[PATCH v6 19/19] btrfs: try more times to alloc metadata reserve space
From: Qu Wenruo <hidden>
Date: 2016-02-05 01:25:03
Subsystem:
btrfs file system, filesystems (vfs and infrastructure), the rest · Maintainers:
Chris Mason, David Sterba, Alexander Viro, Christian Brauner, Linus Torvalds
From: Wang Xiaoguang <redacted> 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 <redacted> --- 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; }
--
2.7.0