linux-kernel - Re: [PATCH v2 2/4] blk-flush: split queues for preflush and postflush requests

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Date:   Mon, 31 Jul 2023 22:15:46 +0800
From:   Chengming Zhou <chengming.zhou@...ux.dev>
To:     Christoph Hellwig <hch@....de>
Cc:     axboe@...nel.dk, ming.lei@...hat.com, linux-block@...r.kernel.org,
        linux-kernel@...r.kernel.org, zhouchengming@...edance.com
Subject: Re: [PATCH v2 2/4] blk-flush: split queues for preflush and postflush
 requests

On 2023/7/31 14:15, Christoph Hellwig wrote:
>> -	list_for_each_entry_safe(rq, n, running, queuelist) {
>> +	list_for_each_entry_safe(rq, n, preflush_running, queuelist) {
>> +		unsigned int seq = blk_flush_cur_seq(rq);
>> +
>> +		BUG_ON(seq != REQ_FSEQ_PREFLUSH && seq != REQ_FSEQ_POSTFLUSH);
>> +		blk_flush_complete_seq(rq, fq, seq, error);
>> +	}
>> +
>> +	list_for_each_entry_safe(rq, n, postflush_running, queuelist) {
>>  		unsigned int seq = blk_flush_cur_seq(rq);
>>  
>>  		BUG_ON(seq != REQ_FSEQ_PREFLUSH && seq != REQ_FSEQ_POSTFLUSH);
> 
> Shouldn't the BUG_ON be split into one that only checks for PREFLUSH and
> one only for POSTFLUSH?

Ah yes, will fix it.

> 
>> +	if (fq->flush_pending_idx != fq->flush_running_idx)
>> +		return;
>> +
>> +	if (!list_empty(preflush_pending))
>> +		first_rq = list_first_entry(preflush_pending, struct request, queuelist);
>> +	else if (!list_empty(postflush_pending))
>> +		first_rq = list_first_entry(postflush_pending, struct request, queuelist);
>> +	else
>>  		return;
> 
> Hmm, I don't think both lists can be empty here?

Yes if check fq->flush_pending_since != 0 before.

> 
> I'd simplify this and avoid the overly long lines as:
> 
> 	first_rq = list_first_entry_or_null(preflush_pending, struct request,
> 					    queuelist);
> 	if (!first_rq)
> 		first_rq = list_first_entry_or_null(postflush_pending,
> 						    struct request, queuelist);
> 

This is better, will change it.

Thanks.