top or htop? Which one lies?

[Billie Erin Walsh]

Mark Greenwood wrote:
> On Sunday 08 Nov 2009 08:55:08 Chris Jones wrote:
>   
>> On 7 Nov 2009, at 10:54pm, Mark Greenwood wrote:
>>
>>     
>>> I hope someone on here can clear this up.
>>>
>>> According to top my RAM is as follows:
>>> 2060580k total,  1866728k used,  (which seems to me to be a  
>>> ridiculously enormous amount of RAM to run a bare desktop)
>>> According to htop (which I can't copy and paste)
>>> 269/2012MB (which seems to me to be a quite miraculously small  
>>> amount of RAM to run a bare desktop)
>>>
>>> Which one lies? And why the mahoosive discrepancy?
>>>       
>> Neither. The difference is almost certainly the file cache.
>>
>> ram access is much faster that disk access, and your linux kernel  
>> knows this, so will use any 'unused' ram as a cache of all recently  
>> accessed files, just in case you need them again. This means most  
>> linux system will, after some time of usage, use what might seem like  
>> a surprising large amount of ram, even when you aren't actually  
>> running any applications.
>>
>> The confusion comes because some ways of monitoring memory usage  
>> include the file cache, others don't, since the ram used for the file  
>> cache is only used as long as it is not needed for any other usage. As  
>> soon as it is needed it will be given back. For me, the clearest  
>> utility is the command line 'free' command.
>>
>> So, my bet is your system is using 269MB of ram for real data storage,  
>> and the difference between this and 1867MB is the file cache...
>>
>> Chris
>>
>>
>>     
> Thanks Guys, I knew there were never any simple answers :)
>
> 'free' gives me:
>              total       used       free     shared    buffers     cached
> Mem:       2060580     575336    1485244          0      27332     258848
> -/+ buffers/cache:     289156    1771424
> Swap:      6032368          0    6032368
>
> Which appears to say I have 575336 (KB?) of RAM used, which is closer to what top is telling me today than to what htop is telling me. Another day, 3 different numbers :) Still at least you've cleared up my concern, I know what all that memory is being used for even if I don't know how much :-D
>
> Cheers,
>
> Mark
>   
The easy answer is: "A computer will use all the memory available before it uses the hard drive."

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