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SubjectRe: scsi-mq V2
On 2014-07-10 22:05, Jeff Moyer wrote:
> Jens Axboe <axboe@kernel.dk> writes:
>
>> On 2014-07-10 17:11, Jeff Moyer wrote:
>>> Benjamin LaHaise <bcrl@kvack.org> 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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