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Btrfs: make fiemap not blow when you have lots of snapshots

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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>
This commit is contained in:
Josef Bacik
2014-09-10 16:20:45 -04:00
committed by Chris Mason
parent 78a017a2c9
commit dc046b10c8
3 changed files with 116 additions and 36 deletions
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40
fs/btrfs/extent_io.c
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@@ -4169,19 +4169,6 @@ static struct extent_map *get_extent_skip_holes(struct inode *inode,
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 @@ int extent_fiemap(struct inode *inode, struct fiemap_extent_info *fieinfo,
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 @@ int extent_fiemap(struct inode *inode, struct fiemap_extent_info *fieinfo,
* 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 @@ int extent_fiemap(struct inode *inode, struct fiemap_extent_info *fieinfo,
} 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;