Re: [PATCH 16/33] aio: use cancellation list lazily

[Theodore Ts'o]

On Thu, Mar 21, 2013 at 09:35:37AM -0700, Kent Overstreet wrote:
> Cancelling kiocbs requires adding them to a per kioctx linked list, which
> is one of the few things we need to take the kioctx lock for in the fast
> path.  But most kiocbs can't be cancelled - so if we just do this lazily,
> we can avoid quite a bit of locking overhead.
> 
> While we're at it, instead of using a flag bit switch to using ki_cancel
> itself to indicate that a kiocb has been cancelled/completed.  This lets
> us get rid of ki_flags entirely.


Reviewed-by: "Theodore Ts'o" <tytso@xxxxxxx>

One nit....

> + * And since most things don't implement kiocb cancellation and we'd really like
> + * kiocb completion to be lockless when possible, we use ki_cancel to
> + * synchronize cancellation and completion - we only set it to KIOCB_CANCELLED
> + * with xchg() or cmpxchg(), see batch_complete_aio() and kiocb_cancel().

It's not batch_complete_aio() until later in the patch series.... as
of this commit, it's still aio_complete()

						- Ted
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