Re: aio_down() patch series -- cancellation support added

[Benjamin LaHaise <bcrl@kvack.org>]

On Thu, Jun 23, 2005 at 06:59:26PM +0530, Suparna Bhattacharya wrote:
> One quick question.
> Since lock_kiocb() may block, does that mean that the aio worker thread
> could be put to sleep while an iocb cancellation is in progress, even though
> there may be other iocbs/ioctx's to process ?

It's mostly to deal with the case in the other direction: an iocb that is 
in the process of being cancelled somehow needs to block any retries from 
occurring.  Likewise, if a retry was in progress, the cancellation needs 
to be blocked until that retry is complete.  It should be sufficiently 
rare that it's not a problem, but we may have to revisit the issue as more 
cancel methods get written.

> Looking at the rest a little more closely in terms of how everything
> will fit together, a few questions come to mind - need to think
> about it a little more. I guess the main reason you need the aio_down_wait
> callback is to make sure the semaphore is grabbed right in the context
> of the wakeup rather than at retry time, is that correct ?

Yes, that way the retry method is only called if it will make progress, 
and we will not have a thundering herd problem.  I'm debugging the changes 
needed to implement async pipes using aio_down(), and the patch so far 
looks pretty straightforward.

		-ben
-- 
"Time is what keeps everything from happening all at once." -- John Wheeler