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>

3 files changed, 116 insertions, 36 deletions

diff --git a/fs/btrfs/backref.c b/fs/btrfs/backref.c
index 4de97926939e..6829dc5aa657 100644
--- a/fs/btrfs/backref.c
+++ b/fs/btrfs/backref.c
@@ -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;
@@ -377,7 +380,8 @@ out:
 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;
@@ -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);
@@ -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;
@@ -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);
@@ -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;
@@ -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);
@@ -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;
@@ -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);
@@ -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;
@@ -929,7 +961,8 @@ again:
                         }
                         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;
@@ -951,11 +984,11 @@ again:
                      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;
                 }
@@ -971,7 +1004,8 @@ again:
         __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;
 
@@ -981,6 +1015,11 @@ again:
                 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)
@@ -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;
@@ -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);
@@ -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)
  */
diff --git a/fs/btrfs/backref.h b/fs/btrfs/backref.h
index 86fc20fec282..2a1ac6bfc724 100644
--- a/fs/btrfs/backref.h
+++ b/fs/btrfs/backref.h
@@ -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);
diff --git a/fs/btrfs/extent_io.c b/fs/btrfs/extent_io.c
index d70feb545066..d5e71d4646dd 100644
--- a/fs/btrfs/extent_io.c
+++ b/fs/btrfs/extent_io.c
@@ -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;