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SubjectRe: [PATCH 4/4] maps: /proc/<pid>/pmaps interface - memory maps in granularity of pages
On Sat, Aug 18, 2007 at 04:45:31PM +0800, Fengguang Wu wrote:
> Matt,
>
> On Sat, Aug 18, 2007 at 01:40:42AM -0500, Matt Mackall wrote:
> > > - On memory pressure,
> > > - as VSZ goes up, RSS will be bounded by physical memory.
> > > So VSZ:RSS ratio actually goes up with memory pressure.
> >
> > And yes.
> >
> > But that's not what I'm talking about. You're likely to have more
> > holes in your ranges with memory pressure as things that aren't active
> > get paged or swapped out and back in. And because we're walking the
> > LRU more rapidly, we'll flip over a lot of the active bits more often
> > which will mean more output.
> >
> > > - page range is a good unit of locality. They are more likely to be
> > > reclaimed as a whole. So (RSS:page_ranges) wouldn't degrade as much.
> >
> > There is that. The relative magnitude of the different effects is
> > unclear. But it is clear that the worst case for pmap is much worse
>
> > than pagemap (two lines per page of RSS?).
> It's one line per page. No sane app will make vmas proliferate.

Sane apps are few and far between.

> So let's talk about the worst case.
>
> pagemap's data set size is determined by VSZ.
> 4GB VSZ means 1M PFNs, hence 8MB pagemap data.
>
> pmaps's data set size is bounded by RSS hence physical memory.
> 4GB RSS means up to 1M page ranges, hence ~20M pmaps data.
> Not too bad :)

Hmmm, I've been misreading the output.

What does it do with nonlinear VMAs?

--
Mathematics is the supreme nostalgia of our time.
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