btrfs: fiemap: preallocate ulists for btrfs_check_shared

btrfs_check_shared looks up parents of a given extent and uses ulists
for that. These are allocated and freed repeatedly. Preallocation in the
caller will avoid the overhead and also allow us to use the GFP_KERNEL
as it is happens before the extent locks are taken.

Reviewed-by: Nikolay Borisov <nborisov@suse.com>
Reviewed-by: Filipe Manana <fdmanana@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>

fs/btrfs/backref.c

@@ -1465,12 +1465,11 @@ int btrfs_find_all_roots(struct btrfs_trans_handle *trans,
  *
  * Return: 0 if extent is not shared, 1 if it is shared, < 0 on error.
  */
-int btrfs_check_shared(struct btrfs_root *root, u64 inum, u64 bytenr)
+int btrfs_check_shared(struct btrfs_root *root, u64 inum, u64 bytenr,
+		struct ulist *roots, struct ulist *tmp)
 {
 	struct btrfs_fs_info *fs_info = root->fs_info;
 	struct btrfs_trans_handle *trans;
-	struct ulist *tmp = NULL;
-	struct ulist *roots = NULL;
 	struct ulist_iterator uiter;
 	struct ulist_node *node;
 	struct seq_list elem = SEQ_LIST_INIT(elem);
@@ -1481,12 +1480,8 @@ int btrfs_check_shared(struct btrfs_root *root, u64 inum, u64 bytenr)
 		.share_count = 0,
 	};
 
-	tmp = ulist_alloc(GFP_NOFS);
-	roots = ulist_alloc(GFP_NOFS);
-	if (!tmp || !roots) {
-		ret = -ENOMEM;
-		goto out;
-	}
+	ulist_init(roots);
+	ulist_init(tmp);
 
 	trans = btrfs_attach_transaction(root);
 	if (IS_ERR(trans)) {
@@ -1527,8 +1522,8 @@ int btrfs_check_shared(struct btrfs_root *root, u64 inum, u64 bytenr)
 		up_read(&fs_info->commit_root_sem);
 	}
 out:
-	ulist_free(tmp);
-	ulist_free(roots);
+	ulist_release(roots);
+	ulist_release(tmp);
 	return ret;
 }
 

fs/btrfs/backref.h

@@ -57,7 +57,8 @@ 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_root *root, u64 inum, u64 bytenr);
+int btrfs_check_shared(struct btrfs_root *root, u64 inum, u64 bytenr,
+		struct ulist *roots, struct ulist *tmp_ulist);
 
 int __init btrfs_prelim_ref_init(void);
 void __cold btrfs_prelim_ref_exit(void);

fs/btrfs/extent_io.c

@@ -4542,6 +4542,8 @@ int extent_fiemap(struct inode *inode, struct fiemap_extent_info *fieinfo,
 	struct btrfs_path *path;
 	struct btrfs_root *root = BTRFS_I(inode)->root;
 	struct fiemap_cache cache = { 0 };
+	struct ulist *roots;
+	struct ulist *tmp_ulist;
 	int end = 0;
 	u64 em_start = 0;
 	u64 em_len = 0;
@@ -4555,6 +4557,13 @@ int extent_fiemap(struct inode *inode, struct fiemap_extent_info *fieinfo,
 		return -ENOMEM;
 	path->leave_spinning = 1;
 
+	roots = ulist_alloc(GFP_KERNEL);
+	tmp_ulist = ulist_alloc(GFP_KERNEL);
+	if (!roots || !tmp_ulist) {
+		ret = -ENOMEM;
+		goto out_free_ulist;
+	}
+
 	start = round_down(start, btrfs_inode_sectorsize(inode));
 	len = round_up(max, btrfs_inode_sectorsize(inode)) - start;
 
@@ -4566,7 +4575,7 @@ int extent_fiemap(struct inode *inode, struct fiemap_extent_info *fieinfo,
 			btrfs_ino(BTRFS_I(inode)), -1, 0);
 	if (ret < 0) {
 		btrfs_free_path(path);
-		return ret;
+		goto out_free_ulist;
 	} else {
 		WARN_ON(!ret);
 		if (ret == 1)
@@ -4675,7 +4684,7 @@ int extent_fiemap(struct inode *inode, struct fiemap_extent_info *fieinfo,
 			 */
 			ret = btrfs_check_shared(root,
 						 btrfs_ino(BTRFS_I(inode)),
-						 bytenr);
+						 bytenr, roots, tmp_ulist);
 			if (ret < 0)
 				goto out_free;
 			if (ret)
@@ -4721,6 +4730,10 @@ int extent_fiemap(struct inode *inode, struct fiemap_extent_info *fieinfo,
 	btrfs_free_path(path);
 	unlock_extent_cached(&BTRFS_I(inode)->io_tree, start, start + len - 1,
 			     &cached_state);
+
+out_free_ulist:
+	ulist_free(roots);
+	ulist_free(tmp_ulist);
 	return ret;
 }