top or htop? Which one lies?

[Mark Greenwood]

On Sunday 08 Nov 2009 15:21:14 Billie Erin Walsh wrote:
> 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."

Ah, you've clearly never used Windows ;)

Mark

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