linux-kernel - Re: [PATCH 4/5] aio: vmap ringbuffer

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Message-ID: <20121009225836.GU26187@lenny.home.zabbo.net>
Date:	Tue, 9 Oct 2012 15:58:36 -0700
From:	Zach Brown <zab@...hat.com>
To:	Kent Overstreet <koverstreet@...gle.com>
Cc:	linux-bcache@...r.kernel.org, linux-kernel@...r.kernel.org,
	dm-devel@...hat.com, tytso@....edu
Subject: Re: [PATCH 4/5] aio: vmap ringbuffer

> Not if we decouple the ringbuffer size from max_requests.

Hmm, interesting.

> This would be useful to do anyways because right now, allocating a kiocb
> has to take a global refcount and check head and tail in the ringbuffer
> just so it can avoid overflowing the ringbuffer.

I'm not sure what you mean by a 'global refcount'.. do you mean the
per-mm ctx_lock?

> If we change aio_complete() so that if the ringbuffer is full then the
> kiocb just goes on a linked list - we can size the ringbuffer so this
> doesn't happen normally and avoid the global synchronization in the fast
> path.

How would completion events make their way from the list to the ring if
an app is only checking the ring for completions from userspace?

- z
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