Re: [gentoo-user] Swap performance

[Alex Schuster <wonko@wonkology.org>]

Paul Hartman writes:

> On Wed, May 25, 2011 at 9:20 AM, Alex Schuster <wonko@wonkology.org> wrote:

> I can't remember the last time my swap was used at all. I have 12G of
> RAM, but in my prior system with 8G it was the same. Only in a rare
> case when some program had run-away memory usage/memory leak did I
> ever get to swap usage... I'm using vanilla kernel 2.6.39 with no
> patches, no BFS. And I use proprietary nvidia-drivers. I normally
> don't have so many programs running at once, but it happens sometimes.

Maybe I should have bought 4G instead of 2G, so I'd have 10G, not 8G.
I'm not sure if this is recommended these days, to have one memory bank
with 4G and 3 others with 2G each.

> Since 2.6.38 and enabling automatic process grouping, I don't use nice
> or ionice at all anymore. I do parallel emerge with -j along with make
> -j12 and never notice any slowdown or lag in UI at all.

This is okay now, since I started using the pf-sources. But I have no
explanation, I have been using the BFS scheduler already before with
ck-sources.

> With KDE4 logged in, and no GUI apps running (other than knutmon and
> wicd), my RAM usage is slightly less than 900M (not counting
> filesystem caches).

I don't want to log out now, but I have logs of experiments I did half a
year ago. After a reboot, at the KDM login screen, the +/- buffers/cache
line of free -m output showed 244M used. After logging into KDE4, it's
2954M, but I have maby apps (Konsoles, Kontact, Amarok, TV-Browser,
Dolphin, Chromium) being started automatically.

>> BTW, does anyone else's kwin use 750M? That's pretty high, I think it used
>> to be more like 300M.
> 
> My kwin (4.6.3-r1) has currently 507M VIRT, 54M RES, 37M SHR according to top.

It's growing: 1405m VIRT, 851m RES, 6m SHR. Strange, I did not actually
use the desktop after I wrote the mail you replied to, currently I'm
logged in from remote.
And it grows while I compose this mail, about 1M every 2 minutes. This
is not normal, though.

I use a little script to create a log file with some memory information,
and when I grep these 50 files for the kwin process, I see memory usage
between 410M and 520M mostly. Three were higher, up to 1.4G, but these
were plasma bugs (suddenly haveing eight activities instead of one; and
a problem of the file watcher plasmoid with very large log files).
I also found one log with kwin using only 154M, but that was when I had
KDE 3.5 running :)


> My worst memory offenders, by resident memory:
> clamd 124M
> denyhosts 114M
> X 75M
> plasma-desktop 56M

kwin	851
kontact	385
java	373 (TV-Browser, this is also growing)
X	124
okular	115
chrome	110
chrome	106
mysqld	 93
...

BTW, with each Chromium tab being a single process, I wonder which tab
uses 100M of RAM.


> My PC doesn't swap, but in my Nokia N900, it runs Linux and X, heavy
> use of gtk and Qt4 libs, it has 256M of RAM and 768M of swap on eMMC
> (transfer rate about 20MB/sec). It swaps like crazy. :) Usually there
> is more swap in use than RAM, actually.
> 
> When I move the swap to a slow SD card instead (2MB/sec transfer
> rate), even in that slow device, swapoff on the eMMC swap partition
> with ~500M in-use takes about 2 or 3 minutes at most with the data
> being swapped slowly into the SD card.
> 
> So I think in your case it should be much faster than that!

Or not, with the large access times of hard drive. I don't know how
large the chunks of memory stored in swap are, I thought some megabytes
at least. Does anyone have an idea? I'd ask Volker, but I'm worried
about his gall bladder.


From another mail:

> Or better yet, figure out why his system is swapping at all which is
> what he was going for I think. With 8 GB I think he should be able to
> disable swap entirely anyway. :)

That's what I think, too. As I wrote, I always used to have many
applications open, and in the past this was no problem. If anyone is
interested, there are some screenshots of my desktop here:
http://www.wonkology.org/comp/desktop/
The 2010-11-28 shows the six desktops I have now, shortly after login.
It's made half a year ago, but my desktop still looks quite similar.
right now I have some extra stuff running, but not very much.

And looking at the 3x3 desktops in one image (desktop3x3.png) from 2004,
I see I was using 856M of RAM and 748M of swap then. With a Windows VM,
a Mozilla window, some 15 or more Galeon tabs, and some more stuff.
Without big performance problems. It might have taken a little while
before the Windows VM became fully responsive, but I did not have the
constant swapping I experience now.

	Wonko