Re: scsi-mq V2

[Jens Axboe]

On 2014-07-10 22:05, Jeff Moyer wrote:
> Jens Axboe <axboe@xxxxxxxxx> writes:
>
> > On 2014-07-10 17:11, Jeff Moyer wrote:
> > > Benjamin LaHaise <bcrl@xxxxxxxxx> writes:
> > >
> > > > > [  186.339064] ioctx_alloc: nr_events=-2 aio_max_nr=65536
> > > > > [  186.339065] ioctx_alloc: nr_events=-2 aio_max_nr=65536
> > > > > [  186.339067] ioctx_alloc: nr_events=-2 aio_max_nr=65536
> > > > > [  186.339068] ioctx_alloc: nr_events=-2 aio_max_nr=65536
> > > > > [  186.339069] ioctx_alloc: nr_events=-2 aio_max_nr=65536
> > > >
> > > > Something is horribly wrong here.  There is no way that value for nr_events
> > > > should be passed in to ioctx_alloc().  This implies that userland is calling
> > > > io_setup() with an impossibly large value for nr_events.  Can you post the
> > > > actual diff for your fs/aio.c relative to linus' tree?
> > >
> > > fio does exactly this!  it passes INT_MAX.
> >
> > That's correct, I had actually forgotten about this. It was a change
> > made a few years back, in correlation with the aio optimizations
> > posted then, basically telling aio to ignore that silly (and broken)
> > user ring.
>
> I still don't see how you accomplish that.  Making it bigger doesn't get
> rid of it.  ;-)

See the patches from back then - INT_MAX basically just meant the same 
as 0, but 0 could not be used because of the (silly) setup with the 
wrappers around the syscalls. So INT_MAX was overloaded to mean "no ring 
events, I don't care".

--
Jens Axboe

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