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Date: Mon, 1 Apr 2013 22:36:09 -0400
From: "Theodore Ts'o" <tytso@mit.edu>
To: Kent Overstreet <koverstreet@google.com>
Cc: linux-kernel@vger.kernel.org, linux-aio@kvack.org,
        akpm@linux-foundation.org, Zach Brown <zab@redhat.com>,
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        Jeff Moyer <jmoyer@redhat.com>, Al Viro <viro@zeniv.linux.org.uk>,
        Benjamin LaHaise <bcrl@kvack.org>
Subject: Re: [PATCH 16/33] aio: use cancellation list lazily
Message-ID: <20130402023609.GE30122@thunk.org>
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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@mit.edu>

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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