From: Wang Xiaoguang <wangxg.f...@cn.fujitsu.com>
In btrfs_delalloc_reserve_metadata(), the number of metadata bytes we try
to reserve is calculated by the difference between outstanding_extents and
reserved_extents.
When reserve_metadata_bytes() fails to reserve desited metadata space,
it has already done some reclaim work, such as write ordered extents.
In that case, outstanding_extents and reserved_extents may already
changed, and we may reserve enough metadata space then.
So this patch will try to call reserve_metadata_bytes() at most 3 times
to ensure we really run out of space.
Such false ENOSPC is mainly caused by small file extents and time
consuming delalloc functions, which mainly affects in-band
de-duplication. (Compress should also be affected, but LZO/zlib is
faster than SHA256, so still harder to trigger than dedup).
Signed-off-by: Wang Xiaoguang <wangxg.f...@cn.fujitsu.com>
---
fs/btrfs/extent-tree.c | 23 +++++++++++++++++++++--
1 file changed, 21 insertions(+), 2 deletions(-)
diff --git a/fs/btrfs/extent-tree.c b/fs/btrfs/extent-tree.c
index 2a17c88..c60e24a 100644
--- a/fs/btrfs/extent-tree.c
+++ b/fs/btrfs/extent-tree.c
@@ -5669,6 +5669,7 @@ int btrfs_delalloc_reserve_metadata(struct inode *inode,
u64 num_bytes)
bool delalloc_lock = true;
u64 to_free = 0;
unsigned dropped;
+ int loops = 0;
/* If we are a free space inode we need to not flush since we will be in
* the middle of a transaction commit. We also don't need the delalloc
@@ -5684,11 +5685,12 @@ int btrfs_delalloc_reserve_metadata(struct inode
*inode, u64 num_bytes)
btrfs_transaction_in_commit(root->fs_info))
schedule_timeout(1);
+ num_bytes = ALIGN(num_bytes, root->sectorsize);
+
+again:
if (delalloc_lock)
mutex_lock(&BTRFS_I(inode)->delalloc_mutex);
- num_bytes = ALIGN(num_bytes, root->sectorsize);
-
spin_lock(&BTRFS_I(inode)->lock);
nr_extents = (unsigned)div64_u64(num_bytes +
BTRFS_MAX_EXTENT_SIZE - 1,
@@ -5809,6 +5811,23 @@ out_fail:
}
if (delalloc_lock)
mutex_unlock(&BTRFS_I(inode)->delalloc_mutex);
+ /*
+ * The number of metadata bytes is calculated by the difference
+ * between outstanding_extents and reserved_extents. Sometimes though
+ * reserve_metadata_bytes() fails to reserve the wanted metadata bytes,
+ * indeed it has already done some work to reclaim metadata space, hence
+ * both outstanding_extents and reserved_extents would have changed and
+ * the bytes we try to reserve would also has changed(may be smaller).
+ * So here we try to reserve again. This is much useful for online
+ * dedup, which will easily eat almost all meta space.
+ *
+ * XXX: Indeed here 3 is arbitrarily choosed, it's a good workaround for
+ * online dedup, later we should find a better method to avoid dedup
+ * enospc issue.
+ */
+ if (unlikely(ret == -ENOSPC && loops++ < 3))
+ goto again;
+
return ret;
}
--
2.7.1
--
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