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List:       suse-linux-e
Subject:    RE: [SLE] OO: If you can make it, I can break it!
From:       "Carlos E. R." <robin1.listas () tiscali ! es>
Date:       2005-12-31 0:38:40
Message-ID: Pine.LNX.4.61.0512310123030.10626 () nimrodel ! valinor
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The Thursday 2005-12-29 at 19:07 -0900, Greg Wallace wrote:

> So when are the binaries cached, when you exit the program?  

No, any file read from disk is cached the first time it is loaded. I don't 
really know if the method is to cache based on disk sectors doing 
read-ahead, or if it is file based, or a mixture: I'm not a kernel 
developer ;-)  Once in cache it stays there unless the memory is needed 
for something else more necessary

> I've really
> never explored this in Linux, but on 'dose, the application binary is cached
> the first time you open it.  That's why if you open something like, say,
> EXCEL, turn right around and close it, then open it again, it comes up
> almost instantly the second time.  You can also go to task manager and watch
> the memory hits.  If an app is, say, 100K, the first time you open it you
> take a 200K memory hit.  If you close it, memory goes down by 100K (leaving
> the 100K cached copy).  The only time that cached copy would go away is if
> you needed the memory for some other app.  Then it would be aged out.  Does
> Linux work differently?

No, that's the idea. Details might be different, of course. I know that 
Linux uses all available memory not used for something else as cache. What 
I remember of windows internals, the memory reserved for cache was fixed: 
time ago there was a direct map (almost) from disk to cache. I'm not sure 
nowdays what it does. 

MsDos had no cache, it was an add on by third parties at first; so they 
must be using a quite complex method now. You may access the disk directly 
bypassing the system: what happens to the cache then? Linux is diferent, 
you access a virtualized filesystem, not the real filesystem below.

- -- 
Cheers,
       Carlos Robinson
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