Hi all,
I was recently fooling with /proc for a school project and found out
that ps and top are not doing the same calculation about memory load.
For instance :
ps aux | grep X
3323 1.5 5.9 64948 53996
ok, so the value for the VSS size read by ps is : 64948 and the value
for the RSS size is 53996
Let's look at top now :
PID USER PR NI VIRT RES SHR S %CPU %MEM TIME+ COMMAND
3323 root 15 0 191m 52m 7284 S 11.9 6.0 39:05.93 X
Ok, so for Top , the Virtual mem size is 191m.
This is somewhat different to the 64948Kb found by Ps.
Am I wrong by thinking that these two values should be the same ?
I've done the same test with other programs and most of the times, the
values are the same.
I really don't understand it ;)
I digged a bit deeper to see where the difference comes from.
There are at least two different files in /proc that gives you the mem
load of a particular process.
Those files are : /proc/[PID]/statm and /proc/[PID]/status
let's look at those files for this example
serty2@serty2 ~ $ more /proc/3323/status
Name: X
State: S (sleeping)
SleepAVG: 98%
Tgid: 3323
Pid: 3323
PPid: 3320
TracerPid: 0
Uid: 0 0 0 0
Gid: 0 0 0 0
FDSize: 256
Groups:
VmSize: 65080 kB
VmLck: 0 kB
VmRSS: 54128 kB
VmData: 46772 kB
VmStk: 84 kB
VmExe: 1532 kB
VmLib: 13124 kB
VmPTE: 224 kB
Threads: 1
SigPnd: 0000000000000000
ShdPnd: 0000000000000000
SigBlk: 0000000000000000
SigIgn: 0000000000001000
SigCgt: 00000001d1806ecb
CapInh: 00000000fffffeff
CapPrm: 00000000fffffeff
CapEff: 00000000fffffeff
Ok , so the VmSize is 65080 , that really looks like the value we got
from ps ;)
(not the exact same because of the time delay between the two tests)
Let's look at the other file :
serty2@serty2 ~ $ more /proc/3323/statm
49166 13532 1821 383 0 11714 0
as stated in proc's man , the first value is the total program size in
mem pages.
then : (49166 * 4096) / (1024²) =192Mb
We're pretty close to the value given by Top .
I don't understand why there is a difference for those values for some
programs.
And most important of it, I really don't know what value to use ;)
I think I would go for the value in /proc/[PID]/statm because the
/proc/[PID]/status is supposed to be only a aggregate of information
found in other files and made "human-readable".
But then, I'm not sure.
Does anyone know which file holds the right value ?
Thanks for any comments
Damien
PS : please excuse my english mistakes ;)
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