Re: [RFC/T/D][PATCH 2/2] Linux/Guest cooperative unmapped pagecache control

From: Dave Hansen
Date: Thu Jun 10 2010 - 21:13:57 EST

On Thu, 2010-06-10 at 19:55 +0530, Balbir Singh wrote:
> > I'm not sure victimizing unmapped cache pages is a good idea.
> > Shouldn't page selection use the LRU for recency information instead
> > of the cost of guest reclaim? Dropping a frequently used unmapped
> > cache page can be more expensive than dropping an unused text page
> > that was loaded as part of some executable's initialization and
> > forgotten.
> We victimize the unmapped cache only if it is unused (in LRU order).
> We don't force the issue too much. We also have free slab cache to go
> after.

Just to be clear, let's say we have a mapped page (say of /sbin/init)
that's been unreferenced since _just_ after the system booted. We also
have an unmapped page cache page of a file often used at runtime, say
one from /etc/resolv.conf or /etc/passwd.

Which page will be preferred for eviction with this patch set?

-- Dave

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