Btrfs: limit the global reserve to 512mb

commit fdf30d1c1b386e1b73116cc7e0fb14e962b763b0 upstream.

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

Reported-and-tested-by: Stefan Priebe <s.priebe@profihost.ag>
Signed-off-by: Josef Bacik <jbacik@fusionio.com>
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>

diff --git a/fs/btrfs/extent-tree.c b/fs/btrfs/extent-tree.c
index f5fbe576d2baf48519a01bd449344b49edffa070..8d4d53dd3e16a0c09edbaf9e79c02bd8d02718a5 100644 (file)
--- a/fs/btrfs/extent-tree.c
+++ b/fs/btrfs/extent-tree.c
@@ -3996,7 +3996,7 @@ static void update_global_block_rsv(struct btrfs_fs_info *fs_info)
        spin_lock(&block_rsv->lock);
        spin_lock(&sinfo->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 +