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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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