linux-kernel - Re: [RFC] [PATCH] virtual memmap on sparsemem v3 [0/4] introduction

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Date:	Mon, 11 Dec 2006 09:43:06 +0900
From:	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
To:	"Bob Picco" <bob.picco@...com>
Cc:	linux-kernel@...r.kernel.org, clameter@...r.sgi.com,
	apw@...dowen.org, akpm@...l.org
Subject: Re: [RFC] [PATCH] virtual memmap on sparsemem v3 [0/4] introduction

On Sun, 10 Dec 2006 14:47:30 -0500
"Bob Picco" <bob.picco@...com> wrote:
> > Intro:
> > When using SPARSEMEM, pfn_to_page()/page_to_pfn() accesses global big table
> > of mem_section. if SPARSEMEM_EXTREME, this is 2-level table lookup.
> Did you gather any performance numbers comparing
> VIRTUAL_MEM_MAP+SPARSEMEM to SPARSEMEM+EXTREME? I did some quick but
> inconclusive (small machine) ones when you first posted. There was
> perhaps a slight degradation in VIRTUAL_MEM_MAP+SPARSEMEM.
> 
No, I didn't. I'll do when I have a chance to do it. I hope that this won't
be merged until someone shows the benefit by data.
(I think this verion is better than the first one but..)

IIRC, DISCONTIGMEM + VIRTUAL_MEM_MAP shows a bit better performance than
SPARSEMEM_EXTREME. What I expect is to archive VIRTUAL_MEM_MAP performance
with SPARSEMEM.

Now, we still have chance to optimization.
- optimize pfn_valid. (I'll post this. mem_section[] will be never accessed
  in runtime by this.)
- use large-sized-page (no concrete idea, maybe to modify map/unmap func
  will work enough.)

Thanks,
-Kame

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