diff options
authorFilipe Manana <fdmanana@suse.com>2015-11-13 23:57:17 +0000
committerChris Mason <clm@fb.com>2015-11-25 05:19:50 -0800
commit7fd01182d1a1412cd44a5474b9aa93548d4a73ae (patch)
parentBtrfs: use global reserve when deleting unused block group after ENOSPC (diff)
Btrfs: fix the number of transaction units needed to remove a block group
We were using only 1 transaction unit when attempting to delete an unused block group but in reality we need 3 + N units, where N corresponds to the number of stripes. We were accounting only for the addition of the orphan item (for the block group's free space cache inode) but we were not accounting that we need to delete one block group item from the extent tree, one free space item from the tree of tree roots and N device extent items from the device tree. While one unit is not enough, it worked most of the time because for each single unit we are too pessimistic and assume an entire tree path, with the highest possible heigth (8), needs to be COWed with eventual node splits at every possible level in the tree, so there was usually enough reserved space for removing all the items and adding the orphan item. However after adding the orphan item, writepages() can by called by the VM subsystem against the btree inode when we are under memory pressure, which causes writeback to start for the nodes we COWed before, this forces the operation to remove the free space item to COW again some (or all of) the same nodes (in the tree of tree roots). Even without writepages() being called, we could fail with ENOSPC because these items are located in multiple trees and one of them might have a higher heigth and require node/leaf splits at many levels, exhausting all the reserved space before removing all the items and adding the orphan. In the kernel 4.0 release, commit 3d84be799194 ("Btrfs: fix BUG_ON in btrfs_orphan_add() when delete unused block group"), we attempted to fix a BUG_ON due to ENOSPC when trying to add the orphan item by making the cleaner kthread reserve one transaction unit before attempting to remove the block group, but this was not enough. We had a couple user reports still hitting the same BUG_ON after 4.0, like Stefan Priebe's report on a 4.2-rc6 kernel for example: http://www.spinics.net/lists/linux-btrfs/msg46070.html So fix this by reserving all the necessary units of metadata. Reported-by: Stefan Priebe <s.priebe@profihost.ag> Fixes: 3d84be799194 ("Btrfs: fix BUG_ON in btrfs_orphan_add() when delete unused block group") Signed-off-by: Filipe Manana <fdmanana@suse.com> Signed-off-by: Chris Mason <clm@fb.com>
3 files changed, 38 insertions, 5 deletions
diff --git a/fs/btrfs/ctree.h b/fs/btrfs/ctree.h
index 1573be6f9518..d88994f71eae 100644
--- a/fs/btrfs/ctree.h
+++ b/fs/btrfs/ctree.h
@@ -3480,7 +3480,8 @@ int btrfs_make_block_group(struct btrfs_trans_handle *trans,
u64 type, u64 chunk_objectid, u64 chunk_offset,
u64 size);
struct btrfs_trans_handle *btrfs_start_trans_remove_block_group(
- struct btrfs_fs_info *fs_info);
+ struct btrfs_fs_info *fs_info,
+ const u64 chunk_offset);
int btrfs_remove_block_group(struct btrfs_trans_handle *trans,
struct btrfs_root *root, u64 group_start,
struct extent_map *em);
diff --git a/fs/btrfs/extent-tree.c b/fs/btrfs/extent-tree.c
index 78200932c1cf..e97d6d61cd42 100644
--- a/fs/btrfs/extent-tree.c
+++ b/fs/btrfs/extent-tree.c
@@ -10257,14 +10257,44 @@ out:
struct btrfs_trans_handle *
-btrfs_start_trans_remove_block_group(struct btrfs_fs_info *fs_info)
+btrfs_start_trans_remove_block_group(struct btrfs_fs_info *fs_info,
+ const u64 chunk_offset)
+ struct extent_map_tree *em_tree = &fs_info->mapping_tree.map_tree;
+ struct extent_map *em;
+ struct map_lookup *map;
+ unsigned int num_items;
+ read_lock(&em_tree->lock);
+ em = lookup_extent_mapping(em_tree, chunk_offset, 1);
+ read_unlock(&em_tree->lock);
+ ASSERT(em && em->start == chunk_offset);
+ * We need to reserve 3 + N units from the metadata space info in order
+ * to remove a block group (done at btrfs_remove_chunk() and at
+ * btrfs_remove_block_group()), which are used for:
+ *
* 1 unit for adding the free space inode's orphan (located in the tree
* of tree roots).
+ * 1 unit for deleting the block group item (located in the extent
+ * tree).
+ * 1 unit for deleting the free space item (located in tree of tree
+ * roots).
+ * N units for deleting N device extent items corresponding to each
+ * stripe (located in the device tree).
+ *
+ * In order to remove a block group we also need to reserve units in the
+ * system space info in order to update the chunk tree (update one or
+ * more device items and remove one chunk item), but this is done at
+ * btrfs_remove_chunk() through a call to check_system_chunk().
+ map = (struct map_lookup *)em->bdev;
+ num_items = 3 + map->num_stripes;
+ free_extent_map(em);
return btrfs_start_transaction_fallback_global_rsv(fs_info->extent_root,
- 1, 1);
+ num_items, 1);
@@ -10333,7 +10363,8 @@ void btrfs_delete_unused_bgs(struct btrfs_fs_info *fs_info)
* Want to do this before we do anything else so we can recover
* properly if we fail to join the transaction.
- trans = btrfs_start_trans_remove_block_group(fs_info);
+ trans = btrfs_start_trans_remove_block_group(fs_info,
+ block_group->key.objectid);
if (IS_ERR(trans)) {
btrfs_dec_block_group_ro(root, block_group);
ret = PTR_ERR(trans);
diff --git a/fs/btrfs/volumes.c b/fs/btrfs/volumes.c
index e0bd364e958d..45f20252efed 100644
--- a/fs/btrfs/volumes.c
+++ b/fs/btrfs/volumes.c
@@ -2853,7 +2853,8 @@ static int btrfs_relocate_chunk(struct btrfs_root *root, u64 chunk_offset)
if (ret)
return ret;
- trans = btrfs_start_trans_remove_block_group(root->fs_info);
+ trans = btrfs_start_trans_remove_block_group(root->fs_info,
+ chunk_offset);
if (IS_ERR(trans)) {
ret = PTR_ERR(trans);
btrfs_std_error(root->fs_info, ret, NULL);