1 files changed, 26 insertions, 4 deletions

diff --git a/fs/fs-writeback.c b/fs/fs-writeback.c
index 24489126f8ca..091a36444972 100644
--- a/fs/fs-writeback.c
+++ b/fs/fs-writeback.c
@@ -1380,6 +1380,10 @@ static long writeback_chunk_size(struct bdi_writeback *wb,
  * Write a portion of b_io inodes which belong to @sb.
  *
  * Return the number of pages and/or inodes written.
+ *
+ * NOTE! This is called with wb->list_lock held, and will
+ * unlock and relock that for each inode it ends up doing
+ * IO for.
  */
 static long writeback_sb_inodes(struct super_block *sb,
                                 struct bdi_writeback *wb,
@@ -1398,9 +1402,7 @@ static long writeback_sb_inodes(struct super_block *sb,
         unsigned long start_time = jiffies;
         long write_chunk;
         long wrote = 0;  /* count both pages and inodes */
-        struct blk_plug plug;
 
-        blk_start_plug(&plug);
         while (!list_empty(&wb->b_io)) {
                 struct inode *inode = wb_inode(wb->b_io.prev);
 
@@ -1479,6 +1481,21 @@ static long writeback_sb_inodes(struct super_block *sb,
                 wbc_detach_inode(&wbc);
                 work->nr_pages -= write_chunk - wbc.nr_to_write;
                 wrote += write_chunk - wbc.nr_to_write;
+
+                if (need_resched()) {
+                        /*
+                         * We're trying to balance between building up a nice
+                         * long list of IOs to improve our merge rate, and
+                         * getting those IOs out quickly for anyone throttling
+                         * in balance_dirty_pages().  cond_resched() doesn't
+                         * unplug, so get our IOs out the door before we
+                         * give up the CPU.
+                         */
+                        blk_flush_plug(current);
+                        cond_resched();
+                }
+
+
                 spin_lock(&wb->list_lock);
                 spin_lock(&inode->i_lock);
                 if (!(inode->i_state & I_DIRTY_ALL))
@@ -1486,7 +1503,7 @@ static long writeback_sb_inodes(struct super_block *sb,
                 requeue_inode(inode, wb, &wbc);
                 inode_sync_complete(inode);
                 spin_unlock(&inode->i_lock);
-                cond_resched_lock(&wb->list_lock);
+
                 /*
                  * bail out to wb_writeback() often enough to check
                  * background threshold and other termination conditions.
@@ -1498,7 +1515,6 @@ static long writeback_sb_inodes(struct super_block *sb,
                                 break;
                 }
         }
-        blk_finish_plug(&plug);
         return wrote;
 }
 
@@ -1545,12 +1561,15 @@ static long writeback_inodes_wb(struct bdi_writeback *wb, long nr_pages,
                 .range_cyclic   = 1,
                 .reason         = reason,
         };
+        struct blk_plug plug;
 
+        blk_start_plug(&plug);
         spin_lock(&wb->list_lock);
         if (list_empty(&wb->b_io))
                 queue_io(wb, &work);
         __writeback_inodes_wb(wb, &work);
         spin_unlock(&wb->list_lock);
+        blk_finish_plug(&plug);
 
         return nr_pages - work.nr_pages;
 }
@@ -1578,10 +1597,12 @@ static long wb_writeback(struct bdi_writeback *wb,
         unsigned long oldest_jif;
         struct inode *inode;
         long progress;
+        struct blk_plug plug;
 
         oldest_jif = jiffies;
         work->older_than_this = &oldest_jif;
 
+        blk_start_plug(&plug);
         spin_lock(&wb->list_lock);
         for (;;) {
                 /*
@@ -1661,6 +1682,7 @@ static long wb_writeback(struct bdi_writeback *wb,
                 }
         }
         spin_unlock(&wb->list_lock);
+        blk_finish_plug(&plug);
 
         return nr_pages - work->nr_pages;
 }