900, Namjae Jeon wrote:
> There is no need to dip into reserve pool. Reserve pool is used for much
> more important things. And xfs_trans_reserve will never return ENOSPC
> because punch hole is already done. If we get ENOSPC, collapse range
> will be simply failed.
> 
> Signed-off-by: Namjae Jeon <namjae.jeon@samsung.com>
> Signed-off-by: Ashish Sangwan <a.sangwan@samsung.com>
> ---
>  fs/xfs/xfs_bmap_util.c | 3 +--
>  1 file changed, 1 insertion(+), 2 deletions(-)
> 
> diff --git a/fs/xfs/xfs_bmap_util.c b/fs/xfs/xfs_bmap_util.c
> index 296160b..91a43c5 100644
> --- a/fs/xfs/xfs_bmap_util.c
> +++ b/fs/xfs/xfs_bmap_util.c
> @@ -1519,7 +1519,6 @@ xfs_collapse_file_space(
>  
>  	while (!error && !done) {
>  		tp = xfs_trans_alloc(mp, XFS_TRANS_DIOSTRAT);
> -		tp->t_flags |= XFS_TRANS_RESERVE;

Makes sense.

>  		/*
>  		 * We would need to reserve permanent block for transaction.
>  		 * This will come into picture when after shifting extent into
> @@ -1529,7 +1528,7 @@ xfs_collapse_file_space(
>  		error = xfs_trans_reserve(tp, &M_RES(mp)->tr_write,
>  				XFS_DIOSTRAT_SPACE_RES(mp, 0), 0);
>  		if (error) {
> -			ASSERT(error == ENOSPC || XFS_FORCED_SHUTDOWN(mp));
> +			ASSERT(XFS_FORCED_SHUTDOWN(mp));

The xfs_trans_reserve() call still reserves XFS_DIOSTRAT_SPACE_RES()
blocks, so therefore I think ENOSPC is still a possibility. The question
is probably whether or not we need to reserve blocks for this
transaction.

Making a pass through the code... we have the possibility of deleting a
btree record in xfs_bmap_shift_extents(). This in turn could potentially
free a btree block, which frees space. I _think_ this could mean we
want to keep the block reservation because we update the free space
trees, but I suppose that could be handled by the freelist...

Perhaps Dave can confirm which direction we should go here..?

Brian

>  			xfs_trans_cancel(tp, 0);
>  			break;
>  		}
> -- 
> 1.7.11-rc0
> 
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