Physicsal/swap Memory Information
Scott_Purcell at Dell.com
Scott_Purcell at Dell.com
Mon Aug 18 14:52:15 CDT 2008
I may be misunderstanding your question, but if you are asking why Linux
shows less memory as "free" than other operating systems it is explained
by a difference in how Linux handles its cache.
As I understand it (and I offer this as a list participant, not as a
Dell representative -- I am not an engineer), Linux bases its memory
management on the statistical likelihood that the code or data that I'm
most likely to need NEXT is very likely to be something that I've needed
RECENTLY. Therefore, it does not routinely clear recently used memory
UNTIL it is needed for something else not already loaded in memory.
This causes memory to nearly always be reported as mostly "used".
The benefit from this is that when you find yourself reusing an
application or data that is still in memory it is MUCH faster since it
only has to be retrieved from memory instead of needing to be loaded
from disk. Here's an example.
* Application A called -- code and data moved from disk to memory (slow)
* Application A executes -- memory shown as used
* Application A is complete -- code and data remain in memory, memory
still shown as used
* Application A is called again -- code and data found in memory (very
fast)
* Application A executes, completes, and exits -- code and data remain
in memory, memory still shown as used
* Application B called -- code and data moved from disk to memory
(slow), first to unallocated memory, then removing (or moving to SWAP)
Application A and its data if needed.
As I understand it, it is generally not regarded as a problem at all
when much of your physical memory is shown as "used" unless you are also
short on free Swap as well.
Does that help answer the question you were intending to ask? Or did I
misinterpret?
Corrections / Clarifications welcome.
Scott
________________________________
From: linux-poweredge-bounces at dell.com
[mailto:linux-poweredge-bounces at dell.com] On Behalf Of ammad shah
Sent: Monday, August 18, 2008 1:50 PM
To: Baird, Josh; linux-poweredge-Lists
Subject: RE: Physicsal/swap Memory Information
Yes Josh
you are right, but why it is in "cached" in windows or Unix clones
"unused memory " is cleared . or garbage recoved
# vmstat
procs -----------memory---------- ---swap-- -----io---- --system--
----cpu----
r b swpd free buff cache si so bi bo in cs us sy
id wa
0 0 160 33476 12772 9963508 0 0 2164 275 1 10 1
1 97 1
________________________________
Subject: RE: Physicsal/swap Memory Information
Date: Mon, 18 Aug 2008 13:45:23 -0500
From: jbaird at follett.com
To: mammadshah at hotmail.com; linux-poweredge at dell.com
The missing memory you are referring to (I think?) is more than likely
being used by kernel processes. More detailed memory statistics can be
obtain by using tools such as vmstat and looking at the contents of
/proc/meminfo.
Thanks,
Josh
From: linux-poweredge-bounces at dell.com
[mailto:linux-poweredge-bounces at dell.com] On Behalf Of ammad shah
Sent: Monday, August 18, 2008 1:39 PM
To: linux-poweredge at dell.com
Subject: Physicsal/swap Memory Information
Hi,
I would like to ask the forum, (again) about Memory utilization. ...from
which tool i will be able to get information of current max utilization
of Memory.
the output of "top" with "M" is
top - 00:16:37 up 6 days, 24 min, 1 user, load average: 0.00, 0.19,
0.45
Tasks: 113 total, 1 running, 112 sleeping, 0 stopped, 0 zombie
Cpu(s): 0.0% us, 0.0% sy, 0.0% ni, 100.0% id, 0.0% wa, 0.0% hi,
0.0% si
Mem: 10231008k total, 10196572k used, 34436k free, 11884k buffers
Swap: 6289408k total, 160k used, 6289248k free, 9963308k cached
PID USER PR NI VIRT RES SHR S %CPU %MEM TIME+ COMMAND
28706 mysql 16 0 408m 93m 3876 S 0.0 0.9 222:51.96 mysqld
2947 root 16 0 21600 9084 1588 S 0.0 0.1 0:01.02 hald
30958 root 16 0 37108 2696 2100 S 0.0 0.0 0:00.01 sshd
2890 root 16 0 21944 2072 1628 S 0.0 0.0 0:00.44 sshd
30960 root 15 0 53988 1628 1216 S 0.0 0.0 0:00.01 bash
28507 root 16 0 53844 1328 1096 S 0.0 0.0 0:00.02 mysqld_safe
2934 dbus 16 0 9672 1240 1072 S 0.0 0.0 0:00.05
dbus-daemon-1
2915 root 16 0 57112 1180 744 S 0.0 0.0 0:00.16 crond
5211 root 16 0 19852 1084 880 S 0.0 0.0 0:00.00 rpc.idmapd
31041 root 16 0 6144 1020 772 R 0.3 0.0 0:00.01 top
9806 root 17 0 8016 976 780 S 0.0 0.0 0:00.00 rpc.mountd
9789 root 18 0 53208 768 648 S 0.0 0.0 0:00.00 rpc.rquotad
9858 rpc 16 0 4744 680 556 S 0.0 0.0 0:00.00 portmap
2737 root 16 0 3624 612 496 S 0.0 0.0 0:00.26 syslogd
1 root 16 0 4748 548 456 S 0.0 0.0 0:00.73 init
2851 root 20 0 2536 536 452 S 0.0 0.0 0:00.00 acpid
2904 root 16 0 4172 532 452 S 0.0 0.0 0:00.00 gpm
2752 root 16 0 2528 492 404 S 0.0 0.0 0:00.01 irqbalance
2741 root 15 0 2532 484 404 S 0.0 0.0 0:00.00 klogd
1232 root 6 -10 3600 452 360 S 0.0 0.0 0:00.01 udevd
2956 root 16 0 2516 404 340 S 0.0 0.0 0:00.00 mingetty
2957 root 18 0 2516 404 340 S 0.0 0.0 0:00.00 mingetty
2958 root 18 0 2516 404 340 S 0.0 0.0 0:00.00 mingetty
2959 root 18 0 2516 404 340 S 0.0 0.0 0:00.00 mingetty
2960 root 22 0 2516 404 340 S 0.0 0.0 0:00.00 mingetty
2961 root 17 0 2516 404 340 S 0.0 0.0 0:00.00 mingetty
2 root RT 0 0 0 0 S 0.0 0.0 0:00.02 migration/0
3 root 34 19 0 0 0 S 0.0 0.0 0:00.00 ksoftirqd/0
4 root RT 0 0 0 0 S 0.0 0.0 0:00.00 migration/1
5 root 34 19 0 0 0 S 0.0 0.0 0:00.00 ksoftirqd/1
6 root RT 0 0 0 0 S 0.0 0.0 0:00.01 migration/2
7 root 34 19 0 0 0 S 0.0 0.0 0:00.00 ksoftirqd/2
as you people can see that top utilization of mysql is "93 M" where as
the output of "free -m" is
# free -m
total used free shared buffers cached
Mem: 9991 9958 33 0 12 9729
-/+ buffers/cache: 215 9775
Swap: 6142 0 6141
where is remaining memory ???????????????.
while i can see the utilization in "GUI" task manger tools .......
any idea. .........
thanks
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