linux-kernel - Re: [PATCH v2] io_uring/rsrc: fix RLIMIT_MEMLOCK bypass by removing cross-buffer accounting

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Message-ID: <38a46172-8734-462b-870d-39d0697882e1@gmail.com>
Date: Sat, 24 Jan 2026 16:30:25 +0000
From: Pavel Begunkov <asml.silence@...il.com>
To: Jens Axboe <axboe@...nel.dk>, Yuhao Jiang <danisjiang@...il.com>
Cc: io-uring@...r.kernel.org, linux-kernel@...r.kernel.org,
 stable@...r.kernel.org
Subject: Re: [PATCH v2] io_uring/rsrc: fix RLIMIT_MEMLOCK bypass by removing
 cross-buffer accounting

On 1/24/26 15:55, Jens Axboe wrote:
> On 1/24/26 8:14 AM, Jens Axboe wrote:
>>>> ________________________________________________________
>>>> Executed in    2.81 secs    fish           external
>>>>      usr time    0.71 secs  497.00 micros    0.71 secs
>>>>      sys time   19.57 secs  183.00 micros   19.57 secs
>>>>
>>>> which isn't insane. Obviously also needs conditional rescheduling in the
>>>> page loops, as those can take a loooong time for large amounts of
>>>> memory.
>>>
>>> 2.8 sec sounds like a lot as well, makes me wonder which part of
>>> that is mm, but it mm should scale fine-ish. Surely there will be
>>> contention on page refcounts but at least the table walk is
>>> lockless in the best case scenario and otherwise seems to be read
>>> protected by an rw lock.
>>
>> Well a lot of that is also just faulting in the memory on clear, test
>> case should probably be modified to do its own timing. And iterating
>> page arrays is a huge part of it too. There's no real contention in that
>> 2.8 seconds.
> 
> I checked and the faulting part is 2.0s of that runtime. On a re-run:

Makes sense, I was forgetting it's full time.

-- 
Pavel Begunkov