linux-kernel - Re: [PATCH 17/33] aio: change reqs_active to include unreaped completions

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Message-ID: <20130402025350.GF30122@thunk.org>
Date:	Mon, 1 Apr 2013 22:53:50 -0400
From:	Theodore Ts'o <tytso@....edu>
To:	Kent Overstreet <koverstreet@...gle.com>
Cc:	linux-kernel@...r.kernel.org, linux-aio@...ck.org,
	akpm@...ux-foundation.org, Zach Brown <zab@...hat.com>,
	Felipe Balbi <balbi@...com>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Mark Fasheh <mfasheh@...e.com>,
	Joel Becker <jlbec@...lplan.org>,
	Rusty Russell <rusty@...tcorp.com.au>,
	Jens Axboe <axboe@...nel.dk>,
	Asai Thambi S P <asamymuthupa@...ron.com>,
	Selvan Mani <smani@...ron.com>,
	Sam Bradshaw <sbradshaw@...ron.com>,
	Jeff Moyer <jmoyer@...hat.com>,
	Al Viro <viro@...iv.linux.org.uk>,
	Benjamin LaHaise <bcrl@...ck.org>
Subject: Re: [PATCH 17/33] aio: change reqs_active to include unreaped
 completions

On Thu, Mar 21, 2013 at 09:35:38AM -0700, Kent Overstreet wrote:
> The aio code tries really hard to avoid having to deal with the completion
> ringbuffer overflowing.  To do that, it has to keep track of the number of
> outstanding kiocbs, and the number of completions currently in the
> ringbuffer - and it's got to check that every time we allocate a kiocb.
> Ouch.
> 
> But - we can improve this quite a bit if we just change reqs_active to
> mean "number of outstanding requests and unreaped completions" - that
> means kiocb allocation doesn't have to look at the ringbuffer, which is a
> fairly significant win.

Signed-off-by: "Theodore Ts'o" <tytso@....edu>

Could you please add a quick comment documenting the reqs_active field
in the struct kioctx definition here?  For future code
maintainability, it should be documented in fs/aio.c, not just in a
commit description.

>  struct kioctx {
>  	atomic_t		users;
>  	atomic_t		dead;
> @@ -92,7 +86,13 @@ struct kioctx {
>  	atomic_t		reqs_active;
>  	struct list_head	active_reqs;	/* used for cancellation */

	       					   - Ted
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