writeback: add comments to bdi_work structure
And document its retriever, get_next_work_item().
Acked-by: Jan Kara <jack@suse.cz>
Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
diff --git a/fs/fs-writeback.c b/fs/fs-writeback.c
index 5887328..55f0d4e 100644
--- a/fs/fs-writeback.c
+++ b/fs/fs-writeback.c
@@ -49,15 +49,15 @@
* Work items for the bdi_writeback threads
*/
struct bdi_work {
- struct list_head list;
- struct rcu_head rcu_head;
+ struct list_head list; /* pending work list */
+ struct rcu_head rcu_head; /* for RCU free/clear of work */
- unsigned long seen;
- atomic_t pending;
+ unsigned long seen; /* threads that have seen this work */
+ atomic_t pending; /* number of threads still to do work */
- struct wb_writeback_args args;
+ struct wb_writeback_args args; /* writeback arguments */
- unsigned long state;
+ unsigned long state; /* flag bits, see WS_* */
};
enum {
@@ -758,7 +758,11 @@
/*
* Return the next bdi_work struct that hasn't been processed by this
- * wb thread yet
+ * wb thread yet. ->seen is initially set for each thread that exists
+ * for this device, when a thread first notices a piece of work it
+ * clears its bit. Depending on writeback type, the thread will notify
+ * completion on either receiving the work (WB_SYNC_NONE) or after
+ * it is done (WB_SYNC_ALL).
*/
static struct bdi_work *get_next_work_item(struct backing_dev_info *bdi,
struct bdi_writeback *wb)