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 PHP
free
FREE(1) User Commands FREE(1)NAME
free - Display amount of free and used memory in the system
SYNOPSIS
free [options]
DESCRIPTION
free displays the total amount of free and used physical and swap memory in the system, as well as the buffers and caches used by the ker-
nel. The information is gathered by parsing /proc/meminfo. The displayed columns are:
total Total installed memory (MemTotal and SwapTotal in /proc/meminfo)
used Used memory (calculated as total - free - buffers - cache)
free Unused memory (MemFree and SwapFree in /proc/meminfo)
shared Memory used (mostly) by tmpfs (Shmem in /proc/meminfo)
buffers
Memory used by kernel buffers (Buffers in /proc/meminfo)
cache Memory used by the page cache and slabs (Cached and SReclaimable in /proc/meminfo)
buff/cache
Sum of buffers and cache
available
Estimation of how much memory is available for starting new applications, without swapping. Unlike the data provided by the cache or
free fields, this field takes into account page cache and also that not all reclaimable memory slabs will be reclaimed due to items
being in use (MemAvailable in /proc/meminfo, available on kernels 3.14, emulated on kernels 2.6.27+, otherwise the same as free)
OPTIONS -b, --bytes
Display the amount of memory in bytes.
-k, --kibi
Display the amount of memory in kibibytes. This is the default.
-m, --mebi
Display the amount of memory in mebibytes.
-g, --gibi
Display the amount of memory in gibibytes.
--tebi Display the amount of memory in tebibytes.
--pebi Display the amount of memory in pebibytes.
--kilo Display the amount of memory in kilobytes. Implies --si.
--mega Display the amount of memory in megabytes. Implies --si.
--giga Display the amount of memory in gigabytes. Implies --si.
--tera Display the amount of memory in terabytes. Implies --si.
--peta Display the amount of memory in petabytes. Implies --si.
-h, --human
Show all output fields automatically scaled to shortest three digit unit and display the units of print out. Following units are
used.
B = bytes
K = kibibyte
M = mebibyte
G = gibibyte
T = tebibyte
P = pebibyte
If unit is missing, and you have exbibyte of RAM or swap, the number is in tebibytes and columns might not be aligned with header.
-w, --wide
Switch to the wide mode. The wide mode produces lines longer than 80 characters. In this mode buffers and cache are reported in two
separate columns.
-c, --count count
Display the result count times. Requires the -s option.
-l, --lohi
Show detailed low and high memory statistics.
-s, --seconds delay
Continuously display the result delay seconds apart. You may actually specify any floating point number for delay using either .
or , for decimal point. usleep(3) is used for microsecond resolution delay times.
--si Use kilo, mega, giga etc (power of 1000) instead of kibi, mebi, gibi (power of 1024).
-t, --total
Display a line showing the column totals.
--help Print help.
-V, --version
Display version information.
FILES
/proc/meminfo
memory information
BUGS
The value for the shared column is not available from kernels before 2.6.32 and is displayed as zero.
Please send bug reports to
<procps@freelists.org>
SEE ALSO ps(1), slabtop(1), top(1), vmstat(8).
procps-ng 2016-06-03 FREE(1)