Re: [PATCH 2/2] io_uring/memmap: only charge pinned user memory to RLIMIT_MEMLOCK

[Jens Axboe <axboe@kernel.dk>]

On 10/7/26 10:57 PM, Hengyu Liang wrote:
> On 10/7/26 3:38 PM, Jens Axboe wrote:
>> Charge RLIMIT_MEMLOCK only for regions backed by pinned user memory, which
>> is what the limit is for, and leave kernel allocations to memcg. User
>> provided ring memory keeps being charged, it is pinned.
> 
> Sorry for the late reply, and thanks for picking this up.
> 
> I tested both patches on top of v7.3-rc4. The test case from my patch
> prints "64 rings" again, kernel allocated buffer rings are fixed as well,
> the per-user locked_vm count is balanced after ring create, close and
> resize, and the liburing tests give the same results as before, except
> that read-before-exit.t passes again with the default limit.
> 
> Tested-by: Hengyu Liang <hengyul@cs.unc.edu>

Thanks for testing!

> One case is not restored. v6.13 did not charge rings created with
> IORING_SETUP_NO_MMAP either. Number of rings created out of 64, as an
> unprivileged user with the default 8 MiB limit, 4096 entries each:
> 
>                                      v6.13  v7.3-rc4  this series
>   io_uring_queue_init()                 64        16           64
>   io_uring_queue_init_mem()             64        21           21
> 
> PostgreSQL 18 is in the second row. It puts its rings into shared memory
> with io_uring_queue_init_mem() whenever liburing has it [1], so I expect
> the failure they reported to stay. I have not run PostgreSQL itself.
> 
> Would you take a patch on top that leaves the SQ/CQ rings uncharged for
> user memory too, as in v6.13? I can send one, or test whatever you prefer.

Yes for sure, please feel free to send a patch we can apply on top.
>
> Also, kernel allocated IORING_REGISTER_MEM_REGION regions are no longer
> charged. They have been charged since they were added in v6.14. With the
> series a user with an 8 MiB limit can register a 512 MiB one.
> 
> [1] https://github.com/postgres/postgres/blob/REL_18_STABLE/src/backend/storage/aio/method_io_uring.c

We should still account IORING_MEM_REGION_TYPE_USER, anything that isn't
memcg accounted. I'll take a closer look, but if that isn't the case,
then yes that also needs a followup.

-- 
Jens Axboe