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Date: Thu, 7 May 2009 12:32:40 -0400 (EDT)
From: Christoph Lameter <cl@linux.com>
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To: Lee Schermerhorn <Lee.Schermerhorn@hp.com>
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       KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
Subject: Re: [PATCH -mm] vmscan: make mapped executable pages the first class
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On Thu, 7 May 2009, Lee Schermerhorn wrote:

> > Another possibility may be to put the exec pages on the mlock list
> > and scan the list if under extreme duress?
>
> Actually, you don't need to go thru the overhead of mucking with the
> PG_mlocked flag which incurs the rmap walk on unlock, etc.  If one sets
> the the AS_UNEVICTABLE flag, the pages will be shuffled off the the
> unevictable LRU iff we ever try to reclaim them.  And, we do have the
> function to scan the unevictable lru to "rescue" pages in a given
> mapping should we want to bring them back under extreme load.  We'd need
> to remove the AS_UNEVICTABLE flag, first.  This is how
> SHM_LOCK/SHM_UNLOCK works.

We need some way to control this. If there would be a way to simply switch
off eviction of exec pages (via /proc/sys/vm/never_reclaim_exec_pages or
so) I'd use it.