linux-kernel - Re: [PATCH] block: don't ignore REQ

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Message-ID: <f94b2905-7356-ca9e-6669-ffb98ae3be19@gmail.com>
Date:   Fri, 2 Apr 2021 15:24:11 +0100
From:   Pavel Begunkov <asml.silence@...il.com>
To:     Jens Axboe <axboe@...nel.dk>, linux-block@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] block: don't ignore REQ_NOWAIT for direct IO

On 20/11/2020 19:13, Jens Axboe wrote:
> On 11/20/20 10:10 AM, Pavel Begunkov wrote:
>> io_uring's direct nowait requests end up waiting on io_schedule() in
>> sbitmap, that's seems to be so because blkdev_direct_IO() fails to
>> propagate IOCB_NOWAIT to a bio and hence to blk-mq.
>>
>> Signed-off-by: Pavel Begunkov <asml.silence@...il.com>
>> ---
>>  fs/block_dev.c | 4 ++++
>>  1 file changed, 4 insertions(+)
>>
>> diff --git a/fs/block_dev.c b/fs/block_dev.c
>> index 9e84b1928b94..e7e860c78d93 100644
>> --- a/fs/block_dev.c
>> +++ b/fs/block_dev.c
>> @@ -263,6 +263,8 @@ __blkdev_direct_IO_simple(struct kiocb *iocb, struct iov_iter *iter,
>>  		bio.bi_opf = dio_bio_write_op(iocb);
>>  		task_io_account_write(ret);
>>  	}
>> +	if (iocb->ki_flags & IOCB_NOWAIT)
>> +		bio.bi_opf |= REQ_NOWAIT;
>>  	if (iocb->ki_flags & IOCB_HIPRI)
>>  		bio_set_polled(&bio, iocb);
> 
> Was thinking this wasn't needed, but I guess that users could do sync && NOWAIT
> and get -EAGAIN if using preadv2/pwritev2.
> 
>> @@ -416,6 +418,8 @@ __blkdev_direct_IO(struct kiocb *iocb, struct iov_iter *iter, int nr_pages)
>>  			bio->bi_opf = dio_bio_write_op(iocb);
>>  			task_io_account_write(bio->bi_iter.bi_size);
>>  		}
>> +		if (iocb->ki_flags & IOCB_NOWAIT)
>> +			bio->bi_opf |= REQ_NOWAIT;
>>  
>>  		dio->size += bio->bi_iter.bi_size;
>>  		pos += bio->bi_iter.bi_size;
> 
> Looks fine to me, we definitely should not be waiting on tags for IOCB_NOWAIT
> IO. Will run some shakedown and test for 5.11.
> 

up

-- 
Pavel Begunkov