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, 20 insertions, 13 deletions

diff --git a/fs/btrfs/tree-log.c b/fs/btrfs/tree-log.c
index 741666a7676a..31da0002e78b 100644
--- a/fs/btrfs/tree-log.c
+++ b/fs/btrfs/tree-log.c
@@ -1977,10 +1977,11 @@ int btrfs_sync_log(struct btrfs_trans_handle *trans,
 {
         int index1;
         int index2;
+        int mark;
         int ret;
         struct btrfs_root *log = root->log_root;
         struct btrfs_root *log_root_tree = root->fs_info->log_root_tree;
-        u64 log_transid = 0;
+        unsigned long log_transid = 0;
 
         mutex_lock(&root->log_mutex);
         index1 = root->log_transid % 2;
@@ -2014,24 +2015,29 @@ int btrfs_sync_log(struct btrfs_trans_handle *trans,
                 goto out;
         }
 
+        log_transid = root->log_transid;
+        if (log_transid % 2 == 0)
+                mark = EXTENT_DIRTY;
+        else
+                mark = EXTENT_NEW;
+
         /* we start IO on  all the marked extents here, but we don't actually
          * wait for them until later.
          */
-        ret = btrfs_write_marked_extents(log, &log->dirty_log_pages);
+        ret = btrfs_write_marked_extents(log, &log->dirty_log_pages, mark);
         BUG_ON(ret);
 
         btrfs_set_root_node(&log->root_item, log->node);
 
         root->log_batch = 0;
-        log_transid = root->log_transid;
         root->log_transid++;
         log->log_transid = root->log_transid;
         root->log_start_pid = 0;
         smp_mb();
         /*
-         * log tree has been flushed to disk, new modifications of
-         * the log will be written to new positions. so it's safe to
-         * allow log writers to go in.
+         * IO has been started, blocks of the log tree have WRITTEN flag set
+         * in their headers. new modifications of the log will be written to
+         * new positions. so it's safe to allow log writers to go in.
          */
         mutex_unlock(&root->log_mutex);
 
@@ -2052,7 +2058,7 @@ int btrfs_sync_log(struct btrfs_trans_handle *trans,
 
         index2 = log_root_tree->log_transid % 2;
         if (atomic_read(&log_root_tree->log_commit[index2])) {
-                btrfs_wait_marked_extents(log, &log->dirty_log_pages);
+                btrfs_wait_marked_extents(log, &log->dirty_log_pages, mark);
                 wait_log_commit(trans, log_root_tree,
                                 log_root_tree->log_transid);
                 mutex_unlock(&log_root_tree->log_mutex);
@@ -2072,16 +2078,17 @@ int btrfs_sync_log(struct btrfs_trans_handle *trans,
          * check the full commit flag again
          */
         if (root->fs_info->last_trans_log_full_commit == trans->transid) {
-                btrfs_wait_marked_extents(log, &log->dirty_log_pages);
+                btrfs_wait_marked_extents(log, &log->dirty_log_pages, mark);
                 mutex_unlock(&log_root_tree->log_mutex);
                 ret = -EAGAIN;
                 goto out_wake_log_root;
         }
 
         ret = btrfs_write_and_wait_marked_extents(log_root_tree,
-                                &log_root_tree->dirty_log_pages);
+                                &log_root_tree->dirty_log_pages,
+                                EXTENT_DIRTY | EXTENT_NEW);
         BUG_ON(ret);
-        btrfs_wait_marked_extents(log, &log->dirty_log_pages);
+        btrfs_wait_marked_extents(log, &log->dirty_log_pages, mark);
 
         btrfs_set_super_log_root(&root->fs_info->super_for_commit,
                                 log_root_tree->node->start);
@@ -2147,12 +2154,12 @@ int btrfs_free_log(struct btrfs_trans_handle *trans, struct btrfs_root *root)
 
         while (1) {
                 ret = find_first_extent_bit(&log->dirty_log_pages,
-                                    0, &start, &end, EXTENT_DIRTY);
+                                0, &start, &end, EXTENT_DIRTY | EXTENT_NEW);
                 if (ret)
                         break;
 
-                clear_extent_dirty(&log->dirty_log_pages,
-                                   start, end, GFP_NOFS);
+                clear_extent_bits(&log->dirty_log_pages, start, end,
+                                  EXTENT_DIRTY | EXTENT_NEW, GFP_NOFS);
         }
 
         if (log->log_transid > 0) {