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Hi

Which is the best tool to use for checking how much memory a process uses ?
Ist it ps -efl, glance or top ?
Why don the values for a specific process from these different tools match
?

thanks

Shaun

shaun.lukhan@eskom.co.za wrote:
|Hi

|Which is the best tool to use for checking how much memory a process uses ?
|Ist it ps -efl, glance or top ?
|Why don the values for a specific process from these different tools match
|?

Glance is the best tool, as it gives the most complete information.
The various tools report different numbers because they disagree about
which regions to report as part of the size and how to count shared memory
regions.

When looking at that size of a process, there really are three different
categories of size.
1. The amount of RAM in use, or resident set size, (RSS).
2. The amount of virtual memory address space, (VSS).
3. The amount of swap space allocated or reserved.

Most tools report one of the first two numbers for some set of
regions.

The top command changed in patch PHCO_25204 for 11.11 and PHCO_26020
for 11.00. It used to report the RSS of all regions, but the VSS of
only the classic text, data, and stack region. The newer version
reports VSS for other regions such as shared memory and private mmap
regions.

The amount of RAM held by a process can vary quite a bit depending on
the amount available on the system. The RAM is usually allocated a page
at a time on demand. A process can have some of its memory contents
pushed out to swap. Code and static data from a text area can be paged
in and released without using swap to back it up. Seldom used memory
areas will linger in RAM if there is no other need for that RAM.

There is no single best way to count the size for shared memory
regions. It could be argued that each process is responsible for all or
none of the size of a region that it shares with other processes. The
memory summary in glance actually divides the size of shared memory
regions by the number of processes sharing each region. You can also
use glance to look at the actual list of regions and the RAM used
for each one.

--
Mike Stroyan, mike.stroyan@hp.com