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

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

[Chris Mason]

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);
-- 
2.9.3

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

[Chris Mason]

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);
> 

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

[Chris Mason]

On 08/11/2017 10:44 AM, Chris Mason wrote:
> Hmpf, forgot to put the sha in Linus' tree:
> 
> 17024ad0a0fdfcfe53043afb969b813d3e020c21
>

And Nikolay just reminded me this is already in Greg's queue.  Whoops.

-chris