linux-kernel - Re: larger default page sizes...

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Message-ID: <47EA727B.8090606@zytor.com>
Date:	Wed, 26 Mar 2008 08:57:47 -0700
From:	"H. Peter Anvin" <hpa@...or.com>
To:	"J.C. Pizarro" <jcpiza@...il.com>
CC:	David Miller <davem@...emloft.net>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: larger default page sizes...

J.C. Pizarro wrote:
> 
> But there is a general problem of larger pages in systems that
> don't support them natively (in hardware) depending in how it's
> implemented the memory manager in the kernel:
> 
>    "Doubling the soft page size implies
>       halfing the TLB soft-entries in the old hardware".
> 
>    "x4 soft page size=> 1/4 TLB soft-entries, ... and so on."
> 
> Assuming one soft double-sized page represents 2 real-sized pages,
> one replacing of one soft double-sized page implies replacing
> 2 TLB's entries containing the 2 real-sized pages.
> 
> The TLB is very small, its entries are around 24 entries aprox. in
> some processors!.
> 

That's not a problem, actually, since the TLB entries can get shuffled 
like any other (for software TLBs it's a little different, but it can be 
dealt with there too.)

The *real* problem is ABI breakage.

	-hpa
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