linux-kernel - Re: [PATCH 01/11] DIO: Separate fields only used in the submission path from struct dio

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Date:	Mon, 08 Aug 2011 13:59:08 -0400
From:	Jeff Moyer <jmoyer@...hat.com>
To:	Andi Kleen <andi@...stfloor.org>
Cc:	linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org,
	hch@...radead.org, Andi Kleen <ak@...ux.intel.com>
Subject: Re: [PATCH 01/11] DIO: Separate fields only used in the submission path from struct dio

Andi Kleen <andi@...stfloor.org> writes:

> From: Andi Kleen <ak@...ux.intel.com>
>
> This large, but largely mechanic, patch moves all fields in struct dio
> that are only used in the submission path into a separate on stack
> data structure. This has the advantage that the memory is very likely
> cache hot, which is not guaranteed for memory fresh out of kmalloc.
>
> This also gives gcc more optimization potential because it can easier
> determine that there are no external aliases for these variables.
>
> The sdio initialization is a initialization now instead of memset.
> This allows gcc to break sdio into individual fields and optimize
> away unnecessary zeroing (after all the functions are inlined)
>
> Signed-off-by: Andi Kleen <ak@...ux.intel.com>

The pages array is only used on submission.  Why did it land in the
struct dio?  I would also think you'd want to keep it close to
curr_page, head, tail.

Cheers,
Jeff
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