On Wednesday, June 05, 2013 Miao Xie wrote:
Balance will create reloc_root for each fs root, and it's going to
record last_snapshot to filter shared blocks. The side effect of
setting last_snapshot is to break nocow attributes of files.
Since the extents are not shared by the relocation tree after the balance,
we can recover the old last_snapshot safely if no one snapshoted the
source tree. We fix the above problem by this way.
This patch also fixed my problem. I tend to like this patch better as the
fix lands on disk allowing nocow to function with an older kernel after
being balanced.
Thanks,
Kyle
Tested-by: Kyle Gates <kylegates@xxxxxxxxxxx>
Reported-by: Kyle Gates <kylegates@xxxxxxxxxxx>
Signed-off-by: Liu Bo <bo.li.liu@xxxxxxxxxx>
Signed-off-by: Miao Xie <miaox@xxxxxxxxxxxxxx>
---
fs/btrfs/relocation.c | 44 ++++++++++++++++++++++++++++++++++++++++++++
1 file changed, 44 insertions(+)
diff --git a/fs/btrfs/relocation.c b/fs/btrfs/relocation.c
index 395b820..934ffe6 100644
--- a/fs/btrfs/relocation.c
+++ b/fs/btrfs/relocation.c
@@ -1305,6 +1305,7 @@ static struct btrfs_root *create_reloc_root(struct
btrfs_trans_handle *trans,
struct extent_buffer *eb;
struct btrfs_root_item *root_item;
struct btrfs_key root_key;
+ u64 last_snap = 0;
int ret;
root_item = kmalloc(sizeof(*root_item), GFP_NOFS);
@@ -1320,6 +1321,7 @@ static struct btrfs_root *create_reloc_root(struct
btrfs_trans_handle *trans,
BTRFS_TREE_RELOC_OBJECTID);
BUG_ON(ret);
+ last_snap = btrfs_root_last_snapshot(&root->root_item);
btrfs_set_root_last_snapshot(&root->root_item,
trans->transid - 1);
} else {
@@ -1345,6 +1347,12 @@ static struct btrfs_root *create_reloc_root(struct
btrfs_trans_handle *trans,
memset(&root_item->drop_progress, 0,
sizeof(struct btrfs_disk_key));
root_item->drop_level = 0;
+ /*
+ * abuse rtransid, it is safe because it is impossible to
+ * receive data into a relocation tree.
+ */
+ btrfs_set_root_rtransid(root_item, last_snap);
+ btrfs_set_root_otransid(root_item, trans->transid);
}
btrfs_tree_unlock(eb);
@@ -2273,8 +2281,12 @@ void free_reloc_roots(struct list_head *list)
static noinline_for_stack
int merge_reloc_roots(struct reloc_control *rc)
{
+ struct btrfs_trans_handle *trans;
struct btrfs_root *root;
struct btrfs_root *reloc_root;
+ u64 last_snap;
+ u64 otransid;
+ u64 objectid;
LIST_HEAD(reloc_roots);
int found = 0;
int ret = 0;
@@ -2308,12 +2320,44 @@ again:
} else {
list_del_init(&reloc_root->root_list);
}
+
+ /*
+ * we keep the old last snapshod transid in rtranid when we
+ * created the relocation tree.
+ */
+ last_snap = btrfs_root_rtransid(&reloc_root->root_item);
+ otransid = btrfs_root_otransid(&reloc_root->root_item);
+ objectid = reloc_root->root_key.offset;
+
ret = btrfs_drop_snapshot(reloc_root, rc->block_rsv, 0, 1);
if (ret < 0) {
if (list_empty(&reloc_root->root_list))
list_add_tail(&reloc_root->root_list,
&reloc_roots);
goto out;
+ } else if (!ret) {
+ /*
+ * recover the last snapshot tranid to avoid
+ * the space balance break NOCOW.
+ */
+ root = read_fs_root(rc->extent_root->fs_info,
+ objectid);
+ if (IS_ERR(root))
+ continue;
+
+ if (btrfs_root_refs(&root->root_item) == 0)
+ continue;
+
+ trans = btrfs_join_transaction(root);
+ BUG_ON(IS_ERR(trans));
+
+ /* Check if the fs/file tree was snapshoted or not. */
+ if (btrfs_root_last_snapshot(&root->root_item) ==
+ otransid - 1)
+ btrfs_set_root_last_snapshot(&root->root_item,
+ last_snap);
+
+ btrfs_end_transaction(trans, root);
}
}
--
1.8.1.4
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