[GE users] Difference between "qhost MEMUSE" and "free -m"

reuti reuti at staff.uni-marburg.de
Tue Feb 17 13:20:21 GMT 2009


Hi,

Am 17.02.2009 um 13:58 schrieb futurity:

> I'm using Grid Engine 6.1u3.
>
> I've been told that the qhost MEMUSE value should match the value  
> returned
> by "free -m".  However, I'm noticing a difference between the "free  
> -m" Mem
> used value and the "qhost" MEMUSE value for execution hosts.
>
> 2661 MB compared to 381 MB in one instance.
>
> I know the qhost host value is a snapshot value updated every  
> minute, so I'm
> comparing values at the time this snapshot is taken.  I know these  
> values
> will never be exactly the same, but these differences seems to be very
> large.
>
> I run the command below on a particular execution host to get the  
> values:
>
> # free -m ; qhost | grep stg-dell40
>
>              total       used       free     shared    buffers      
> cached
> Mem:          4048       2661       1387          0         
> 345       1951
> -/+ buffers/cache:        363       3684
> Swap:         2047         50       1997
>
> stg-dell40              lx24-x86        8  2.01    4.0G  381.2M     
> 2.0G
> 50.6M
>
> The "free -m" Mem used (2661 MB) does not match the qhost MEMUSE value
> (381.2 MB).
>
> I've even run it an hour later with top included:
>
> # free -m ; top -b -n1 ; qhost | grep dell40
>              total       used       free     shared    buffers      
> cached
> Mem:          4048        667       3381          0          
> 29        449
> -/+ buffers/cache:        188       3860
> Swap:         2047         51       1996
>
> top - 12:50:03 up 117 days, 21:42,  1 user,  load average: 1.29,  
> 1.83, 3.42
> Tasks: 155 total,   2 running, 153 sleeping,   0 stopped,   0 zombie
> Cpu(s):  5.0%us,  0.3%sy,  0.7%ni, 93.2%id,  0.8%wa,  0.0%hi,  0.0%si,
> 0.0%st
> Mem:   4145700k total,   683584k used,  3462116k free,    30408k  
> buffers
> Swap:  2097136k total,    53056k used,  2044080k free,   460484k  
> cached
>
> stg-dell40              lx24-x86        8  1.87    4.0G  182.5M     
> 2.0G
> 51.8M
>
> Again the "free -m" Mem used (667 MB), confirmed by top, still does  
> not

the 667 include buffers and cache, therefore you have to look at the  
line "-/+ buffers/cache". In Unix like operating systems unused  
memory is bad memory. So, as long as no application uses the memory,  
it's used to speed up the operating system - i.e. to the disk access.  
In this line you see 188.

You can also compute by hand: 677 - 29 (buffers) - 449 (cached) = 189  
(the one is a round-off error)

-- Reuti


> match the qhost MEMUSE value (192.5 MB).
>
> Any idea why these values differ?
>
> Neil
>
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