04-26-2012
Shirish,
For test purposes, the easiest way to effectively reduce the amount of physical RAM available for use by processes is to crank up the kernel parameter vm.min_free_kbytes. This sets the low water mark for the amount of memory held as free for new processes and is normally set to something like 50MB. Turning this up to 3.5GB in your example will mean the system will run out of physical memory and start actively paging very quickly. See the man pages for sysctl and sysctl.conf.
This parameter is also very useful for effectively eliminating cache and buffer space when testing I/O throughput.
Of course, the whole point of designing a system configuration is to ensure that the system would only ever actively page as an absolute last resort, one small step better than crashing. Systems should NEVER actively page in normal operation. Disk I/O (milliseconds) is literally a million times slower than RAM operations (nanoseconds), so system performance will immediately become completely unacceptable as soon as the system starts to actively page.
Active paging (shown by "sar -B" or "vmstat") is completely different from swap space usage (shown by "sar -S" or "free"). It's OK for a system to statically park pages of memory for long inactive processes on the swap partition. But, if the system is actively paging, it's reading and writing thousand of blocks to and from swap space per second.
If you even suspect that this system will start actively paging under heavy load, BUY MORE RAM.
Remember to reset vm.min_free_kbytes to the original value when your tests are complete...
Last edited by sds9985; 04-26-2012 at 01:34 AM..
This User Gave Thanks to sds9985 For This Post:
10 More Discussions You Might Find Interesting
1. Programming
Sir,
How can i get the RAM size .Is there is any predefined function ..Howsir???
Thanks In advance,
ArunKumar (6 Replies)
Discussion started by: arunkumar_mca
6 Replies
2. Solaris
;) Hi friends,
any one please help me.
I want to store some job names into an array and also I want extract these names on different timings for scheduling.
Please give me some idea.
your's loving
LOVE :p (1 Reply)
Discussion started by: Love
1 Replies
3. Linux
Hey all,
I have been thinking about getting a new computer, and the motherboard I am looking at is capable of holding up to 8 Gb of ram. Now it appears as though for 32 bit linux, in order to use more than 4 Gb of ram, you had to enable a certain option in the kernel, but if I remember... (2 Replies)
Discussion started by: kermit
2 Replies
4. Red Hat
Hi,
On server 64bit Hw Arch , Linux 5.0(32bit) is installed it is showing only 3gb of ram though physical is 16gb
can u give me idea why? (4 Replies)
Discussion started by: manoj.solaris
4 Replies
5. AIX
Hi ,
I Want to apply AIX lint to my source code which all are *.cpp/*.h
>lint test.cpp
lint: 1286-332 File test.cpp must have a .c, .C or .ln extension. It is ignored.
lint: 1286-334 There are no files to process.
I am getting above error.
-Ashok (3 Replies)
Discussion started by: ashokd001
3 Replies
6. Solaris
I have the processes (100+) by the oracle id and I'd to get the summarized view of the oracle processes' usage of the memory and the cpu.
top would give me some, but not all.
Thanks (3 Replies)
Discussion started by: iwmi
3 Replies
7. Solaris
Hi all, I'm using to Solaris machine. When I run a simple script this messenger come out:"limit: stacksize: Can't remove limit". Any one know the way to resolve this problem without reboot the machine?
Thanks in advance. (3 Replies)
Discussion started by: Diabolist9
3 Replies
8. Red Hat
Hi,
I have a server (BL460c) with 32G of physical RAM.
It currently only uses approx 5% its capacity but will use more (not sure how much more) pending the launch of further applications.
If I need to build another node of similar functionality should I consider downgrading the physical... (2 Replies)
Discussion started by: Duffs22
2 Replies
9. Shell Programming and Scripting
Hi,
How to do Perl script for floating license usages metric. Anyone help me out this issue?
Regards,
Ram. (0 Replies)
Discussion started by: ramanthan
0 Replies
10. Cybersecurity
We have a system with 4 Xeon Processors each with 10 cores, total 512 GB RAM and 10 TB Hard Drive.
we want to create multiple user accounts with different resource limitations as :
User 1: RAM : 50GB, PROCESSOR: 10 Cores , User folder in home directory of 10GB space.
User 2: RAM :... (5 Replies)
Discussion started by: vaibhavvsk
5 Replies
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)