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

Jens Axboe
2026-01-24T15:55:47Z

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:

axboe@r7625 ~> time ./ppage 32 32
register 32 GB, num threads 32
clear msec 2011

________________________________________________________
Executed in 3.13 secs fish external
usr time 0.78 secs 193.00 micros 0.78 secs
sys time 27.46 secs 271.00 micros 27.46 secs

Or just a single thread:

axboe@r7625 ~> time ./ppage 32 1
register 32 GB, num threads 1
clear msec 2081

________________________________________________________
Executed in 2.29 secs fish external
usr time 0.58 secs 750.00 micros 0.58 secs
sys time 1.71 secs 0.00 micros 1.71 secs

axboe@r7625 ~ [1]> time ./ppage 64 1
register 64 GB, num threads 1
clear msec 5380

________________________________________________________
Executed in 6.24 secs fish external
usr time 1.42 secs 328.00 micros 1.42 secs
sys time 4.82 secs 375.00 micros 4.82 secs

--
Jens Axboe