writeback: pass in super_block to bdi_start_writeback()

Sometimes we only want to write pages from a specific super_block,
so allow that to be passed in.

This fixes a problem with commit 56a131dcf7ed36c3c6e36bea448b674ea85ed5bb
causing writeback on all super_blocks on a bdi, where we only really
want to sync a specific sb from writeback_inodes_sb().

Signed-off-by: Jens Axboe <jens.axboe@oracle.com>

3 files changed, 7 insertions, 4 deletions

diff --git a/fs/fs-writeback.c b/fs/fs-writeback.c
index fb61178c86e3..9d5360c4c2af 100644
--- a/fs/fs-writeback.c
+++ b/fs/fs-writeback.c
@@ -250,9 +250,11 @@ static void bdi_sync_writeback(struct backing_dev_info *bdi,
  *   completion. Caller need not hold sb s_umount semaphore.
  *
  */
-void bdi_start_writeback(struct backing_dev_info *bdi, long nr_pages)
+void bdi_start_writeback(struct backing_dev_info *bdi, struct super_block *sb,
+                         long nr_pages)
 {
         struct wb_writeback_args args = {
+                .sb             = sb,
                 .sync_mode      = WB_SYNC_NONE,
                 .nr_pages       = nr_pages,
                 .range_cyclic   = 1,
@@ -1206,7 +1208,7 @@ void writeback_inodes_sb(struct super_block *sb)
         nr_to_write = nr_dirty + nr_unstable +
                         (inodes_stat.nr_inodes - inodes_stat.nr_unused);
 
-        bdi_start_writeback(sb->s_bdi, nr_to_write);
+        bdi_start_writeback(sb->s_bdi, sb, nr_to_write);
 }
 EXPORT_SYMBOL(writeback_inodes_sb);
 
diff --git a/include/linux/backing-dev.h b/include/linux/backing-dev.h
index 0ee33c2e6129..b449e738533a 100644
--- a/include/linux/backing-dev.h
+++ b/include/linux/backing-dev.h
@@ -101,7 +101,8 @@ int bdi_register(struct backing_dev_info *bdi, struct device *parent,
                 const char *fmt, ...);
 int bdi_register_dev(struct backing_dev_info *bdi, dev_t dev);
 void bdi_unregister(struct backing_dev_info *bdi);
-void bdi_start_writeback(struct backing_dev_info *bdi, long nr_pages);
+void bdi_start_writeback(struct backing_dev_info *bdi, struct super_block *sb,
+                                long nr_pages);
 int bdi_writeback_task(struct bdi_writeback *wb);
 int bdi_has_dirty_io(struct backing_dev_info *bdi);
 
diff --git a/mm/page-writeback.c b/mm/page-writeback.c
index 69b5fbabc8bd..a3b14090b1fb 100644
--- a/mm/page-writeback.c
+++ b/mm/page-writeback.c
@@ -596,7 +596,7 @@ static void balance_dirty_pages(struct address_space *mapping,
             (!laptop_mode && ((global_page_state(NR_FILE_DIRTY)
                                + global_page_state(NR_UNSTABLE_NFS))
                                           > background_thresh)))
-                bdi_start_writeback(bdi, 0);
+                bdi_start_writeback(bdi, NULL, 0);
 }
 
 void set_page_dirty_balance(struct page *page, int page_mkwrite)