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

Balbir Singh
2010-06-11T04:46:32Z

* KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com> [2010-06-11 10:54:41]:

> On Thu, 10 Jun 2010 17:07:32 -0700
> Dave Hansen <dave@linux.vnet.ibm.com> wrote:
>
> > 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.
> >
>
> Hmm. I'm not fan of estimating working set size by calculation
> based on some numbers without considering history or feedback.
>
> Can't we use some kind of feedback algorithm as hi-low-watermark, random walk
> or GA (or somehing more smart) to detect the size ?
>

Could you please clarify at what level you are suggesting size
detection? I assume it is outside the OS, right?

--
Three Cheers,
Balbir