Re: "Cannot allocate memory" on ring creation (not RLIMIT_MEMLOCK)

From: Jens Axboe <axboe@kernel.dk>
To: Pavel Begunkov <asml.silence@gmail.com>, Josef <josef.grieb@gmail.com>
Cc: Norman Maurer <norman.maurer@googlemail.com>,
	Dmitry Kadashev <dkadashev@gmail.com>,
	io-uring <io-uring@vger.kernel.org>
Subject: Re: "Cannot allocate memory" on ring creation (not RLIMIT_MEMLOCK)
Date: Sun, 20 Dec 2020 09:14:07 -0700	[thread overview]
Message-ID: <ff816e37-ce0e-79c7-f9bf-9fa94d62484d@kernel.dk> (raw)
In-Reply-To: <0fb27d06-af82-2e1b-f8c5-3a6712162178@gmail.com>

On 12/20/20 6:00 AM, Pavel Begunkov wrote:
> On 20/12/2020 07:13, Josef wrote:
>>> Guys, do you share rings between processes? Explicitly like sending
>>> io_uring fd over a socket, or implicitly e.g. sharing fd tables
>>> (threads), or cloning with copying fd tables (and so taking a ref
>>> to a ring).
>>
>> no in netty we don't share ring between processes
>>
>>> In other words, if you kill all your io_uring applications, does it
>>> go back to normal?
>>
>> no at all, the io-wq worker thread is still running, I literally have
>> to restart the vm to go back to normal(as far as I know is not
>> possible to kill kernel threads right?)
>>
>>> Josef, can you test the patch below instead? Following Jens' idea it
>>> cancels more aggressively when a task is killed or exits. It's based
>>> on [1] but would probably apply fine to for-next.
>>
>> it works, I run several tests with eventfd read op async flag enabled,
>> thanks a lot :) you are awesome guys :)
> 
> Thanks for testing and confirming! Either we forgot something in
> io_ring_ctx_wait_and_kill() and it just can't cancel some requests,
> or we have a dependency that prevents release from happening.

Just a guess - Josef, is the eventfd for the ring fd itself?

BTW, the io_wq_cancel_all() in io_ring_ctx_wait_and_kill() needs to go.
We should just use targeted cancelation - that's cleaner, and the
cancel all will impact ATTACH_WQ as well. Separate thing to fix, though.

-- 
Jens Axboe