too much buffer chache on red hat linux

[Edwin Ruiz_2]

Hi, i need ur help!

I have installed red hat A.S. 3.0 on HP blade servers BL40p and HP Blade SErvers BL20P. that servers have 8 GB RAM but every time i have only 4 MB free, all memory is in Buffer Cache. Oracle has problems to work fine. We want to reduce the buffer cache, how can we do that? on redhat A.S. 7.1 we upgrade the kernel using patches. how can i do that on RH A.S. 3.0 plsa helpme.
I attach free -m output.


total used free shared buffers cached
Mem: 7810 7769 41 0 51 4632
-/+ buffers/cache: 3085 4725
Swap: 16001 214 15786

[rvrameshbabu · Accepted solution]

The buffer chache can be tuned using the below parameter ( /proc/sys/vm/buffermem )

-- default value --
vm.buffermem = 2 10 60
--

The three values in this file correspond to the values in
the struct buffer_mem. It controls how much memory should
be used for buffer memory. The percentage is calculated
as a percentage of total system memory.

The values are:
min_percent -- this is the minimum percentage of memory that should be spent on buffer memory
borrow_percent -- UNUSED in AS 2.1 and RHEL3
max_percent -- UNUSED in AS 2.1 and RHEL3

[Edwin Ruiz_2]

thanks

i was looking for /proc/sys/vm/buffcache but is missing. I just have this files

-rw-r--r-- 1 root root 0 Aug 11 10:57 bdflush
-rw-r--r-- 1 root root 0 Aug 11 10:57 dcache_priority
-rw-r--r-- 1 root root 0 Aug 11 10:57 hugetlb_pool
-rw-r--r-- 1 root root 0 Aug 11 10:57 kswapd
-rw-r--r-- 1 root root 0 Aug 11 10:57 max_map_count
-rw-r--r-- 1 root root 0 Aug 11 10:57 max-readahead
-rw-r--r-- 1 root root 0 Aug 11 10:57 min-readahead
-rw-r--r-- 1 root root 0 Aug 11 10:57 overcommit_memory
-rw-r--r-- 1 root root 0 Aug 11 10:57 overcommit_ratio
-rw-r--r-- 1 root root 0 Aug 11 10:57 pagecache
-rw-r--r-- 1 root root 0 Aug 11 10:57 page-cluster
-rw-r--r-- 1 root root 0 Aug 11 10:57 pagetable_cache


which can i use? how can i change the value?

thanks for ur help

[David Sullivan_7]

Based on your file listing, you must be using Advanced Server 3.0, which doesn't use the same file in /proc. The file /proc/sys/vm/pagecache is the file you want to check out. It has three values: a b c, where "a" is the minimum percentage of RAM to use in the cache, "b" is the percentage to use initially, and "c" is the maximum percentage to use. You can examine current settings by entering "cat /proc/sys/vm/pagecache".

If you want to set these more conservatively, you can do as follows:

echo "1 10 50" > /proc/sys/vm/pagecache

That lets you make immediate changes to the kernel that you can test against your applications.

Once you're happy with a set of values, set them in /etc/sysctl.conf with a line similar to the following:

vm.pagecache = 1 10 50

Hope that helps!