Re: Ram use
- From: Smoot Carl-Mitchell <smoot@xxxxxxx>
- Date: Sat, 20 Jun 2009 20:06:42 -0700
On Sat, 2009-06-20 at 16:13 -0600, Karl Larsen wrote:
I was curious to determine if Kubuntu uses more RAM than Gnome.
Since I have both on my laptop in version 8.10 I decided to try to
measure this. I used top to get the data and I saved the part needed to
gedit which you can get on both kubuntu and gnome. I took data at 10
minutes after boot-up. Here is the data:
You need to be careful about how you interpret these kind of results,
especially on a demand paged virtual memory system like Linux. The more
critical measure for responsiveness (which I think is the critical
measure for a desktop system)is likely the paging rate and especially
the pageout rate. Paging is very expensive when compared to memory
access time. vmstat is a crude, but useful tool to measure this sort of
metric. If you run:
vmstat 5
watch the si and so columns, especially the so column which is the page
out rate to swap. That is a measure of pages being written to the swap
device(s). iostat which is part of the sysstat package can also be
useful.
A more useful test would be to run vmstat 5 or iostat and then operate
the desktop in a typical fashion and see what the paging rate looks like
over time. If you have sufficient memory the page out rate should be
very low. A high paging rate indicates memory starvation and the system
will start to thrash. In vmstat you will see processes blocked waiting
for I/O.
With all this said, I do think running Gnome or KDE with 1GB of memory
is a tad tight with a typical desktop mix of applications. But memory
is very cheap these days and adding memory can be a lot simpler and more
cost effective than trying to optimally tune up the virtual memory
system.
I run a Linux server with 1GB of RAM. It is interesting to watch the
memory utilization over time. The graphs are here:
http://www.c-m.us.com/~smoot/RRD
What you see is the buffer and cache utilization go up significantly
when the system does a lot of I/O. The spikes in the graphs corresponds
to when I run an rsync cron job to do nearline backups. The "free"
memory pool stabilizes at a low percentage over time.
--
Smoot Carl-Mitchell
Computer Systems and
Network Consultant
smoot@xxxxxxx
+1 480 922 7313
cell: +1 602 421 9005
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- From: Karl Larsen
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