Hello list,
On 02/26/2014 12:37 AM, Pierre Malard wrote:
localu@nuage:~# free -h
total used free shared buffers cached
Mem: 4,0G 3,7G 279M 0B 395M 1,8G
-/+ buffers/cache: 1,5G 2,5G
Swap: 1,0G 7,1M 1,0G
but, elsewere, if 5 users needs 1,5 Gb RAM, what about needed RAM for 50?
it doesn't mean that all of that RAM is used for Apache. There are
countless tools to measure RAM usage, but for a quick look, e.g. this
script can be helpful (it just presents some values from proc):
https://raw.github.com/pixelb/ps_mem/master/ps_mem.py
Run it once with apache running and once without, and compare it to
the output of free (column used - cached).
As a summary for the article linked in a previous post
(http://serverfault.com/questions/85470/meaning-of-the-buffers-cache-line-in-the-output-of-free)
and maybe some other readings I've done over time:
Linux thinks: "memory not used = memory wasted". So it will use all the
memory you give at it. If you happen to increase the assigned memory to
your owncloud VM, you'll probably see it fill too, even with the same
software and number of users as now. If i've undestood correctly, if the
kernel has nothing better to do, it uses memory as a filesystem cache
and uses as much as he can (to some limit). If/when later some
application needs the memory it either discards the buffered files to
free some pages or maybe even swaps them off to disk.
Even seeing some swap used is per se not critical. The problem is when
the system is actively/continously swapping or maybe swaping in critical
moments for example when doing a backup or similar. To see if you are
memory bound and thus using swap actively and therefore having
performance problems, you can use the vmstat util (in debian it comes on
the sysstat package).
For example in my laptop right now:
root@portatilmmg:~# free -h
total used free shared buffers cached
Mem: 3,6G 3,2G 408M 0B 196M 1,2G
-/+ buffers/cache: 1,8G 1,7G
Swap: 2,0G 720M 1,3G
you see I have 720Mb of swap, but I really don't care because using
vmstat I can see that swap is not really beeing used:
root@portatilmmg:~# vmstat 5
procs -----------memory---------- ---swap-- -----io---- -system--
----cpu----
r b swpd free buff cache si so bi bo in cs us sy
id wa
0 0 737268 409640 201236 1218112 1 1 59 13 5 4 6 2 91 0
0 0 737268 410332 201264 1214852 0 0 0 310 587 1131 2
2 95 1
0 0 737268 414712 201264 1210612 0 0 0 4 450 884 2 1
97 0
vmstat 5 prints the stats every 5 seconds. Under the header swap, si and
so mean swap in and out, the bytes entering or going out of the swap.
You can see that they are always 0. So swap is not beeing used at all.
There is something stored there for "future" reference, but that's it.
Marcos
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