...making Linux just a little more fun!
Mulyadi Santosa [mulyadi.santosa at gmail.com]
Sat, 16 Dec 2006 21:12:28 +0700
After you start a memory-hogger application such as manipulating a large bitmap graphic file, some portions of RAM are likely pushed away to swap. This is normal especially if you have not so big RAM (256MB or less). The problem is, after you finish with this application, whatever you do will be creepingly slow since those pages must be brought back to RAM.
One way you can try is to do these:
# swapoff -a (wait for some seconds... continue after hard disk's LED stops blinking) # swapon -aSwapoff will push everything back to RAM and eventuall disables the swap spaces. Simply execute swapon to enable them again. If you want to play safe, check free output first:
# free -m total used free shared buffers cached Mem: 249 170 79 0 12 45 -/+ buffers/cache: 111 137 Swap: 376 0 376There you can find out that the free RAM (free+buffers+cached) exceeds the size of used swap space (in this case, since nothing is there, it is zero). Knowing this, swapoff will sucessfully push things back to RAM
Another way you can try, is to use swap prefetch feature included in Con Kolivas patchset (-ck). You can find it in kernel.kolivas.org and it's also included in -mm (Andrew Morton) patchset.
I hope this tip is useful for all of LG readers.
Mulyadi Santosa, RHCE
Benjamin A. Okopnik [ben at linuxgazette.net]
Tue, 31 Oct 2006 15:06:37 -0500
Well, I've just learned something important.
In rewriting the mini-MTA I've been working on, "bssmtp", I've stayed with the original code and procedure where I thought they were OK; at least where I assumed they were OK. I just got bitten, hard, by that assumption - with the result that I could send mail to anyone but TAG and Lgang for the past X hours.
Here's the relevant part of my 'bssmtprc':
# Information about the local host domain=linuxmafia.com # domain=linuxgazette.net hostname=Fenrir # Information about the mail relay # preconnect=/usr/bin/ssh -f rick 'sleep 10' preconnect=/usr/bin/ssh -f lg 'sleep 10' mailhost=localhost port=2025 # port=2525In order to switch hosts, I have to flip the 'domain', the 'preconnect', and the 'port' options - and I fat-fingered the first one, so Rick's MTA has been rejecting my mail left and right.
The very next code tweak to go into "bssmtp" is to have a "domain:hostname:port:preconnect" line per *bloody* host. I spent enough hours battling this problem this morning that I never want to do that kind of crap again - or expose anyone else to it.
-- * Ben Okopnik * Editor-in-Chief, Linux Gazette * http://LinuxGazette.NET *