Rik:
My original message for some reason did not seem to make it to the list, so I
am resending this (with some modifications).
I have noticed that kswapd still runs and in when the memory is low, will do
some hard thinking about what to swap even if the system does not have a swap
partition. Here is the proof:
sasha@mysql:/usr/src/linux/mm > free
total used free shared buffers cached
Mem: 254816 248476 6340 0 27224 48832
-/+ buffers/cache: 172420 82396
Swap: 0 0 0
sasha@mysql:/usr/src/linux/mm > ps auxw | grep kswapd
root 5 0.1 0.0 0 0 ? SW Dec19 1:41 [kswapd]
sasha 25619 0.0 0.2 1552 612 pts/7 S 20:34 0:00 grep kswapd
So in this example kswapd essentially wasted 1 min and 41 sec of CPU time.
I have search through the archive and discovered a patch to disable kswapd
through proc at
http://www.uwsg.iu.edu/hypermail/linux/kernel/0108.0/0675.html. I adapted it
to my kernel ( 2.4.17-rc2), disabled kswapd, did some testing and noticed
much better performance.
I would like to request that the above patch in some form be officially
included in the kernel. While a *perfectly working* kswapd on a system with
many different processes behaving in a somewhat unpredicatable manner will be
a boon, there are many instances when running kswapd does more harm than
good. Below are three reasons why a sysadmin may want to have kswapd disabled:
* the system is configured in such a way that it has plenty of RAM for
buffers,cache, and all the processes it will ever run. For example, a
dedicated server machine with lots of RAM, a small server binary, and a set
of files it reads that alltogether will fit into RAM - many MySQL
installations fit into this category. Running kswapd in this case would only
be a waste of CPU
* kswapd has a nasty bug that hogs CPU, causes kernel panic, or swaps out so
aggressively that the system becomes unusable.
* some other code in the kernel does not work well with kswapd - the
particular problem I've run into, for example, was kswapd going crazy trying
to shrink the buffers while find / was causing the kernel to expand them. The
result was kswapd taking up 75% of CPU.
The bottom line is that a sysadmin should have a choice ( isn't that what
Linux is all about, after all?). If he does not want to run kswapd, he should
not have to. If he is really wrong in this, let him find out for himself.
--
MySQL Development Team
For technical support contracts, visit https://order.mysql.com/
__ ___ ___ ____ __
/ |/ /_ __/ __/ __ \/ / Sasha Pachev <sasha@mysql.com>
/ /|_/ / // /\ \/ /_/ / /__ MySQL AB, http://www.mysql.com/
/_/ /_/\_, /___/\___\_\___/ Provo, Utah, USA
<___/
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This archive was generated by hypermail 2b29 : Sun Dec 23 2001 - 21:00:26 EST