Re: [PATCH 05/15] Add io_uring IO interface

[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

 



On 1/17/19 2:02 PM, Jeff Moyer wrote:
> 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!  ;-)

Haha, that's some nice digging there!

Yes, we could bump it, but with the default, we can get a 512 sized
ring per user, that's 13 pages (rounded up). Probably good enough to
get things off the ground?

-- 
Jens Axboe




[Index of Archives]     [Linux Kernel]     [Kernel Newbies]     [x86 Platform Driver]     [Netdev]     [Linux Wireless]     [Netfilter]     [Bugtraq]     [Linux Filesystems]     [Yosemite Discussion]     [MIPS Linux]     [ARM Linux]     [Linux Security]     [Linux RAID]     [Samba]     [Device Mapper]

  Powered by Linux