Re: [PATCH 27/27] aio: add support for pre-mapped user IO buffers

[Jens Axboe <axboe@kernel.dk>]

On 11/30/18 3:04 PM, Jeff Moyer wrote:
> Jens Axboe <axboe@kernel.dk> writes:
> 
>>>> A limit of 4M is imposed as the largest buffer we currently support.
>>>> There's nothing preventing us from going larger, but we need some cap,
>>>> and 4M seemed like it would definitely be big enough.
>>>
>>> Doesn't this mean that a user can pin a bunch of memory?  Something like
>>> 4MB * aio_max_nr?
>>>
>>> $ sysctl fs.aio-max-nr
>>> fs.aio-max-nr = 1048576
>>>
>>> If so, it may be a good idea to account the memory under RLIMIT_MEMLOCK.
>>
>> Yes, it'll need some kind of limiting, right now the limit would indeed
>> be aio-max-nr * 4MB. 4G isn't terrible, but...
> 
> Unless my math's wrong, that's 4TiB on my system.  ;-)

I guess that's a little more terrible ;-)

>> RLIMIT_MEMLOCK isn't a bad idea.
>>
>>> I'm not sure how close you are to proposing this patch set for realz.
>>> If it's soon (now?), then CC-ing linux-api and writing man pages would
>>> be a good idea.  I can help out with the libaio bits if you'd like.  I
>>> haven't yet had time to take this stuff for a spin, sorry.  I'll try to
>>> get to that soonish.
>>
>> I am proposing it for real, not sure how long it'll take to get it
>> reviewed and moved forward. Unless I get lucky. 4.22 seems like a more
>> viable version than 4.21.
>>
>> I'll take any help I can get on the API/man page parts. And/or testing!
> 
> OK, I'll add libaio support (including unit tests), write the man page,
> and I'll definitely do some testing.  I'll start on all that probably in
> the latter half of next week.

Awesome, that's much appreciated!

-- 
Jens Axboe