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

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Date:	Mon, 22 Jan 2007 18:44:02 -0800 (PST)
From:	Christoph Lameter <clameter@....com>
To:	Rik van Riel <riel@...hat.com>
cc:	Balbir Singh <balbir@...ibm.com>,
	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 Mon, 22 Jan 2007, Rik van Riel wrote:

> The big one is how we are to do some background aging in a
> clock-pro system, so referenced bits don't just pile up when
> the VM has enough memory - otherwise we might not know the
> right pages to evict when a new process starts up and starts
> allocating lots of memory.

There are two bad choices right?

1. Scan for reference bits

   Bad because we may have to scan quite a bit without too much
   result. LRU allows us to defer this until memory is tight.
   Any such scan will pollute the cache and cause a stall of
   the app. You really do not want this for a realtime system.

2. Take faults on reference and update the page state.
   Bad because this means a fault if the reference bit
   has not been set. Could be many faults.

Clock pro really requires 2 right? So lots of additional page faults?
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