[uClinux-dev] Most stable 2.4.x kernel for ARM

Jamie Lokier jamie at shareable.org
Fri Feb 20 11:44:34 EST 2009

Michael Schnell wrote:
> >In my particular case kernel uses all available RAM (~10MB) for disk
> >cache and releases it only in ~15 seconds. Other applications cannot
> >be started if one reads large files from disk. I do not experience
> >this problem with 2.4.17 kernel.
> >  
> AFAIK, the Kernel _should_ reduce the disk cache as soon as memory is 
> needed for other purposes (e.g. starting an application). Of course this 
> might take some time for writing back the uncommitted blocks, but of 
> course _much_ less than 15 seconds.

It's all clean data; there is nothing to write back.

It's a common misconception that "free space is wasted space", so it's
ok to fill all the memory with clean page cache.  It comes from the
fact that actually it _is_ good with an MMU, but causes insurmountable
fragmentation problems without an MMU.

> AFAIK, there are several settable (maybe when compiling, maybe at run 
> time) parameters that define the disk cache behavior. Did you take a 
> look at those ?

Certainly, on 2.4, you cannot find suitable settings in a standard 2.4
kernel.  Only the patched uClinux 2.4 kernel works, and I had to patch
it some more.

-- Jamie

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