[PATCH 0/6] Integrate AIO with wait-bit based filtered wakeups

From: Suparna Bhattacharya
Date: Mon Jun 20 2005 - 10:54:03 EST

On Mon, Jun 20, 2005 at 05:31:54PM +0530, Suparna Bhattacharya wrote:
> Since AIO development is gaining momentum once again, ocfs2 and
> samba both appear to be using AIO, NFS needs async semaphores etc,
> there appears to be an increase in interest in straightening out some
> of the pending work in this area. So this seems like a good
> time to re-post some of those patches for discussion and decision.
> Just to help sync up, here is an initial list based on the pieces
> that have been in progress with patches in existence (please feel free
> to add/update ones I missed or reflected inaccurately here):
> (1) Updating AIO to use wait-bit based filtered wakeups (me/wli)
> Status: Updated to 2.6.12-rc6, needs review

Here is a little bit of background on the motivation behind this set of
patches to update AIO for filtered wakeups:

(a) Since the introduction of filtered wakeups support and
the wait_bit_queue infrastructure in mainline, it is no longer
sufficient to just embed a wait queue entry in the kiocb
for AIO operations involving filtered wakeups.
(b) Given that filesystem reads/writes use filtered wakeups underlying
wait_on_page_bit, fixing this becomes a pre-req for buffered
filesystem AIO.
(c) The wait_bit_queue infrastructure actually enables a cleaner
implementation of filesystem AIO because it already provides
for an action routine intended to allow both blocking and
non-blocking or asynchronous behaviour.

As I was rewriting the patches to address this, there is one other
change I made to resolve one remaining ugliness in my earlier
patchsets - special casing of the form
if (wait == NULL) wait = &local_wait
to switch to a stack based wait queue entry if not passed a wait
queue entry associated with an iocb.

To avoid this, I have tried biting the bullet by including a default
wait bit queue entry in the task structure, to be used instead of
on-demand allocation of a wait bit queue entry on stack.

All in all, these changes have (hopefully) simplified the code,
as well as made it more up-to-date. Comments (including
better names etc as requested by Zach) are welcome !


Suparna Bhattacharya (suparna@xxxxxxxxxx)
Linux Technology Center
IBM Software Lab, India

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