From: Pavel Begunkov <asml.silence@gmail.com>
To: Jens Axboe <axboe@kernel.dk>,
linux-block@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH 0/2][for-next] cleanup submission path
Date: Sun, 27 Oct 2019 20:37:13 +0300 [thread overview]
Message-ID: <2ab7134b-2f09-55af-b808-bb6f1285ce16@gmail.com> (raw)
In-Reply-To: <02a25d12-1f44-de18-f233-b5421c608469@kernel.dk>
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On 27/10/2019 20:26, Jens Axboe wrote:
> On 10/27/19 11:19 AM, Pavel Begunkov wrote:
>> On 27/10/2019 19:56, Jens Axboe wrote:
>>> 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.
>>>
>> That's what my question to the fix was about :)
>> 1. Then, what the case it could fail?
>> 2. Is it ok to hold it while polling? It could keep it for quite
>> a long time if host is swift, e.g. submit->poll->submit->poll-> ...
>>
>> Anyway, I will add it back and resend the patchset.
>
> If possible in a simple way, I'd prefer if we do it as a prep patch and
> then queue that up for 5.4 since we now lost that optimization. Then
> layer the other 2 on top of that, since I'll just rebase the 5.5 stuff
> on top of that.
Sure, will do this way. There won't be much difference.
>
> If not trivially possible for 5.4, then we'll just have to leave with it
> in that release. For that case, you can fold the change in with these
> two patches.
>
--
Yours sincerely,
Pavel Begunkov
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next prev parent reply other threads:[~2019-10-27 17:37 UTC|newest]
Thread overview: 17+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-10-27 15:35 [PATCH 0/2][for-next] cleanup submission path Pavel Begunkov
2019-10-27 15:35 ` [PATCH 1/2] io_uring: handle mm_fault outside of submission Pavel Begunkov
2019-10-27 15:35 ` [PATCH 2/2] io_uring: merge io_submit_sqes and io_ring_submit Pavel Begunkov
2019-10-27 16:32 ` [PATCH 0/2][for-next] cleanup submission path Jens Axboe
2019-10-27 16:44 ` Pavel Begunkov
2019-10-27 16:49 ` Jens Axboe
2019-10-27 16:56 ` Jens Axboe
2019-10-27 17:19 ` Pavel Begunkov
2019-10-27 17:26 ` Jens Axboe
2019-10-27 17:37 ` Pavel Begunkov [this message]
2019-10-27 18:56 ` Pavel Begunkov
2019-10-27 19:02 ` Jens Axboe
2019-10-27 19:17 ` Pavel Begunkov
2019-10-27 19:51 ` Jens Axboe
2019-10-27 19:59 ` Pavel Begunkov
2019-10-28 3:38 ` Jens Axboe
2019-10-28 11:12 ` Pavel Begunkov
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