Disk Cache Usage

-=Graz=- · 04-25-2006, 12:46 AM

i been setting up a laptop today with slackware 10.1. It is a AMD XP 1.4Ghz with 256MB DDR 266 and 40Gb drive.
Have loaded with kernel 2.4.29 and then added bits and pieces to get it workin better on the laptop.. It runs surprisinly well but i notice that the memorry allocated to Disk Cache is 99MB of my 256MB.... This seems a little exessive at a glance.
Just wondering how it should be?
My other laptop uses nearly 200MB disk cache but its got 1024MB ram so its all good....

I also have a 470MB swap space on the AMD unit as well... It does not seem to be gobbling into it at all at this stage...
Just wondering whether 1) this is normal and 2) is it possible to foce the system to use less disk cache and if so, will i suffer a different performance hit?

satinet · 04-25-2006, 02:59 AM

1) This is normal behaviour in linux. The memory will only be used if it's free....

Quote:

If the cache is of a fixed size, it is not very good to have it too big, either, because that might make the free memory too small and cause swapping (which is also slow). To make the most efficient use of real memory, Linux automatically uses all free RAM for buffer cache, but also automatically makes the cache smaller when programs need more memory.

Under Linux, you do not need to do anything to make use of the cache, it happens completely automatically. Except for following the proper procedures for shutdown and removing floppies, you do not need to worry about it.

from http://www.faqs.org/docs/linux_admin/buffer-cache.html

2) This section also implies that it is possible to set a fixed cache size, but i would leave it alone, if I were you....

-=Graz=- · 04-25-2006, 06:04 AM

Hi satinet
That's hit the nail right on the head.. Okay, so it has initially set a large size but will decrease the amount allocated to disk cache to give to applications before it starts using the swap by the looks of things.. which sounds very efficient.
Cool - thanks for this info, great help!