Btrfs: Avoid superfluous tree-log writeout

We allow two log transactions at a time, but use same flag
to mark dirty tree-log btree blocks. So we may flush dirty
blocks belonging to newer log transaction when committing a
log transaction. This patch fixes the issue by using two
flags to mark dirty tree-log btree blocks.

Signed-off-by: Yan Zheng <zheng.yan@oracle.com>
Signed-off-by: Chris Mason <chris.mason@oracle.com>

1 files changed, 10 insertions, 2 deletions

diff --git a/fs/btrfs/extent-tree.c b/fs/btrfs/extent-tree.c
index 94627c4cc193..4a86508ce473 100644
--- a/fs/btrfs/extent-tree.c
+++ b/fs/btrfs/extent-tree.c
@@ -4919,8 +4919,16 @@ struct extent_buffer *btrfs_init_new_buffer(struct btrfs_trans_handle *trans,
         btrfs_set_buffer_uptodate(buf);
 
         if (root->root_key.objectid == BTRFS_TREE_LOG_OBJECTID) {
-                set_extent_dirty(&root->dirty_log_pages, buf->start,
-                         buf->start + buf->len - 1, GFP_NOFS);
+                /*
+                 * we allow two log transactions at a time, use different
+                 * EXENT bit to differentiate dirty pages.
+                 */
+                if (root->log_transid % 2 == 0)
+                        set_extent_dirty(&root->dirty_log_pages, buf->start,
+                                        buf->start + buf->len - 1, GFP_NOFS);
+                else
+                        set_extent_new(&root->dirty_log_pages, buf->start,
+                                        buf->start + buf->len - 1, GFP_NOFS);
         } else {
                 set_extent_dirty(&trans->transaction->dirty_pages, buf->start,
                          buf->start + buf->len - 1, GFP_NOFS);