RSS and VSS

[Ganesh Balraman]

Hi All!

What is the difference between RSS and VSS in glance output?

What does they actaully mean?

If particular program is uing more VSS what does it do?

If particular program is using more RSS what does it do?

[DeafFrog · Accepted solution]

Hello Ganesh ,

check this thread :
http://forums11.itrc.hp.com/service/forums/questionanswer.do?threadId=949200

Regards,

[muruganantham raju]

Hi Ganesh,

In simple terms RSS represents the physical memory usage and VSS represents the virtual memory usage.

You can refer the glance metrics help located /opt/perf/paperdocs/gp/C/gp-metrics.txt to get better understanding of these values in glance context. Following are the excerpt from the metrics document.


PROC_MEM_RES
---------------------------------
The size (in KB) of resident memory allocated for the
process(or kernel thread, if HP-UX/Linux Kernel 2.6 and
above).
On HP-UX, the calculation of this metric differs depending on
whether this process has used any CPU time since the midaemon
process was started. This metric is less accurate and does
not include shared memory regions in its calculation when the
process has been idle since the midaemon was started.
On HP-UX, for processes that use CPU time subsequent to
midaemon startup, the resident memory is calculated as

RSS = sum of private region pages +
(sum of shared region pages /
number of references)
The number of references is a count of the number of
attachments to the memory region. Attachments, for shared
regions, may come from several processes sharing the same
memory, a single process with multiple attachments, or
combinations of these.
This value is only updated when a process uses CPU. Thus,
under memory pressure, this value may be higher than the
actual amount of resident memory for processes which are idle
because their memory pages may no longer be resident or the
reference count for shared segments may have changed.
On HP-UX, this metric is specific to a process. If this
metric is reported for a kernel thread, the value for its
associated process is given.
A value of na is displayed when this information is
unobtainable. This information may not be obtainable for
some system (kernel) processes. It may also not be available
for processes.

The size (in KB) of virtual memory allocated for the
process(or kernel thread, if HP-UX/Linux Kernel 2.6 and
above).
On HP-UX, this consists of the sum of the virtual set size of
all private memory regions used by this process, plus this
process share of memory regions which are shared by multiple
processes. For processes that use CPU time, the value is
divided by the reference count for those regions which are
shared.
On HP-UX, this metric is less accurate and does not reflect
the reference count for shared regions for processes that
were started prior to the midaemon process and have not used
any CPU time since the midaemon was started.
On HP-UX, this metric is specific to a process. If this
metric is reported for a kernel thread, the value for its
associated process is given.
On all other Unix systems, this consists of private text,
private data, private stack and shared memory. The reference
count for shared memory is not taken into account, so the
value of this metric represents the total virtual size of all
regions regardless of the number of processes sharing access.
Note also that lazy swap algorithms, sparse address space
malloc calls, and memory-mapped file access can result in
large VSS values. On systems that provide Glance memory
regions detail reports, the drilldown detail per memory
region is useful to understand the nature of memory
allocations for the process.

HTH
Muru

[Ganesh Balraman]

RSS- REAL MEMORY/PHYSICAL MEMEORY

VSS-Virtual Memory/Swap Memory