[CentOS] free memory listing

AshikAli.m ashikali.m at gmail.com
Tue Dec 18 08:57:11 UTC 2012


yes. yes exactly the calculation is correct. In that machine only DRBD and
HA application running.

I tell the story,

I have a telephony server with HA and DRBD mirroring(2 machines) .
Unfortunately I installed 32 bit OS on those. I come to know that after
upgrading it to 64 system will detect all ram memory which are inserted.

In this HA, important process runs on which is production node. For
migration purpose; currently I made machine2 as production node which has
12G ram.

[root at machine2~]# free -m
             total       used       free     shared    buffers     cached
Mem:    12007      11961      46          0        579       9956
-/+ buffers/cache:  1424      10582
Swap:        51199          0      51199

Here,

Used memory ( 12007 - 46  ) = 11961

In that used memory 11961 - ( 579 + 9956 ) = 1429( Actually in use )

so,
46(free)+579(buffer)+9956(cached) = 10581(fraction) is free.


So, Always look into -/+ buffers/cache. That is the exactly correct.

Thanks,
Ashik.








On Tue, Dec 18, 2012 at 10:44 AM, John R Pierce <pierce at hogranch.com> wrote:

> On 12/17/2012 11:19 PM, AshikAli.m wrote:
> > [root at machine1 ~]# free -m
> >               total       used       free     shared    buffers
> cached
> > Mem:    32183       1309      30873          0        290        485
> > -/+ buffers/cache:   533      31649
> > Swap:        51199          0      51199
>
> so you have about 32gb total physical memory.  1.3gb of that is 'used'
> but of that 290MB is buffers and 485MB is cache, so really only 533MB
> (the 2nd line) is in use by software, and 31649MB is available (which is
> the 30873 free on the 1st line, plus the 290 buffers plus the 485
> cached, as all that is considered 'discardable' [*].
>
> you also have 51199MB of swapfile, entirely unused.
>
> this looks to me like a system that was just booted, and hasn't done much.
>
>
> [*] under heavy loads, like a buay large scale database server, this sum
> isn't exactly true, some of the buffer memory is 'dirty' so not
> considered as free without first flushing it to disk...
>
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>



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