linux os cache and ocfs

From: utkanbir <hopehope_123_at_yahoo.com>
Date: 28 Jul 2004 05:41:28 -0700
Message-ID: <f6c90ebe.0407280441.631efb2e@posting.google.com>

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 23gb. 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 linuc 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 ?

Kind Regards,
hope Received on Wed Jul 28 2004 - 07:41:28 CDT