On 1/17/19 1:09 PM, Jens Axboe wrote:
> On 1/17/19 1:03 PM, Jeff Moyer wrote:
>> Jens Axboe <axboe@xxxxxxxxx> writes:
>>
>>> On 1/17/19 5:48 AM, Roman Penyaev wrote:
>>>> On 2019-01-16 18:49, Jens Axboe wrote:
>>>>
>>>> [...]
>>>>
>>>>> +static int io_allocate_scq_urings(struct io_ring_ctx *ctx,
>>>>> + struct io_uring_params *p)
>>>>> +{
>>>>> + struct io_sq_ring *sq_ring;
>>>>> + struct io_cq_ring *cq_ring;
>>>>> + size_t size;
>>>>> + int ret;
>>>>> +
>>>>> + sq_ring = io_mem_alloc(struct_size(sq_ring, array, p->sq_entries));
>>>>
>>>> It seems that sq_entries, cq_entries are not limited at all. Can nasty
>>>> app consume a lot of kernel pages calling io_setup_uring() from a loop
>>>> passing random entries number? (or even better: decreasing entries
>>>> number,
>>>> in order to consume all pages orders with min number of loops).
>>>
>>> Yes, that's an oversight, we should have a limit in place. I'll add that.
>>
>> Can we charge the ring memory to the RLIMIT_MEMLOCK as well? I'd prefer
>> not to repeat the mistake of fs.aio-max-nr.
>
> Sure, we can do that. With the ring limited in size (it's now 4k entries
> at most), the amount of memory gobbled up by that is much smaller than
> the fixed buffers. A max sized ring is about 256k of memory.
One concern here is that, at least looking at my boxes, the default
setting for RLIMIT_MEMLOCK is really low. I'd hate for everyone to run
into issues using io_uring just because it seems to require root,
because the memlock limit is so low.
That's much less of a concern with the fixed buffers, since it's a more
esoteric part of it. But everyone should be able to setup a few io_uring
queues and use them without having to worry about failing due to an
absurdly low RLIMIT_MEMLOCK.
Comments?
--
Jens Axboe
