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