Re: Revert "aio: block exit_aio() until all context requests are completed"

[Jens Axboe <axboe@kernel.dk>]

On 05/15/2015 09:26 AM, Christian Borntraeger wrote:
> Am 15.05.2015 um 15:42 schrieb Jeff Moyer:
>> Christian Borntraeger <borntraeger@de.ibm.com> writes:
>>
>>> I see a significant latency (can be minutes with 2000 disks and HZ=100)
>>> when exiting a QEMU process that has lots of disk devices via aio. The
>>> process sits idle doing nothing as zombie in exit_aio waiting for the
>>> completion.
>>>
>>> Turns out that
>>> commit 6098b45b32 ("aio: block exit_aio() until all context requests are
>>> completed") caused the delay.
>>>
>>> Patch description was:
>>>
>>> It seems that exit_aio() also needs to wait for all iocbs to complete (like
>>> io_destroy), but we missed the wait step in current implemention, so fix
>>> it in the same way as we did in io_destroy.
>>>
>>> Now: io_destroy requires to block until everything is cleaned up from its
>>> interface description in the manpage:
>>> DESCRIPTION
>>> The  io_destroy()  system call will attempt to cancel all outstanding
>>> asynchronous I/O operations against ctx_id, will block on the completion
>>> of all operations that could not be canceled, and will destroy the ctx_id.
>>>
>>> Does process exit require the same full blocking? We might be able to
>>> cleanup the process and let the aio data structures be freed lazily.
>>> Opinions or better ideas?
>>
>> This has already been fixed:
>>
>> commit dc48e56d761610da4ea1088d1bea0a030b8e3e43
>> Author: Jens Axboe <axboe@fb.com>
>> Date:   Wed Apr 15 11:17:23 2015 -0600
>>
>>      aio: fix serial draining in exit_aio()
>>
>> Cheers,
>> Jeff
>>
> Cool thanks. As the original patch had cc stable, shouldnt the fix also be backported?

I'll email stable.

-- 
Jens Axboe