Btrfs: make fiemap not blow when you have lots of snapshots
We have been iterating all references for each extent we have in a file when we
do fiemap to see if it is shared. This is fine when you have a few clones or a
few snapshots, but when you have 5k snapshots suddenly fiemap just sits there
and stares at you. So add btrfs_check_shared which will use the backref walking
code but will short circuit as soon as it finds a root or inode that doesn't
match the one we currently have. This makes fiemap on my testbox go from
looking at me blankly for a day to spitting out actual output in a reasonable
amount of time. Thanks,
Signed-off-by: Josef Bacik <jbacik@fb.com>
Signed-off-by: Chris Mason <clm@fb.com>
diff --git a/fs/btrfs/extent_io.c b/fs/btrfs/extent_io.c
index d70feb5..d5e71d4 100644
--- a/fs/btrfs/extent_io.c
+++ b/fs/btrfs/extent_io.c
@@ -4169,19 +4169,6 @@
return NULL;
}
-static noinline int count_ext_ref(u64 inum, u64 offset, u64 root_id, void *ctx)
-{
- unsigned long cnt = *((unsigned long *)ctx);
-
- cnt++;
- *((unsigned long *)ctx) = cnt;
-
- /* Now we're sure that the extent is shared. */
- if (cnt > 1)
- return 1;
- return 0;
-}
-
int extent_fiemap(struct inode *inode, struct fiemap_extent_info *fieinfo,
__u64 start, __u64 len, get_extent_t *get_extent)
{
@@ -4198,6 +4185,7 @@
struct extent_map *em = NULL;
struct extent_state *cached_state = NULL;
struct btrfs_path *path;
+ struct btrfs_root *root = BTRFS_I(inode)->root;
int end = 0;
u64 em_start = 0;
u64 em_len = 0;
@@ -4218,8 +4206,8 @@
* lookup the last file extent. We're not using i_size here
* because there might be preallocation past i_size
*/
- ret = btrfs_lookup_file_extent(NULL, BTRFS_I(inode)->root,
- path, btrfs_ino(inode), -1, 0);
+ ret = btrfs_lookup_file_extent(NULL, root, path, btrfs_ino(inode), -1,
+ 0);
if (ret < 0) {
btrfs_free_path(path);
return ret;
@@ -4312,25 +4300,27 @@
} else if (em->block_start == EXTENT_MAP_DELALLOC) {
flags |= (FIEMAP_EXTENT_DELALLOC |
FIEMAP_EXTENT_UNKNOWN);
- } else {
- unsigned long ref_cnt = 0;
+ } else if (fieinfo->fi_extents_max) {
+ u64 bytenr = em->block_start -
+ (em->start - em->orig_start);
disko = em->block_start + offset_in_extent;
/*
* As btrfs supports shared space, this information
* can be exported to userspace tools via
- * flag FIEMAP_EXTENT_SHARED.
+ * flag FIEMAP_EXTENT_SHARED. If fi_extents_max == 0
+ * then we're just getting a count and we can skip the
+ * lookup stuff.
*/
- ret = iterate_inodes_from_logical(
- em->block_start,
- BTRFS_I(inode)->root->fs_info,
- path, count_ext_ref, &ref_cnt);
- if (ret < 0 && ret != -ENOENT)
+ ret = btrfs_check_shared(NULL, root->fs_info,
+ root->objectid,
+ btrfs_ino(inode), bytenr);
+ if (ret < 0)
goto out_free;
-
- if (ref_cnt > 1)
+ if (ret)
flags |= FIEMAP_EXTENT_SHARED;
+ ret = 0;
}
if (test_bit(EXTENT_FLAG_COMPRESSED, &em->flags))
flags |= FIEMAP_EXTENT_ENCODED;