On 1/17/19 1:09 PM, Jens Axboe wrote: > On 1/17/19 1:03 PM, Jeff Moyer wrote: >> Jens Axboe <[email protected]> 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
