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

    Regards
    Suparna

    --
    Suparna Bhattacharya (suparna@in.ibm.com)
    Linux Technology Center
    IBM Software Lab, India

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