[ILUG] determining how much memory is shared between multiple processes?

[Justin Mason]

-----BEGIN PGP SIGNED MESSAGE-----
Hash: SHA1


Paul Jakma writes:
> On Sun, 3 Oct 2004, Justin Mason wrote:
> 
> >  t: SHR  --  Shared Mem size (kb)
> >    The amount of shared memory used by a task.  It simply reflects
> >    memory that could be potentially shared with other processes.
> >
> > but some investigation seems to indicate that on my 2.6.6 system, 
> > that *only* applies to code pages loaded from shared libraries; 
> > pages allocated on the heap are never listed in this field, even if 
> > they are unmodified and therefore, presumably, shared.
> 
> Sounds like top simply uses the VmLib value (and probably + VmExe 
> value) from /proc/<pid>/status, used the source? ;)

Can't say I have -- yet ;)

pretty close though -- 

: jm 1313...; top -b -n1 | grep sharetest
23784 jm        16   0 1032 37148  31m 2620    0  0.0  3.6   0:04 sharetest
23788 jm        22   0 1032 37148  31m 2620    0  0.0  3.6   0:02 sharetest

: jm 1258...; sudo cat /proc/23784/status
Name:   sharetest
State:  T (stopped)
SleepAVG:       90%
Tgid:   23784
Pid:    23784
PPid:   3298
TracerPid:      0
Uid:    1000    1000    1000    1000
Gid:    1000    1000    1000    1000
FDSize: 256
Groups: 4 24 25 29 44 105 115 432 1000
VmSize:    37148 kB
VmLck:         0 kB
VmRSS:     32464 kB
VmData:    34512 kB
VmStk:        16 kB
VmExe:       996 kB
VmLib:      1528 kB
Threads:        1
SigPnd: 0000000000000000
ShdPnd: 0000000000000000
SigBlk: 0000000000000000
SigIgn: 0000000000000080
SigCgt: 0000000080000000
CapInh: 0000000000000000
CapPrm: 0000000000000000
CapEff: 0000000000000000

VmStk+VmExe+VmLib = 2540, which is pretty close to 2620.

> > Anyone got any good tips for ways to figure this out?
> 
> I dont think even the kernel knows ;) - well it used not to. With 
> rmap in the kernel, it now probably does, however I dont see any 
> obvious place where that information is exposed..

hmm. wonder if there's an instrumentation module that'd do it...

- --j.
-----BEGIN PGP SIGNATURE-----
Version: GnuPG v1.2.4 (GNU/Linux)
Comment: Exmh CVS

iD8DBQFBYH3UQTcbUG5Y7woRAg9tAKDKuv0j7HvTskdbL/l4IeFMqjThcwCfR6gD
6qykk0DYeGzsu1ICpmSbrZ8=
=hImO
-----END PGP SIGNATURE-----