From: Nikita Danilov <nikita@clusterfs.com>
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Date: Tue, 6 Dec 2005 20:55:13 +0300
To: Wu Fengguang <wfg@mail.ustc.edu.cn>
Cc: Andrew Morton <akpm@osdl.org>,
       Linux Kernel Mailing List <Linux-Kernel@vger.kernel.org>
Subject: Re: [PATCH 01/16] mm: delayed page activation
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Wu Fengguang writes:
 > On Sun, Dec 04, 2005 at 06:03:15PM +0300, Nikita Danilov wrote:
 > >  > inter-reference distance, and therefore should be better protected(if ignore
 > >  > possible read-ahead effects). If we move re-accessed pages immediately into
 > >  > active_list, we are pushing them closer to danger of eviction.
 > > 
 > > Huh? Pages in the active list are closer to the eviction? If it is
 > > really so, then CLOCK-pro hijacks the meaning of active list in a very
 > > unintuitive way. In the current MM active list is supposed to contain
 > > hot pages that will be evicted last.
 > 
 > The page is going to active list anyway. So its remaining lifetime in inactive
 > list is killed by the early move.

But this change increased lifetimes of _all_ pages, so this is
irrelevant. Consequently, it has a chance of increasing scanning
activity, because there will be more referenced pages at the cold tail
of the inactive list.

And --again-- this erases information about relative order of
references, and this is important. In the past, several VM modifications
(like split inactive_clean and inactive_dirty lists) were tried that had
various advantages over current scanner, but maintained weaker LRU, and
they all were found to degrade horribly under certain easy triggerable
conditions.

 > 
 > Thanks,
 > Wu

Nikita.
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