topic cache memory in Operating System - Linux

cache memory

Fadia Almarei — Tue, 22 Mar 2005 10:28:18 GMT

Dear All
i hae Redhat 9 Linux server runs Oracle9i database and Radius service, on the system i upgrade my memory from 1GB to 4GB,but the free memory after the uppgrade is the same as before almost 10GB, i see that the catched memory is big 3.5GB, so for what this cache and how to reduce this value.
BR

Re: cache memory

Vitaly Karasik_1 — Tue, 22 Mar 2005 10:38:03 GMT

the short answer - it's OK; kernel uses all RAM for buffering/caching.

"Understanding Virtual Memory" [http://www.redhat.com/magazine/001nov04/features/vm/] article from RH Magazine may be a good start point for learning Virtual Memory Management in linux kernel.

"Linux Memory Management or 'Why is there no free RAM?" [http://forums.gentoo.org/viewtopic.php?t=175419] provides VM in linux overview and answers the famous question " 'Why is there no free RAM?"

Re: cache memory

Fadia Almarei — Wed, 23 Mar 2005 03:19:31 GMT

Dear Viaty
how can i reduce the valuse of this catch and will this affect the applications run

Re: cache memory

Vitaly Karasik_1 — Wed, 23 Mar 2005 05:00:40 GMT

In general, you should not tuning virtual memory behaviour - the default policy is good for 99% systems.

You shouldn't see any problem with your applications performance because kernel *releases* its buffer/cache when applications need memory.

Re: cache memory

Alexandre Dumont_1 — Fri, 25 Mar 2005 09:31:20 GMT

When looking at memory usage, focus on the line "-/+ buffers/cache:" from the output of the free -tm command:

$ free -tm
total used free shared buffers cached
Mem: 124 113 10 0 2 42
-/+ buffers/cache: 68 55
Swap: 382 124 257
Total: 506 238 267

-> The actual free memory available is 55MB (in this case). 44 MB of theses 55MB are used for the moment by kernel for buffers and cached data, but if you run more proceses they will be released automatically.

Regards
Alex

Re: cache memory

TwoProc — Fri, 25 Mar 2005 12:13:45 GMT

I picked up these tips a while back from a fellow Linux Admin - suggestions he has used to dampen the effects of the Linux demand for buffering.

# inactive_clean_percent default 30. Changed to 60 to free up dirty page faster.
vm.inactive_clean_percent=60

# pagecache default 1 15 30. Use less memory for data cache.
vm.pagecache = 1 5 10