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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>
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Josef Bacik authored and Chris Mason committed Sep 17, 2014
1 parent 78a017a commit dc046b1
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Showing 3 changed files with 116 additions and 36 deletions.
109 changes: 98 additions & 11 deletions fs/btrfs/backref.c
View file
Original file line number Diff line number Diff line change
Expand Up @@ -25,6 +25,9 @@
#include "delayed-ref.h"
#include "locking.h"

/* Just an arbitrary number so we can be sure this happened */
#define BACKREF_FOUND_SHARED 6

struct extent_inode_elem {
u64 inum;
u64 offset;
Expand Down Expand Up @@ -377,7 +380,8 @@ static int __resolve_indirect_ref(struct btrfs_fs_info *fs_info,
static int __resolve_indirect_refs(struct btrfs_fs_info *fs_info,
struct btrfs_path *path, u64 time_seq,
struct list_head *head,
const u64 *extent_item_pos, u64 total_refs)
const u64 *extent_item_pos, u64 total_refs,
u64 root_objectid)
{
int err;
int ret = 0;
Expand All @@ -402,6 +406,10 @@ static int __resolve_indirect_refs(struct btrfs_fs_info *fs_info,
continue;
if (ref->count == 0)
continue;
if (root_objectid && ref->root_id != root_objectid) {
ret = BACKREF_FOUND_SHARED;
goto out;
}
err = __resolve_indirect_ref(fs_info, path, time_seq, ref,
parents, extent_item_pos,
total_refs);
Expand Down Expand Up @@ -561,7 +569,8 @@ static void __merge_refs(struct list_head *head, int mode)
* smaller or equal that seq to the list
*/
static int __add_delayed_refs(struct btrfs_delayed_ref_head *head, u64 seq,
struct list_head *prefs, u64 *total_refs)
struct list_head *prefs, u64 *total_refs,
u64 inum)
{
struct btrfs_delayed_extent_op *extent_op = head->extent_op;
struct rb_node *n = &head->node.rb_node;
Expand Down Expand Up @@ -625,6 +634,16 @@ static int __add_delayed_refs(struct btrfs_delayed_ref_head *head, u64 seq,
key.objectid = ref->objectid;
key.type = BTRFS_EXTENT_DATA_KEY;
key.offset = ref->offset;

/*
* Found a inum that doesn't match our known inum, we
* know it's shared.
*/
if (inum && ref->objectid != inum) {
ret = BACKREF_FOUND_SHARED;
break;
}

ret = __add_prelim_ref(prefs, ref->root, &key, 0, 0,
node->bytenr,
node->ref_mod * sgn, GFP_ATOMIC);
Expand Down Expand Up @@ -659,7 +678,7 @@ static int __add_delayed_refs(struct btrfs_delayed_ref_head *head, u64 seq,
static int __add_inline_refs(struct btrfs_fs_info *fs_info,
struct btrfs_path *path, u64 bytenr,
int *info_level, struct list_head *prefs,
u64 *total_refs)
u64 *total_refs, u64 inum)
{
int ret = 0;
int slot;
Expand Down Expand Up @@ -744,6 +763,12 @@ static int __add_inline_refs(struct btrfs_fs_info *fs_info,
dref);
key.type = BTRFS_EXTENT_DATA_KEY;
key.offset = btrfs_extent_data_ref_offset(leaf, dref);

if (inum && key.objectid != inum) {
ret = BACKREF_FOUND_SHARED;
break;
}

root = btrfs_extent_data_ref_root(leaf, dref);
ret = __add_prelim_ref(prefs, root, &key, 0, 0,
bytenr, count, GFP_NOFS);
Expand All @@ -765,7 +790,7 @@ static int __add_inline_refs(struct btrfs_fs_info *fs_info,
*/
static int __add_keyed_refs(struct btrfs_fs_info *fs_info,
struct btrfs_path *path, u64 bytenr,
int info_level, struct list_head *prefs)
int info_level, struct list_head *prefs, u64 inum)
{
struct btrfs_root *extent_root = fs_info->extent_root;
int ret;
Expand Down Expand Up @@ -827,6 +852,12 @@ static int __add_keyed_refs(struct btrfs_fs_info *fs_info,
dref);
key.type = BTRFS_EXTENT_DATA_KEY;
key.offset = btrfs_extent_data_ref_offset(leaf, dref);

if (inum && key.objectid != inum) {
ret = BACKREF_FOUND_SHARED;
break;
}

root = btrfs_extent_data_ref_root(leaf, dref);
ret = __add_prelim_ref(prefs, root, &key, 0, 0,
bytenr, count, GFP_NOFS);
Expand Down Expand Up @@ -854,7 +885,8 @@ static int __add_keyed_refs(struct btrfs_fs_info *fs_info,
static int find_parent_nodes(struct btrfs_trans_handle *trans,
struct btrfs_fs_info *fs_info, u64 bytenr,
u64 time_seq, struct ulist *refs,
struct ulist *roots, const u64 *extent_item_pos)
struct ulist *roots, const u64 *extent_item_pos,
u64 root_objectid, u64 inum)
{
struct btrfs_key key;
struct btrfs_path *path;
Expand Down Expand Up @@ -929,7 +961,8 @@ static int find_parent_nodes(struct btrfs_trans_handle *trans,
}
spin_unlock(&delayed_refs->lock);
ret = __add_delayed_refs(head, time_seq,
&prefs_delayed, &total_refs);
&prefs_delayed, &total_refs,
inum);
mutex_unlock(&head->mutex);
if (ret)
goto out;
Expand All @@ -951,11 +984,11 @@ static int find_parent_nodes(struct btrfs_trans_handle *trans,
key.type == BTRFS_METADATA_ITEM_KEY)) {
ret = __add_inline_refs(fs_info, path, bytenr,
&info_level, &prefs,
&total_refs);
&total_refs, inum);
if (ret)
goto out;
ret = __add_keyed_refs(fs_info, path, bytenr,
info_level, &prefs);
info_level, &prefs, inum);
if (ret)
goto out;
}
Expand All @@ -971,7 +1004,8 @@ static int find_parent_nodes(struct btrfs_trans_handle *trans,
__merge_refs(&prefs, 1);

ret = __resolve_indirect_refs(fs_info, path, time_seq, &prefs,
extent_item_pos, total_refs);
extent_item_pos, total_refs,
root_objectid);
if (ret)
goto out;

Expand All @@ -981,6 +1015,11 @@ static int find_parent_nodes(struct btrfs_trans_handle *trans,
ref = list_first_entry(&prefs, struct __prelim_ref, list);
WARN_ON(ref->count < 0);
if (roots && ref->count && ref->root_id && ref->parent == 0) {
if (root_objectid && ref->root_id != root_objectid) {
ret = BACKREF_FOUND_SHARED;
goto out;
}

/* no parent == root of tree */
ret = ulist_add(roots, ref->root_id, 0, GFP_NOFS);
if (ret < 0)
Expand Down Expand Up @@ -1087,7 +1126,7 @@ static int btrfs_find_all_leafs(struct btrfs_trans_handle *trans,
return -ENOMEM;

ret = find_parent_nodes(trans, fs_info, bytenr,
time_seq, *leafs, NULL, extent_item_pos);
time_seq, *leafs, NULL, extent_item_pos, 0, 0);
if (ret < 0 && ret != -ENOENT) {
free_leaf_list(*leafs);
return ret;
Expand Down Expand Up @@ -1130,7 +1169,7 @@ static int __btrfs_find_all_roots(struct btrfs_trans_handle *trans,
ULIST_ITER_INIT(&uiter);
while (1) {
ret = find_parent_nodes(trans, fs_info, bytenr,
time_seq, tmp, *roots, NULL);
time_seq, tmp, *roots, NULL, 0, 0);
if (ret < 0 && ret != -ENOENT) {
ulist_free(tmp);
ulist_free(*roots);
Expand Down Expand Up @@ -1161,6 +1200,54 @@ int btrfs_find_all_roots(struct btrfs_trans_handle *trans,
return ret;
}

int btrfs_check_shared(struct btrfs_trans_handle *trans,
struct btrfs_fs_info *fs_info, u64 root_objectid,
u64 inum, u64 bytenr)
{
struct ulist *tmp = NULL;
struct ulist *roots = NULL;
struct ulist_iterator uiter;
struct ulist_node *node;
struct seq_list elem = {};
int ret = 0;

tmp = ulist_alloc(GFP_NOFS);
roots = ulist_alloc(GFP_NOFS);
if (!tmp || !roots) {
ulist_free(tmp);
ulist_free(roots);
return -ENOMEM;
}

if (trans)
btrfs_get_tree_mod_seq(fs_info, &elem);
else
down_read(&fs_info->commit_root_sem);
ULIST_ITER_INIT(&uiter);
while (1) {
ret = find_parent_nodes(trans, fs_info, bytenr, elem.seq, tmp,
roots, NULL, root_objectid, inum);
if (ret == BACKREF_FOUND_SHARED) {
ret = 1;
break;
}
if (ret < 0 && ret != -ENOENT)
break;
node = ulist_next(tmp, &uiter);
if (!node)
break;
bytenr = node->val;
cond_resched();
}
if (trans)
btrfs_put_tree_mod_seq(fs_info, &elem);
else
up_read(&fs_info->commit_root_sem);
ulist_free(tmp);
ulist_free(roots);
return ret;
}

/*
* this makes the path point to (inum INODE_ITEM ioff)
*/
Expand Down
3 changes: 3 additions & 0 deletions fs/btrfs/backref.h
View file
Original file line number Diff line number Diff line change
Expand Up @@ -71,6 +71,9 @@ int btrfs_find_one_extref(struct btrfs_root *root, u64 inode_objectid,
u64 start_off, struct btrfs_path *path,
struct btrfs_inode_extref **ret_extref,
u64 *found_off);
int btrfs_check_shared(struct btrfs_trans_handle *trans,
struct btrfs_fs_info *fs_info, u64 root_objectid,
u64 inum, u64 bytenr);

int __init btrfs_prelim_ref_init(void);
void btrfs_prelim_ref_exit(void);
Expand Down
40 changes: 15 additions & 25 deletions fs/btrfs/extent_io.c
View file
Original file line number Diff line number Diff line change
Expand Up @@ -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)
{
Expand All @@ -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;
Expand All @@ -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;
Expand Down Expand Up @@ -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;
Expand Down

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