linux-kernel - Re: [PATCH 8/8] writeback: throttle buffered writeback

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Message-ID: <571E024C.2020307@huawei.com>
Date:	Mon, 25 Apr 2016 19:41:00 +0800
From:	xiakaixu <xiakaixu@...wei.com>
To:	Jens Axboe <axboe@...com>
CC:	<linux-kernel@...r.kernel.org>, <linux-fsdevel@...r.kernel.org>,
	<linux-block@...r.kernel.org>, <jack@...e.cz>,
	<dchinner@...hat.com>, "miaoxie (A)" <miaoxie@...wei.com>,
	Bintian <bintian.wang@...wei.com>, Huxinwei <huxinwei@...wei.com>
Subject: Re: [PATCH 8/8] writeback: throttle buffered writeback

于 2016/4/24 5:37, Jens Axboe 写道:
> 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.
>
Hi Jens,

I have checked the wb-buf-throttle branch in your block git repo. I am not sure it is the completed version.
Seems only the problem is fixed in blk-mq.c. The function blk_wb_done() still would be executed twice in blk-core.c.
(the functions blk_finish_request() and __blk_put_request())
Maybe we can add a flag to mark whether blk_wb_done() has been done or not.



-- 
Regards
Kaixu Xia