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

[Christian Borntraeger <borntraeger@de.ibm.com>]

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?

Christian