ocfs2: reflink: fix slow unlink for refcounted file

When running ocfs2 test suite multiple nodes reflink stress test, for a
4 nodes cluster, every unlink() for refcounted file needs about 700s.

The slow unlink is caused by the contention of refcount tree lock since
all nodes are unlink files using the same refcount tree.  When the
unlinking file have many extents(over 1600 in our test), most of the
extents has refcounted flag set.  In ocfs2_commit_truncate(), it will
execute the following call trace for every extents.  This means it needs
get and released refcount tree lock about 1600 times.  And when several
nodes are do this at the same time, the performance will be very low.

  ocfs2_remove_btree_range()
  --  ocfs2_lock_refcount_tree()
  ----  ocfs2_refcount_lock()
  ------  __ocfs2_cluster_lock()

ocfs2_refcount_lock() is costly, move it to ocfs2_commit_truncate() to
do lock/unlock once can improve a lot performance.
Signed-off-by: Junxiao Bi <junxiao.bi@oracle.com>
Cc: Wengang <wen.gang.wang@oracle.com>
Reviewed-by: Mark Fasheh <mfasheh@suse.de>
Cc: Joel Becker <jlbec@evilplan.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

fs/ocfs2/alloc.c

@@ -5662,7 +5662,7 @@ int ocfs2_remove_btree_range(struct inode *inode,
 			     struct ocfs2_extent_tree *et,
 			     u32 cpos, u32 phys_cpos, u32 len, int flags,
 			     struct ocfs2_cached_dealloc_ctxt *dealloc,
-			     u64 refcount_loc)
+			     u64 refcount_loc, bool refcount_tree_locked)
 {
 	int ret, credits = 0, extra_blocks = 0;
 	u64 phys_blkno = ocfs2_clusters_to_blocks(inode->i_sb, phys_cpos);
@@ -5676,12 +5676,14 @@ int ocfs2_remove_btree_range(struct inode *inode,
 		BUG_ON(!(OCFS2_I(inode)->ip_dyn_features &
 			 OCFS2_HAS_REFCOUNT_FL));
 
+		if (!refcount_tree_locked) {
 			ret = ocfs2_lock_refcount_tree(osb, refcount_loc, 1,
 						       &ref_tree, NULL);
 			if (ret) {
 				mlog_errno(ret);
 				goto bail;
 			}
+		}
 
 		ret = ocfs2_prepare_refcount_change_for_del(inode,
 							    refcount_loc,
@@ -7021,6 +7023,7 @@ int ocfs2_commit_truncate(struct ocfs2_super *osb,
 	u64 refcount_loc = le64_to_cpu(di->i_refcount_loc);
 	struct ocfs2_extent_tree et;
 	struct ocfs2_cached_dealloc_ctxt dealloc;
+	struct ocfs2_refcount_tree *ref_tree = NULL;
 
 	ocfs2_init_dinode_extent_tree(&et, INODE_CACHE(inode), di_bh);
 	ocfs2_init_dealloc_ctxt(&dealloc);
@@ -7130,9 +7133,18 @@ int ocfs2_commit_truncate(struct ocfs2_super *osb,
 
 	phys_cpos = ocfs2_blocks_to_clusters(inode->i_sb, blkno);
 
+	if ((flags & OCFS2_EXT_REFCOUNTED) && trunc_len && !ref_tree) {
+		status = ocfs2_lock_refcount_tree(osb, refcount_loc, 1,
+				&ref_tree, NULL);
+		if (status) {
+			mlog_errno(status);
+			goto bail;
+		}
+	}
+
 	status = ocfs2_remove_btree_range(inode, &et, trunc_cpos,
 					  phys_cpos, trunc_len, flags, &dealloc,
-					  refcount_loc);
+					  refcount_loc, true);
 	if (status < 0) {
 		mlog_errno(status);
 		goto bail;
@@ -7147,6 +7159,8 @@ int ocfs2_commit_truncate(struct ocfs2_super *osb,
 	goto start;
 
 bail:
+	if (ref_tree)
+		ocfs2_unlock_refcount_tree(osb, ref_tree, 1);
 
 	ocfs2_schedule_truncate_log_flush(osb, 1);
 

fs/ocfs2/alloc.h

@@ -142,7 +142,7 @@ int ocfs2_remove_btree_range(struct inode *inode,
 			     struct ocfs2_extent_tree *et,
 			     u32 cpos, u32 phys_cpos, u32 len, int flags,
 			     struct ocfs2_cached_dealloc_ctxt *dealloc,
-			     u64 refcount_loc);
+			     u64 refcount_loc, bool refcount_tree_locked);
 
 int ocfs2_num_free_extents(struct ocfs2_super *osb,
 			   struct ocfs2_extent_tree *et);

fs/ocfs2/dir.c

@@ -4479,7 +4479,7 @@ int ocfs2_dx_dir_truncate(struct inode *dir, struct buffer_head *di_bh)
 		p_cpos = ocfs2_blocks_to_clusters(dir->i_sb, blkno);
 
 		ret = ocfs2_remove_btree_range(dir, &et, cpos, p_cpos, clen, 0,
-					       &dealloc, 0);
+					       &dealloc, 0, false);
 		if (ret) {
 			mlog_errno(ret);
 			goto out;

fs/ocfs2/file.c

@@ -1803,7 +1803,7 @@ static int ocfs2_remove_inode_range(struct inode *inode,
 
 		ret = ocfs2_remove_btree_range(inode, &et, trunc_cpos,
 					       phys_cpos, trunc_len, flags,
-					       &dealloc, refcount_loc);
+					       &dealloc, refcount_loc, false);
 		if (ret < 0) {
 			mlog_errno(ret);
 			goto out;