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

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Jens Axboe <axboe@xxxxxxxxx> 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.  ;-)

> 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.

>> The speedups are pretty impressive!
>
> That's why I put them in there, maybe that'd get peoples attention :-)

Indeed.  :)

Cheers,
Jeff



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