Btrfs devel - Mar 2013 - [PATCH] Btrfs: limit the global reserve to 512mb

A user reported a problem where he was getting early ENOSPC with hundreds of
gigs of free data space and 6 gigs of free metadata space.  This is because the
global block reserve was taking up the entire free metadata space.  This is
ridiculous, we have infrastructure in place to throttle if we start using too
much of the global reserve, so instead of letting it get this huge just limit it
to 512mb so that users can still get work done.  This allowed the user to
complete his rsync without issues.  Thanks

Cc: stable@vger.kernel.org
Reported-and-tested-by: Stefan Priebe <s.priebe@profihost.ag>
Signed-off-by: Josef Bacik <jbacik@fusionio.com>
---
 fs/btrfs/extent-tree.c |    2 +-
 1 files changed, 1 insertions(+), 1 deletions(-)

diff --git a/fs/btrfs/extent-tree.c b/fs/btrfs/extent-tree.c
index c08c7c8..5791da2 100644
--- a/fs/btrfs/extent-tree.c
+++ b/fs/btrfs/extent-tree.c
@@ -4554,7 +4554,7 @@ static void update_global_block_rsv(struct btrfs_fs_info
*fs_info)
 	spin_lock(&sinfo->lock);
 	spin_lock(&block_rsv->lock);
 
-	block_rsv->size = num_bytes;
+	block_rsv->size = min_t(u64, num_bytes, 512 * 1024 * 1024);
 
 	num_bytes = sinfo->bytes_used + sinfo->bytes_pinned +
 		    sinfo->bytes_reserved + sinfo->bytes_readonly +
-- 
1.7.7.6

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On Tue, 26 Mar 2013 15:34:06 -0400
Josef Bacik <jbacik@fusionio.com> wrote:
> A user reported a problem where he was getting early ENOSPC with hundreds
of
> gigs of free data space and 6 gigs of free metadata space.  This is because
the
> global block reserve was taking up the entire free metadata space.  This is
> ridiculous, we have infrastructure in place to throttle if we start using
too
> much of the global reserve, so instead of letting it get this huge just
limit it
> to 512mb so that users can still get work done.  This allowed the user to
> complete his rsync without issues.  Thanks
Just a note, I added this to 3.7.10 and was able to complete a balance on a
"difficult" filesystem (60GB in size, used for /home, with creation
and
deletion of snapshots by cron), that was otherwise seeming to loop/hang
and continuously spewing -28 errors into dmesg.
> Cc: stable@vger.kernel.org
> Reported-and-tested-by: Stefan Priebe <s.priebe@profihost.ag>
> Signed-off-by: Josef Bacik <jbacik@fusionio.com>
> ---
>  fs/btrfs/extent-tree.c |    2 +-
>  1 files changed, 1 insertions(+), 1 deletions(-)
> 
> diff --git a/fs/btrfs/extent-tree.c b/fs/btrfs/extent-tree.c
> index c08c7c8..5791da2 100644
> --- a/fs/btrfs/extent-tree.c
> +++ b/fs/btrfs/extent-tree.c
> @@ -4554,7 +4554,7 @@ static void update_global_block_rsv(struct
btrfs_fs_info *fs_info)
>  	spin_lock(&sinfo->lock);
>  	spin_lock(&block_rsv->lock);
>  
> -	block_rsv->size = num_bytes;
> +	block_rsv->size = min_t(u64, num_bytes, 512 * 1024 * 1024);
>  
>  	num_bytes = sinfo->bytes_used + sinfo->bytes_pinned +
>  		    sinfo->bytes_reserved + sinfo->bytes_readonly +

-- 
With respect,
Roman