Re: [PATCH stable v4.12 backport] Btrfs: fix early ENOSPC due to delalloc

[Chris Mason <clm@fb.com>]

Hmpf, forgot to put the sha in Linus' tree:

17024ad0a0fdfcfe53043afb969b813d3e020c21

-chris

On 08/11/2017 10:41 AM, Chris Mason wrote:
> From: Omar Sandoval <osandov@fb.com>
> 
> If a lot of metadata is reserved for outstanding delayed allocations, we
> rely on shrink_delalloc() to reclaim metadata space in order to fulfill
> reservation tickets. However, shrink_delalloc() has a shortcut where if
> it determines that space can be overcommitted, it will stop early. This
> made sense before the ticketed enospc system, but now it means that
> shrink_delalloc() will often not reclaim enough space to fulfill any
> tickets, leading to an early ENOSPC. (Reservation tickets don't care
> about being able to overcommit, they need every byte accounted for.)
> 
> Fix it by getting rid of the shortcut so that shrink_delalloc() reclaims
> all of the metadata it is supposed to. This fixes early ENOSPCs we were
> seeing when doing a btrfs receive to populate a new filesystem, as well
> as early ENOSPCs Christoph saw when doing a big cp -r onto Btrfs.
> 
> Fixes: 957780eb2788 ("Btrfs: introduce ticketed enospc infrastructure")
> Tested-by: Christoph Anton Mitterer <mail@christoph.anton.mitterer.name>
> Cc: stable@vger.kernel.org
> Reviewed-by: Josef Bacik <jbacik@fb.com>
> Signed-off-by: Omar Sandoval <osandov@fb.com>
> Signed-off-by: David Sterba <dsterba@suse.com>
> Signed-off-by: Chris Mason <clm@fb.com>
> ---
>   fs/btrfs/extent-tree.c | 4 ----
>   1 file changed, 4 deletions(-)
> 
> diff --git a/fs/btrfs/extent-tree.c b/fs/btrfs/extent-tree.c
> index 33d979e9..83eecd3 100644
> --- a/fs/btrfs/extent-tree.c
> +++ b/fs/btrfs/extent-tree.c
> @@ -4776,10 +4776,6 @@ static void shrink_delalloc(struct btrfs_root *root, u64 to_reclaim, u64 orig,
>   		else
>   			flush = BTRFS_RESERVE_NO_FLUSH;
>   		spin_lock(&space_info->lock);
> -		if (can_overcommit(root, space_info, orig, flush)) {
> -			spin_unlock(&space_info->lock);
> -			break;
> -		}
>   		if (list_empty(&space_info->tickets) &&
>   		    list_empty(&space_info->priority_tickets)) {
>   			spin_unlock(&space_info->lock);
>