linux-kernel - Re: [PATCH 2/2] Optimize compound_head() by avoiding a shared page flag

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Message-ID: <Pine.LNX.4.64.0704091020310.4878@schroedinger.engr.sgi.com>
Date:	Mon, 9 Apr 2007 10:22:24 -0700 (PDT)
From:	Christoph Lameter <clameter@....com>
To:	Andrew Morton <akpm@...ux-foundation.org>
cc:	Hugh Dickins <hugh@...itas.com>, Nick Piggin <npiggin@...e.de>,
	dgc@....com, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/2] Optimize compound_head() by avoiding a shared page
 flag

On Sat, 7 Apr 2007, Andrew Morton wrote:

>         andl    $48, %eax       #, tmp399
>         cmpl    $48, %eax       #, tmp399
>         je      .L265   #,
> 
> what's "yuck" about that?


> 
> With the single page flag:
> 
> 	movl	(%ebx), %eax	#* page.521, D.21940
> 	testb	$32, %al	#, D.21940
> 	jne	.L265	#,
> 
> So you're talking about saving one sole single silly solitary instruction.

We are also using another register. The bit instructions can just go in an 
test. Ok. Will submit this patch. .... Maybe I can special case 64 bit.

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