Re: [PATCH] io_uring: don't mark S_ISBLK async work as unbounded

[Hao Xu <haoxu@linux.alibaba.com>]

在 2021/4/4 下午7:02, Pavel Begunkov 写道:
> On 04/04/2021 11:57, Hao Xu wrote:
>> 在 2021/4/2 下午6:48, Pavel Begunkov 写道:
>>> On 02/04/2021 11:32, Pavel Begunkov wrote:
>>>> On 02/04/2021 09:52, Hao Xu wrote:
>>>>> 在 2021/4/1 下午10:57, Jens Axboe 写道:
>>>>>> S_ISBLK is marked as unbounded work for async preparation, because it
>>>>>> doesn't match S_ISREG. That is incorrect, as any read/write to a block
>>>>>> device is also a bounded operation. Fix it up and ensure that S_ISBLK
>>>>>> isn't marked unbounded.
>>>>>>
>>>>>> Signed-off-by: Jens Axboe <axboe@kernel.dk>
>>>>>>
>>>>> Hi Jens, I saw a (un)bounded work is for a (un)bounded worker to
>>>>> execute. What is the difference between bounded and unbounded?
>>>>
>>>> Unbounded works are not bounded in execution time, i.e. they may take
>>>> forever to complete. E.g. recv depends on the other end to send something,
>>>> that not necessarily will ever happen.
>>>
>>> To elaborate a bit, one example of how it's used: because unbounded may
>>> stay for long, it always spawns a new worker thread for each of them.
>>>
>>> If app submits SQEs as below, and send's are not actually sent for execution
>>> but stashed somewhere internally in a list, e.g. waiting for a worker thread
>>> to get free, it would just hang from the userspace perspective.
>>>
>>> recv(fd1), recv(fd1), send(fd1), send(fd1)
>>>
>> Hi Pavel, thank you for the patient explanation, I got the meaning of
>>   bound/unbond now, but it seems there is no difference handling bounded and unbounded work in the current code?
> 
> It was used in io-wq, so see in io-wq.[c,h] files. Not sure about 5.12+, but
> a quick look shows:
> 
> wqe->acct[IO_WQ_ACCT_BOUND].max_workers = bounded;
> ...
> wqe->acct[IO_WQ_ACCT_UNBOUND].max_workers =
> 			task_rlimit(current, RLIMIT_NPROC);
> 
Thanks, Pavel.:)
> 
> 
>>>>>> diff --git a/fs/io_uring.c b/fs/io_uring.c
>>>>>> index 6d7a1b69712b..a16b7df934d1 100644
>>>>>> --- a/fs/io_uring.c
>>>>>> +++ b/fs/io_uring.c
>>>>>> @@ -1213,7 +1213,7 @@ static void io_prep_async_work(struct io_kiocb *req)
>>>>>>         if (req->flags & REQ_F_ISREG) {
>>>>>>             if (def->hash_reg_file || (ctx->flags & IORING_SETUP_IOPOLL))
>>>>>>                 io_wq_hash_work(&req->work, file_inode(req->file));
>>>>>> -    } else {
>>>>>> +    } else if (!req->file || !S_ISBLK(file_inode(req->file)->i_mode)) {
>>>>>>             if (def->unbound_nonreg_file)
>>>>>>                 req->work.flags |= IO_WQ_WORK_UNBOUND;
>>>>>>         }
>>>
>>
>