linux-kernel - Re: [PATCH 09/10] Change table chaining layout

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Message-ID: <20071023214442.GL14671@kernel.dk>
Date:	Tue, 23 Oct 2007 23:44:42 +0200
From:	Jens Axboe <jens.axboe@...cle.com>
To:	Andi Kleen <andi@...stfloor.org>
Cc:	Boaz Harrosh <bharrosh@...asas.com>, torvalds@...ux-foundation.org,
	linux-kernel@...r.kernel.org, mingo@...e.hu
Subject: Re: [PATCH 09/10] Change table chaining layout

On Tue, Oct 23 2007, Andi Kleen wrote:
> On Tue, Oct 23, 2007 at 10:20:17PM +0200, Jens Axboe wrote:
> > On Tue, Oct 23 2007, Andi Kleen wrote:
> > > Jens Axboe <jens.axboe@...cle.com> writes:
> > > 
> > > >> You might want to put a BUG_ON(page & 0x3); Make sure
> > > >> you're not loosing information. (The m68k problem)
> > > >
> > > > That's a really good idea, thanks Boaz! I'll add that.
> > > 
> > > It would be even better if you replaced all the magic numbers with defines
> > > or better accessors.
> > 
> > All? There are two numbers, and all are confined to scatterlist.h
> > privately. Except the one in blk_rq_map_sg(), which was done on purpose
> > since I don't want to export that knowledge to others. So we definitely
> > don't want accessors, I can name the two bit values but don't see much
> > point in doing it.
> 
> Maybe no point for you, but it would be helpful for any poor soul
> who has to read/debug/change the code later.

I understand, but if you look in the include file that uses the magic
numbers, then there's a big comment block in the beginning describing
the usage.

> Even if they're limited right now that doesn't mean it'll stay
> that way anyways.

Since it's reusing lower page bits, we can't go beyond 2 bits anyway. So
I'll be surprised if they expand :-)

-- 
Jens Axboe

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