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Re: fedora-list Digest, Vol 10, Issue 167



Kshitij Velhal wrote:
> I have a m/c with following config
> Intel Celeron 500MHz
> 450 MB RAM
> ATI 3D Rage Pro 1x/2x AGP
> Microtek 17" Monitor

Well, I have two 433 MHz Celerons and 288 MB RAM, and no performance
complaints...

> The system runs fine except the performance in GUI mode is very very poor.
> 
> By term very very poor I mean:
> 1. Can't switch between applications using Alt+Tab instantly (min 1 sec)
> 2. Minimize/Maximize of window takes time > 3 sec
> 3. If more than 3-4 applications are running it takes >5 sec to show K
> Menu after clicking panel button
> 4. GNumeric Save takes 2-3 sec and more as you use it for sometime
> 5. In Openoffice apps opening Presentations, Docs, Spreadsheets takes
> time 2-3 sec
> 6. If system is running for long time, VLC, Mplayer fail to show video
> only audio is available. Need to restart XServer or sometimes reboot
> to resolve this issue.
> . . .
> 
>  I do see a large Hard disk activity (HDD LED) while doing any of
> these tasks. But CPU usage never goes to 100% and I don't think
> anything hangs... Just the response is very slow.
> 
> The memory usage is always around 400MB. And I don't think there are
> may services running in background.

Ed commented:
> Most people unfortunately read this wrong and telling us you're at 400MB
> unfortunately doesn't mean much since we don't know if you're reading it
> right.  Buffers and cached memory should be treated as "free" memory.

Kshitij Velhal replied:
> Memory usage I mentioned was from output of top command
> ---Sample output---
> Tasks:  76 total,   2 running,  74 sleeping,   0 stopped,   0 zombie
> Cpu(s):  5.2% us,  4.9% sy,  1.0% ni, 88.9% id,  0.0% wa,  0.0% hi,  0.0% si
> Mem:    452204k total,   441960k used,    10244k free,    31304k buffers
> Swap:   473876k total,      912k used,   472964k free,   238196k cached

This is what Ed is talking about.

Memory that is doing absolutely nothing isn't earning its keep. So Linux
tries very hard to use it for something, even if it's only caching a
copy of the files its's read from the hard drive: that will speed things
up if the file is needed again.

In your case, you've got 31304 K + 238196 K = 269500 K or over half your
memory used for buffers and caches. If programs need it, Linux will just
get rid of some of the cache and use that memory.

Windows 2000 does much the same thing, but merely doesn't report buffer
and cache memory as being in use.

Now, that top line does tell us a bit more that's useful. Something's
going on in the background, and that needs 5% of processor time to be
spent in kernel mode. That figure's actually quite high.

I'd like to introduce you to the vmstat command. Type in
vmstat 2
and do one of your six tasks you mentioned. Press Ctrl-C to stop vmstat,
and send us the result. It will give us a basic overview of where your
system is spending its time.

The output of
hdparm /dev/hda
*might* be interesting, too.

> I am worried about physical memory usage.
> I know that SWAP should be double the Physical RAM but I don't have
> space on my HDD. 448MB is I think decent amount of RAM for my work
> habits.

That is a very old, very rough rule of thumb. On some systems it was
necessary to have more swap than main memory, but this isn't the case
for Linux (except on early 2.4 kernels).

If you run out of swap, Bad Things happen. But you knew that. But swap
that is never ever used isn't really earning its keep, either: it's
merely insurance.

You basically aren't using swap, judging by that top screen. Some swap
usage is inevitable: it's when top or vmstat start reporting that you're
actively copying to or from the swap file that you know you're short on
memory.

Hope this helps,

James.
-- 
E-mail address: james | ... and watched Richard Stallman ask one of the
@westexe.demon.co.uk  | waiting staff whether the spring rolls did indeed
                      | spring and whether they would bounce.
                      |     -- Telsa Gwynne


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