An active RHEL system should be using almost all of the free physical memory for cache and buffers. Once you start doing application I/O, you'll see the memory get "used" by the OS quickly. Remember, the memory "used" for cache/buffers is actually free and the kernel can reclaim it very quickly if memory demand for processes increases. The "free" command shows you the difference between "used" memory with and without including the cache/buffers.
Older versions of Linux did have a penalty for very large memory because the algorithms used to manage memory pages were primitive. Many of those problems were addressed in later RHEL 4 releases and by the time we got to RHEL 5 and 6, those issues have been completely resolved. Many of our servers run 256 or 512GB of RAM. For a BL460c with maybe 8 cores, 32GB seems to me to be about right. If it's a BL460cG6 with 16 cores, 32GB seems small. It all depends on what applications or databases you're running on it.
Here's an example from a mid range system with 48 cores:
At first glance it looks like this system has no free memory. But the actual memory used by processes is actually only 24GB - the other 226GB is cache/buffers.
With very large amounts of RAM on certain hardware you can encounter NUMA issues, but as a general rule, you can never have too much memory. RHEL will find a way to use it.
Hello,
I need explanations about physical disks and physical volumes. What is the difference between these 2 things?
In fact, i am trying to understand what the AIX lspv2command does.
Thank you in advance. (2 Replies)
I was in smit, checking on disc space, etc. and it appears that one of our physical volumes that is part of a large volume group, has no free physical partitions. The server is running AIX 5.1. What would be the advisable step to take in this instance? (9 Replies)
Hi All,
I am trying to find the physical memory usage by each process/users.
Can you please let me know how to get the memory usage?.
Thanks,
bsraj. (12 Replies)
Hello All,
Can anybody please tell me what is the maximum limit of Physical IBM Power Machine which can be handled by single HMC at a single point of time?
Thanks,
Jenish (1 Reply)
I have a Sun T5120, and I want to programmatically determine how much RAM it has.
# uname -a
SunOS myhost 5.10 Generic_141444-09 sun4v sparc SUNW,SPARC-Enterprise-T5120
The box has 64Gb; I tried prtdiag and prtconf, but they give me bogus info
prtconf gives me:
# prtconf |grep -i... (12 Replies)
After a memory upgrade all network interfaces are misconfigued. How do i resolve this issue. Below are some out puts.thanks.
ifconfig: plumb: SIOCLIFADDIF: eg000g0:2: no such interface
# ifconfig eg1000g0:2 plumb
ifconfig: plumb: SIOCLIFADDIF: eg1000g0:2: no such interface
# ifconfig... (2 Replies)
Hi,
I am new to unix. I am working on Red Hat Linux and side by side on AIX also. After reading the concepts of Storage, I am now really confused regarding the terminologies
1)Physical Volume
2)Volume Group
3)Logical Volume
4)Physical Partition
Please help me to understand these concepts. (6 Replies)
Hi,
kstat -p -m zfs -n arcstats -s size returns
zfs:0:arcstats:size 8177310584
this values is approx (7.61 GB)
but my Physical Memory size is only 6144 Megabytes.
Can this happen ?
if yes, then how can I find free memory on the system.
BTW, I ran the kstat commands from a Non... (2 Replies)
Discussion started by: sapre_amit
2 Replies
LEARN ABOUT DEBIAN
dphys-swapfile
DPHYS-SWAPFILE(8) System Manager's Manual DPHYS-SWAPFILE(8)NAME
dphys-swapfile - set up, mount/unmount, and delete an swap file
SYNOPSIS
dphys-swapfile setup|swapon|swapoff|uninstall
DESCRIPTION
dphys-swapfile computes the size for an optimal swap file (and resizes an existing swap file if necessary), mounts an swap file, unmounts
it, and and delete it if not wanted any more.
OPTIONS
There is only one parameter, an command, which can be either of these:
setup Tells dphys-swapfile to compute the optimal swap file size and (re-)generate an fitting swap file. Default it 2 times RAM size. This
can be called at boot time, so the file allways stays the right size for current RAM, or run by hand whenever RAM size has changed.
swapon and swapoff These run the swapon and swapoff commands on the swapfile. Note that direct swapon/off from /etc/fstab is not possible,
as that is (at least on Debian) done in the same script that mounts /var (which is where the swap file most likely resides). And we
need to do our setup between those actions. So pass up /etc/fstab, and do our own swapon/off.
uninstall
Gets rid of an unwanted swap file, reclaiming the disk space.
CONFIG
The config file /etc/dphys-swapfile allows the user to set up the working environment for dphys-swapfile.
This config file is a sh script fragment full of assignments, which is sourced. Standard sh syntax rules apply. Assignments are:
CONF_SWAPFILE
Set where the swap file should be placed. Defaults to /var/swap. It is unlikely that you will need to change this, unless you have
very strange partitioning, and then you will most likely be using an swap partition anyway.
CONF_SWAPSIZE
Force file size to this. Default is 2*RAM size. This is unlikely to be needed, unless in strange diskspace situations. Note that
swap enabled and smaller than RAM causes kernal-internal VM trouble on random systems.
CONF_SWAPFACTOR
Set the relation between RAM and swap size. Must be an integer. Defaults to 2 which means swap size = 2 * RAM size
CONF_MAXSWAP
Set maximum size of the swap file in MBytes. Defaults to 2048 which was the former kernel limit for the swapfile size and is now a
limit to prevent unusual big swap files on systems with a lot of RAM.
FILES
/etc/dphys-swapfile
user config
$CONF_SWAPFILE
the swap file, target of the whole action (defaults to /var/swap)
EXAMPLES
dphys-swapfile is usually run at system startup and shutdown from an /etc/init.d (or /etc/rc.d) script, such as this (minimal) one:
#!/bin/sh
# /etc/init.d/dphys-swapfile - automatically set up an swapfile
# author franklin, last modification 2004.06.04
# This script is copyright ETH Zuerich Physics Departement,
# use under either modified/non-advertising BSD or GPL license
case "$1" in
start)
/sbin/dphys-swapfile setup
/sbin/dphys-swapfile swapon
;;
stop)
/sbin/dphys-swapfile swapoff
;;
esac
exit 0
If an sysadmin wants to have his swapfile in annother place, say /var/run/swap, he can use:
In /etc/dphys-swapfile:
CONF_SWAPFILE=/var/run/swap
AUTHOR
franklin@phys.ethz.ch, http://www.phys.ethz.ch/~franklin/
D-PHYS Swapfile Tools 2006.09.15 DPHYS-SWAPFILE(8)