Subj : linux memory
To   : comp.os.linux
From : hopehope_123
Date : Thu Jul 29 2004 12:46 am

Hi 

This is related to linux / oracle , i have asked this question to
oracle support also .

My box is hp , redhat linux advanced server 2.4.18-e.37smp , 4 itanium
64 cpus , 8gb.ram and oracle 9.2.0.5 with rac (2 nodes) . I use ocfs ,
this is a tb.level datawarehouse . My question is related to memory
usage of linux.
Although i have 8gb. of ram , oracle shared memory is about
1.6gb.(ipcs) . My swap size is 24gb. When i check the system by using
top , etc.... , i see most of the memory is used , and a great amount
of memory is used by linux for disk cache. This is the /proc/meminfo
output:
total: used: free: shared: buffers: cached: 
Mem: 8490827776 6121046016 2369781760 0 29163520 1254342656 
Swap: 25165725696 1141850112 24023875584 
MemTotal: 8291824 kB 
MemFree: 2314240 kB 
MemShared: 0 kB 
Buffers: 28480 kB 
Cached: 1040144 kB 
SwapCached: 184800 kB 
Active: 3157680 kB 
Inact_dirty: 401984 kB 
Inact_clean: 16656 kB 
Inact_target: 715264 kB 
HighTotal: 0 kB 
HighFree: 0 kB 
LowTotal: 8291824 kB 
LowFree: 2314240 kB 
SwapTotal: 24575904 kB 
SwapFree: 23460816 kB 
Committed_AS: 16057008 kB 
HugePages_Total: 0 
HugePages_Free: 0 
Hugepagesize: 262144 kB 


Look at the cached value , here it is about 1gb, , this number reaches
up to 6gb. I read some articles about linux memory management ,which
says such a thing is expected behaviour for linux (if there is memory
use it instead of waste) . But the value increase too much that the
machine starts paging. (look at the swap values above) And most
importantly , i use ocfs which uses direct io , so do i get any
benefit of this linux disk cache? (since direct io does not use any os
buffer ) Why does linux incrase the cache size too much and than
starts paging? Whats the benefit of swapping ?  Why does not linux
prevents allocation of cache memory and stop swapping?

 Kind Regards, 
tolga

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