Stories for 2009-10-09

use Perl Daily Newsletter

In this issue:
    * Measuring copy-on-write on Linux
    * Measuring copy-on-write on Linux

+--------------------------------------------------------------------+
| Measuring copy-on-write on Linux                                   |
|   posted by AndyArmstrong on Thursday October 08, @15:23 (User Jour|
|   http://use.perl.org/article.pl?sid=09/10/08/193244               |
+--------------------------------------------------------------------+

[0]http://perlmonks.org/?node=Corion asked about measuring memory
allocation in IRC but I was reminded of something I've poked at recently
which is measuring how much memory is copy-on-write shared between forked
mod_perl processes. Thus far, when on Linux the only answer I know of is
to use the exmap kernel module. The main page is
[1]http://www.berthels.co.uk/exmap/ but Dave Olszewski wrote some bug
fixes for it at [2]http://github.com/cxreg/exmap. exmap uses a kernel
module to add a new /proc/exmap file. To read physical page stats, write
the PID to this file, then read the results. The exmap distribution comes
with a C++ and perl GTK program to interpret the kernel data. Below is
what I know of the format for the kernel data.

To use:

  $ echo $pid > /proc/exmap
  $ cat /proc/exmap
  VMA 400000 87
  1 0 1c6e7
  1 0 1c6e8
  1 0 1d328
  ...

  $ grep 400000 /proc/$pid/maps
  00400000-00457000 r-xp 00000000 08:01 722755 /usr/bin/screen

The sections provided by /proc/exmap correspond to each of the chunks in
/proc/$pid/maps. Each line then details a page, whether it is swapped,
and whether it is writable.

  (
  VMA $address $page_count
  ( $resident $writable $page_id )+
  )+

Anyway, just thought I'd share. If you know a better trick, I'd love to
hear of it. When I next get around to improving my search servers I'll
likely actually try to use this but for now this is just a tool I think I
plan to use but haven't done serious work with yet.

Discuss this story at:
    http://use.perl.org/comments.pl?sid=09/10/08/193244

Links:
    0. http://perlmonks.org/?node=Corion
    1. http://www.berthels.co.uk/exmap/
    2. http://github.com/cxreg/exmap


+--------------------------------------------------------------------+
| Measuring copy-on-write on Linux                                   |
|   posted by AndyArmstrong on Thursday October 08, @15:26 (Index)   |
|   http://use.perl.org/article.pl?sid=09/10/08/196225               |
+--------------------------------------------------------------------+

[0]http://perlmonks.org/?node=Corion asked about measuring memory
allocation in IRC but I was reminded of something I've poked at recently
which is measuring how much memory is copy-on-write shared between forked
mod_perl processes. Thus far, when on Linux the only answer I know of is
to use the exmap kernel module. The main page is
[1]http://www.berthels.co.uk/exmap/ but Dave Olszewski wrote some bug
fixes for it at [2]http://github.com/cxreg/exmap. exmap uses a kernel
module to add a new /proc/exmap file. To read physical page stats, write
the PID to this file, then read the results. The exmap distribution comes
with a C++ and perl GTK program to interpret the kernel data. Below is
what I know of the format for the kernel data.

To use:

  $ echo $pid > /proc/exmap
  $ cat /proc/exmap
  VMA 400000 87
  1 0 1c6e7
  1 0 1c6e8
  1 0 1d328
  ...

  $ grep 400000 /proc/$pid/maps
  00400000-00457000 r-xp 00000000 08:01 722755 /usr/bin/screen

The sections provided by /proc/exmap correspond to each of the chunks in
/proc/$pid/maps. Each line then details a page, whether it is swapped,
and whether it is writable.

  (
  VMA $address $page_count
  ( $resident $writable $page_id )+
  )+

Anyway, just thought I'd share. If you know a better trick, I'd love to
hear of it. When I next get around to improving my search servers I'll
likely actually try to use this but for now this is just a tool I think I
plan to use but haven't done serious work with yet.

Discuss this story at:
    http://use.perl.org/comments.pl?sid=09/10/08/196225

Links:
    0. http://perlmonks.org/?node=Corion
    1. http://www.berthels.co.uk/exmap/
    2. http://github.com/cxreg/exmap



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