05-07-2012
Quote:
Originally Posted by
learnbash
Actually my main concern is why buffer is 21gb
I will try to put it simple, so the experts might see some detail missing in order to make it easier to understand.
It so, because you told the system (see the values of "maxperm%" and "minperm%" in the output of
vmo -F -a) to preserve a certain amount of memory as free. The rest is first used for programs. When all the programs are loaded and there is still some of this memory available then this will be assigned to caching I/O-operations (this is your "buffer memory"). This assignment is temporary in nature and as soon as there is a program to be started an according amount of memory will be taken away from this buffer memory and given to the program. If some program ends, on the other hand, its memory will not be simply "free" (which means unused), but given to the buffer memory as long as it isn't needed elsewhere.
If you want to reduce buffer memory (which will probably have no adverse effects as far as i can tell) decrease the size of the assigned memory of the LPAR on the HMC profile. This will reduce the size of available memory after fulfilling all the programs requests and therefore less memory will be assigned to I/O-buffers.
Also investigate - together with the DBA! - the possibility of enlarging the SGA. To be honest i wonder how you get away with this much free memory without having the DBA pestering you to get it. In my experience they are a memory-hogging lot.
Btw., as i said before, the system is probably overpowered with respect to the physical CPUs assigned to it too. You might want to investigate possibilities to shrink that back to a sensible amount.
I hope this helps.
bakunin
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LEARN ABOUT DEBIAN
memtester
memtester(8) Maintenance Commands memtester(8)
NAME
memtester - stress test to find memory subsystem faults.
SYNOPSIS
memtester [-p PHYSADDR] <MEMORY> [ITERATIONS]
DESCRIPTION
memtester is an effective userspace tester for stress-testing the memory subsystem. It is very effective at finding intermittent and non-
deterministic faults. Note that problems in other hardware areas (overheating CPU, out-of-specification power supply, etc.) can cause
intermittent memory faults, so it is still up to you to determine where the fault lies through normal hardware diagnostic procedures;
memtester just helps you determine whether a problem exists.
memtester will malloc(3) the amount of memory specified, if possible. If this fails, it will decrease the amount of memory requested until
it succeeds. It will then attempt to mlock(3) this memory; if it cannot do so, testing will be slower and much less effective. Run
memtester as root so that it can mlock the memory it tests.
Note that the maximum amount of memory that memtester can test will be less than the total amount of memory installed in the system; the
operating system, libraries, and other system limits take some of the available memory. memtester is also limited to the amount of memory
available to a single process; for example, on 32-bit machines with more than 4GB of memory, memtester is still limited to less than 4GB.
Note that it is up to you to know how much memory you can safely allocate for testing. If you attempt to allocate more memory than is
available, memtester should figure that out, reduce the amount slightly, and try again. However, this can lead to memtester successfully
allocating and mlocking essentially all free memory on the system -- if other programs are running, this can lead to excessive swapping and
slowing the system down to the point that it is difficult to use. If the system allows allocation of more memory than is actually avail-
able (overcommit), it may lead to a deadlock, where the system halts. If the system has an out-of-memory process killer (like Linux),
memtester or another process may be killed by the OOM killer.
So choose wisely.
OPTIONS
-p PHYSADDR
tells memtester to test a specific region of memory starting at physical address PHYSADDR (given in hex), by mmap(2)ing /dev/mem.
This is mostly of use to hardware developers, for testing memory-mapped I/O devices and similar. Note that the memory region will
be overwritten during testing, so it is not safe to specify memory which is allocated for the system or for other applications;
doing so will cause them to crash. If you absolutely must test a particular region of actual physical memory, arrange to have that
memory allocated by your test software, and hold it in this allocated state, then run memtester on it with this option.
MEMORY the amount of memory to allocate and test, in megabytes by default. You can include a suffix of B, K, M, or G to indicate bytes,
kilobytes, megabytes, or gigabytes respectively.
ITERATIONS
(optional) number of loops to iterate through. Default is infinite.
NOTE
memtester must be run with root privileges to mlock(3) its pages. Testing memory without locking the pages in place is mostly pointless
and slow.
EXIT CODE
memtester's exit code is 0 when everything works properly. Otherwise, it is the logical OR of the following values:
x01 error allocating or locking memory, or invocation error
x02 error during stuck address test
x04 error during one of the other tests
AUTHOR
Written by Charles Cazabon.
REPORTING BUGS
Report bugs to <charlesc-memtester-bugs@pyropus.ca>.
COPYRIGHT
Copyright (C) 2009 Charles Cazabon
This is free software; see the file COPYING for copying conditions. There is NO warranty; not even for MERCHANTABILITY or FITNESS FOR A
PARTICULAR PURPOSE.
memtester 4 July 2009 memtester(8)