Re: [PATCH 8/8] writeback: throttle buffered writeback

[Jens Axboe]

On 04/23/2016 02:21 AM, xiakaixu wrote:
diff --git a/block/blk-core.c b/block/blk-core.c
index 40b57bf4852c..d941f69dfb4b 100644
--- a/block/blk-core.c
+++ b/block/blk-core.c
@@ -39,6 +39,7 @@
  #include "blk.h"
  #include "blk-mq.h"
+#include "blk-wb.h"

  EXPORT_TRACEPOINT_SYMBOL_GPL(block_bio_remap);
  EXPORT_TRACEPOINT_SYMBOL_GPL(block_rq_remap);
@@ -880,6 +881,7 @@ blk_init_allocated_queue(struct request_queue *q, 
request_fn_proc *rfn,

  fail:
        blk_free_flush_queue(q->fq);
+       blk_wb_exit(q);
        return NULL;
  }
  EXPORT_SYMBOL(blk_init_allocated_queue);
@@ -1395,6 +1397,7 @@ void blk_requeue_request(struct request_queue *q, struct 
request *rq)
        blk_delete_timer(rq);
        blk_clear_rq_complete(rq);
        trace_block_rq_requeue(q, rq);
+       blk_wb_requeue(q->rq_wb, rq);

        if (rq->cmd_flags & REQ_QUEUED)
                blk_queue_end_tag(q, rq);
@@ -1485,6 +1488,8 @@ void __blk_put_request(struct request_queue *q, struct 
request *req)
        /* this is a bio leak */
        WARN_ON(req->bio != NULL);

+       blk_wb_done(q->rq_wb, req);
+
        /*
         * Request may not have originated from ll_rw_blk. if not,
         * it didn't come out of our reserved rq pools
@@ -1714,6 +1719,7 @@ static blk_qc_t blk_queue_bio(struct request_queue *q, 
struct bio *bio)
        int el_ret, rw_flags, where = ELEVATOR_INSERT_SORT;
        struct request *req;
        unsigned int request_count = 0;
+       bool wb_acct;

        /*
         * low level driver can indicate that it wants pages above a
@@ -1766,6 +1772,8 @@ static blk_qc_t blk_queue_bio(struct request_queue *q, 
struct bio *bio)
        }

  get_rq:
+       wb_acct = blk_wb_wait(q->rq_wb, bio, q->queue_lock);
+
        /*
         * This sync check and mask will be re-done in init_request_from_bio(),
         * but we need to set it earlier to expose the sync flag to the
@@ -1781,11 +1789,16 @@ get_rq:
         */
        req = get_request(q, rw_flags, bio, GFP_NOIO);
        if (IS_ERR(req)) {
+               if (wb_acct)
+                       __blk_wb_done(q->rq_wb);
                bio->bi_error = PTR_ERR(req);
                bio_endio(bio);
                goto out_unlock;
        }

+       if (wb_acct)
+               req->cmd_flags |= REQ_BUF_INFLIGHT;
+
        /*
         * After dropping the lock and possibly sleeping here, our request
         * may now be mergeable after it had proven unmergeable (above).
@@ -2515,6 +2528,7 @@ void blk_start_request(struct request *req)
        blk_dequeue_request(req);

        req->issue_time = ktime_to_ns(ktime_get());
+       blk_wb_issue(req->q->rq_wb, req);

        /*
         * We are now handing the request to the hardware, initialize
@@ -2751,6 +2765,7 @@ void blk_finish_request(struct request *req, int error)
                blk_unprep_request(req);

        blk_account_io_done(req);
+       blk_wb_done(req->q->rq_wb, req);

Hi Jens,

Seems the function blk_wb_done() will be executed twice even if the end_io
callback is set.
Maybe the same thing would happen in blk-mq.c.

Yeah, that was a mistake, the current version has it fixed. It was 
inadvertently added when I discovered that the flush request didn't work 
properly. Now it just duplicates the call inside the check for if it has 
an ->end_io() defined, since we don't use the normal path for that.

--
Jens Axboe