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-rw-r--r--block/blk-flush.c16
-rw-r--r--block/blk.h21
-rw-r--r--include/linux/blkdev.h1
3 files changed, 32 insertions, 6 deletions
diff --git a/block/blk-flush.c b/block/blk-flush.c
index 6c9b5e1..bb21e4c 100644
--- a/block/blk-flush.c
+++ b/block/blk-flush.c
@@ -212,13 +212,19 @@ static void flush_end_io(struct request *flush_rq, int error)
}
/*
- * Moving a request silently to empty queue_head may stall the
- * queue. Kick the queue in those cases. This function is called
- * from request completion path and calling directly into
- * request_fn may confuse the driver. Always use kblockd.
+ * Kick the queue to avoid stall for two cases:
+ * 1. Moving a request silently to empty queue_head may stall the
+ * queue.
+ * 2. When flush request is running in non-queueable queue, the
+ * queue is hold. Restart the queue after flush request is finished
+ * to avoid stall.
+ * This function is called from request completion path and calling
+ * directly into request_fn may confuse the driver. Always use
+ * kblockd.
*/
- if (queued)
+ if (queued || q->flush_queue_delayed)
blk_run_queue_async(q);
+ q->flush_queue_delayed = 0;
}
/**
diff --git a/block/blk.h b/block/blk.h
index c9df8fc..83e4bff 100644
--- a/block/blk.h
+++ b/block/blk.h
@@ -62,7 +62,26 @@ static inline struct request *__elv_next_request(struct request_queue *q)
rq = list_entry_rq(q->queue_head.next);
return rq;
}
-
+ /*
+ * Flush request is running and flush request isn't queueable
+ * in the drive, we can hold the queue till flush request is
+ * finished. Even we don't do this, driver can't dispatch next
+ * requests and will requeue them. And this can improve
+ * throughput too. For example, we have request flush1, write1,
+ * flush 2. flush1 is dispatched, then queue is hold, write1
+ * isn't inserted to queue. After flush1 is finished, flush2
+ * will be dispatched. Since disk cache is already clean,
+ * flush2 will be finished very soon, so looks like flush2 is
+ * folded to flush1.
+ * Since the queue is hold, a flag is set to indicate the queue
+ * should be restarted later. Please see flush_end_io() for
+ * details.
+ */
+ if (q->flush_pending_idx != q->flush_running_idx &&
+ !queue_flush_queueable(q)) {
+ q->flush_queue_delayed = 1;
+ return NULL;
+ }
if (!q->elevator->ops->elevator_dispatch_fn(q, 0))
return NULL;
}
diff --git a/include/linux/blkdev.h b/include/linux/blkdev.h
index 8bd2a27..9f921bf 100644
--- a/include/linux/blkdev.h
+++ b/include/linux/blkdev.h
@@ -365,6 +365,7 @@ struct request_queue
*/
unsigned int flush_flags;
unsigned int flush_not_queueable:1;
+ unsigned int flush_queue_delayed:1;
unsigned int flush_pending_idx:1;
unsigned int flush_running_idx:1;
unsigned long flush_pending_since;
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