Force progams to stay in RAM

SplicedPepper · 09-29-2005, 10:25 AM

Is there a way to force linux to keep certain programs in RAM instead of letting the OS put them into swap file?

Its just two programs that need this done: srcds_l (DoD:Source Dedicated Server) and cod_lnxded (Call of duty Dedicated server, the only reason that this is needed is that theres ftp and http servers on the same box, and overtime ram seems to get eaten by these and not released, which forces the Dedicated servers into swap. This is on a 1gig system btw.

Debian 3.1

Latest Steam / Latest CoD
Apache/2.0.54
ProFTPD 1.2.10 Server

fenderman11111 · 09-30-2005, 02:50 AM

2 things you can possibly do:

1: there is a file salled /proc/sys/vm/swappiness

this file holds a number from 0 - 100, and it dictates how apt Linux is to use swap. (0 meaning not to spap, and 100 meaning to swap alot of stuff). do :

echo 0 > /proc/sys/vm/swappiness

as root, and that should help a lot. to have it set to 0 on every reboot, add this line:

vm/swappiness=0

to the file /etc/sysctl.conf

Also If you ahve enough ram, you can turn off the swap partition altogether (with fluxbox/gaim/galeon/gnome-settings-daemon/multiple gnome-terminals/vmware, i have never exceeded ~300 MB being used, and that's even with Windows running under vmware!)

to turn off a swap partition:

swapoff -a

to turn it back on:

swapon -a

---

hope this helps

-Brandon

foo_bar_foo · 09-30-2005, 04:00 AM

the short answer is NO. You never know what is in physical RAM anyway and you certainly can't and don't want to controll it. It's all managed by the CPUs MMU. The memory stats you get from Linux are just Virtual imaginary memory. Imaginry pages mapped to or pointing to things on disk the CPU thinks it might need. Thats about it plus some data structures like arrays that oint to the pages that point to the things on the disk.
the way the virtual memory works in the 2.6 series kernels is quite good and you shouldn't mess with it.
i think it's important to understand that swap is not just extra RAM
swap is for data that is not backed by media. When non-code non-file non-disk backed data gets generated by a program it immediately goes into the swap que so it can get saved if the system comes under heavy memory preasure. The rest of everything including the executable code itself (the stuff that's really necessary for program execution) just gets tossed out. Ejected i guess is the correct term. So even if your think your system is not using swap the executable code is still not available and needs time (not alot of time) to be reloaded.
It's on the disk anyway so if it's needed later it just gets reread.
Things that haven't been used in a long time are the first to go.
you can run something that goes a little crazy or the server can come under alot of preasure and it looks like the swap stays all used up but all that happens is anonymous data has been saved.
anonymous data that would otherwise be lost and your server would crash. This data can be retrieved if it is needed or it might justt be some memory leak crap that is never needed again. That's all swap is.

All you get wgen you turn off swap is a server that hard crashes.

ironwalker · 09-30-2005, 08:37 AM

Theres an option for this in the kernel...forgot exactly which option handles this so you have to skim through.

JZL240I-U · 09-30-2005, 08:45 AM

Quote:

Originally posted by ironwalker
Theres an option for this in the kernel...

Is that the way live-versions like Knoppix (which have no write access to the disk(s)) work?

enyawix · 09-30-2005, 11:36 AM

this is a easy one buy more ram and just turn swap off. most systems can run on 1gb of ram with no swap.

foo_bar_foo · 09-30-2005, 10:42 PM

i will try again in more simple terms
if you turn off swap you will get this

Code:

99 % cpu  kswapd

and your system will start thrashing the memory like crazy (executable code will get purged and read back in constantly) because RAM it is being forced to hold onto other things it doesn't need at all and therefore can't hold onto the executable code it does need . and it will run like totall crap that is if you are lucky and it doesn't hit the wall and freeze.

There is absolutely no valid reason to disable swap while running a Linux kernel designed to use swap.

enyawix · 10-01-2005, 03:07 AM

Chill man the bulk of what goes into ram on a system with 1gb or more of ram is disk cache. That is why I picked 1gb for what I am saying. I have months of up time gaming no swap on a 2gb system. Running 15k rpm drives I do not need all that disk cache. If you do not have 1gb of ram you need swap. You are almost correct in saying "There is absolutely no valid reason to disable swap while running a Linux kernel designed to use swap." I do not want to give up the disk space. Ram is much cheaper that 15k rpm SCSI disk space.