Jens Axboe <axboe@xxxxxxxxx> writes:
>>>>>>> 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).
...
>>> 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?
>>
>> Yeah, the default is 64k here. We should probably up that. I'd say we
>> either tackle the ridiculously low rlimits, or I guess we just go the
>> aio route and add a sysctl. :-\ I'll see what's involved in the
>> former.
>
> After giving it a bit of thought, let's go the rlimit route. It is cleaner,
> and I don't want a sysctl knob for this either. 64k will enable anyone to
> set up at least one decently sized ring.
OK. Note that the MLOCK_LIMIT size has been dictated by gpg's
requirements:
commit f947ff8af30f75cb9cf0e966caf8f4809ad1b92e
Author: Rik van Riel <riel@xxxxxxxxxx>
Date: Sun Aug 22 23:06:58 2004 -0700
[PATCH] increase per-user mlock limit default to 32k
Since various gnupg users have indicated that gpg wants to mlock 32kB of
memory, I created the patch below that increases the default mlock ulimit
to 32kB.
and then
commit 0833422274ff00729a603b020fac297e69a03e40
Author: Kurt Garloff <garloff@xxxxxxx>
Date: Wed Oct 29 14:00:48 2008 -0700
mm: increase the default mlock limit from 32k to 64k
...
However, newer gpg2 needs 64k in various circumstances and otherwise
fails miserably, see bnc#329675.
So all we need to do is modify gpg2 so that is requires more locked
memory, and we're golden! ;-)
-Jeff
