linux-kernel - Re: Why active list and inactive list?

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Message-ID: <Pine.LNX.4.64.0701221923300.30667@schroedinger.engr.sgi.com>
Date:	Mon, 22 Jan 2007 19:28:01 -0800 (PST)
From:	Christoph Lameter <clameter@....com>
To:	Balbir Singh <balbir@...ibm.com>
cc:	Andrea Arcangeli <andrea@...e.de>,
	Niki Hammler <mailinglists@...aq.net>,
	linux-kernel@...r.kernel.org,
	Vaidyanathan Srinivasan <svaidy@...ux.vnet.ibm.com>
Subject: Re: Why active list and inactive list?

On Tue, 23 Jan 2007, Balbir Singh wrote:

> When you unmap or map, you need to touch the pte entries and know the
> pages involved, so shouldn't be equivalent to a list_del and list_add
> for each page impacted by the map/unmap operation?

When you unmap and map you must currently get exclusive access to the 
cachelines of the pte and the cacheline of the page struct. If we use a 
list_move on page->lru then we have would have to update pointers in up 
to 4 other page structs. Thus we need exclusive access to 4 additional 
cachelines. This triples the number of cachelines touched. Instead of 2 
cachelines we need 6.

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