linux-kernel - Re: [rfc] increase struct page size?!

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Message-ID: <464FCA28.9040009@cosmosbay.com>
Date:	Sun, 20 May 2007 06:10:16 +0200
From:	Eric Dumazet <dada1@...mosbay.com>
To:	Christoph Lameter <clameter@....com>
CC:	William Lee Irwin III <wli@...omorphy.com>,
	Nick Piggin <npiggin@...e.de>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Linux Memory Management List <linux-mm@...ck.org>,
	linux-arch@...r.kernel.org, Andi Kleen <ak@...e.de>
Subject: Re: [rfc] increase struct page size?!

Christoph Lameter a écrit :
> On Sat, 19 May 2007, William Lee Irwin III wrote:
> 
>> However, there are numerous optimizations and features made possible
>> with flag bits, which might as could be made cheap by padding struct
>> page up to the next highest power of 2 bytes with space for flag bits.
> 
> Well the last time I tried to get this by Andi we became a bit concerned 
> when we realized that the memory map would grow by 14% in size. Given 
> that 4k page size challenged platforms have a huge amount of page structs 
> that growth is significant. I think it would be fine to do it for IA64 
> with 16k page size but not for x86_64.

This reminds me Andi attempted in the past to convert 'flags' to a 32 bits field :

http://marc.info/?l=linux-kernel&m=107903527523739&w=2

I wonder why this idea was not taken, saving 2MB per GB of memory is nice :)

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