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    SubjectRe: [PATCH 4/4] maps: /proc/<pid>/pmaps interface - memory maps in granularity of pages
    On Thu, Aug 16, 2007 at 09:38:46PM -0500, Matt Mackall wrote:
    > On Fri, Aug 17, 2007 at 06:05:20AM +0800, Fengguang Wu wrote:
    > > Show a process's page-by-page address space infomation in /proc/<pid>/pmaps.
    > > It helps to analyze applications' memory footprints in a comprehensive way.
    > >
    > > Pages share the same states are grouped into a page range.
    > > For each page range, the following fields are exported:
    > > - first page index
    > > - number of pages in the range
    > > - well known page/pte flags
    > > - number of mmap users
    > >
    > > Only page flags not expected to disappear in the near future are exported:
    > >
    > > Y:young R:referenced A:active U:uptodate P:ptedirty D:dirty W:writeback
    > ...
    >
    > > The concern of dataset size is taken care of by working in a sparse way:
    > >
    > > 1) It will only generate output for resident pages, that normally is
    > > much smaller than the mapped size. Take my shell for example, the
    > > (size:rss) ratio is (7:1)!
    > >
    > > wfg ~% cat /proc/$$/smaps |grep Size|sum
    > > sum 50552.000
    > > avg 777.723
    > >
    > > wfg ~% cat /proc/$$/smaps |grep Rss|sum
    > > sum 7604.000
    > > avg 116.985
    > >
    > > 2) The page range trick suppresses more output.
    > >
    > > It's interesting to see that the seq_file interface demands some
    > > more programming efforts, and provides such flexibility as well.
    >
    > I'm so-so on this.

    Not that way! It's a good thing that people have different experiences
    and hence viewpoints. Maybe the concept of PFN sharing are
    straightforward to you, while I have been playing with seq_file a lot.

    > On the downside:
    >
    > - requires lots of parsing
    > - isn't random-access
    > - probably significantly slower than pagemap

    That could be true. Maybe some user with huge datasets will give us
    some idea about the performance. I don't know, maybe it's application
    dependent.

    Anyway I don't think it's fair to merge a binary interface without the
    challenge from a textual one ;)

    Thank you,
    Fengguang

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