writeback: fix WB_SYNC_NONE writeback from umount
When umount calls sync_filesystem(), we first do a WB_SYNC_NONE
writeback to kick off writeback of pending dirty inodes, then follow
that up with a WB_SYNC_ALL to wait for it. Since umount already holds
the sb s_umount mutex, WB_SYNC_NONE ends up doing nothing and all
writeback happens as WB_SYNC_ALL. This can greatly slow down umount,
since WB_SYNC_ALL writeback is a data integrity operation and thus
a bigger hammer than simple WB_SYNC_NONE. For barrier aware file systems
it's a lot slower.
Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
diff --git a/include/linux/writeback.h b/include/linux/writeback.h
index eb38a2c..47e1c68 100644
--- a/include/linux/writeback.h
+++ b/include/linux/writeback.h
@@ -65,6 +65,15 @@
* so we use a single control to update them
*/
unsigned no_nrwrite_index_update:1;
+
+ /*
+ * For WB_SYNC_ALL, the sb must always be pinned. For WB_SYNC_NONE,
+ * the writeback code will pin the sb for the caller. However,
+ * for eg umount, the caller does WB_SYNC_NONE but already has
+ * the sb pinned. If the below is set, caller already has the
+ * sb pinned.
+ */
+ unsigned sb_pinned:1;
};
/*
@@ -73,6 +82,7 @@
struct bdi_writeback;
int inode_wait(void *);
void writeback_inodes_sb(struct super_block *);
+void writeback_inodes_sb_locked(struct super_block *);
int writeback_inodes_sb_if_idle(struct super_block *);
void sync_inodes_sb(struct super_block *);
void writeback_inodes_wbc(struct writeback_control *wbc);