linux-kernel - Re: [PATCH 0/2][for-next] cleanup submission path

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Date:   Sun, 27 Oct 2019 10:56:46 -0600
From:   Jens Axboe <axboe@...nel.dk>
To:     Pavel Begunkov <asml.silence@...il.com>,
        linux-block@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 0/2][for-next] cleanup submission path

On 10/27/19 10:49 AM, Jens Axboe wrote:
> On 10/27/19 10:44 AM, Pavel Begunkov wrote:
>> On 27/10/2019 19:32, Jens Axboe wrote:
>>> On 10/27/19 9:35 AM, Pavel Begunkov wrote:
>>>> A small cleanup of very similar but diverged io_submit_sqes() and
>>>> io_ring_submit()
>>>>
>>>> Pavel Begunkov (2):
>>>>      io_uring: handle mm_fault outside of submission
>>>>      io_uring: merge io_submit_sqes and io_ring_submit
>>>>
>>>>     fs/io_uring.c | 116 ++++++++++++++------------------------------------
>>>>     1 file changed, 33 insertions(+), 83 deletions(-)
>>>
>>> I like the cleanups here, but one thing that seems off is the
>>> assumption that io_sq_thread() always needs to grab the mm. If
>>> the sqes processed are just READ/WRITE_FIXED, then it never needs
>>> to grab the mm.
>>> Yeah, we removed it to fix bugs. Personally, I think it would be
>> clearer to do lazy grabbing conditionally, rather than have two
>> functions. And in this case it's easier to do after merging.
>>
>> Do you prefer to return it back first?
> 
> Ah I see, no I don't care about that.

OK, looked at the post-patches state. It's still not correct. You are
grabbing the mm from io_sq_thread() unconditionally. We should not do
that, only if the sqes we need to submit need mm context.

-- 
Jens Axboe