Highmem on PPC?

Val Henson val at nmt.edu
Fri Feb 8 08:58:44 EST 2002

On Thu, Feb 07, 2002 at 02:53:19PM -0700, Mark A. Greer wrote:
> Val Henson wrote:
> > Also, I don't think this was a particularly good test of highmem since
> > I don't think many bounce buffers were used, or that the kernel had
> > much reason to map/unmap many highmem pages.  Unfortunately, my SCSI
> > controller isn't working quite right and I can't test with a hard disk
> > as a result.  Any ideas for stressing the system harder?
> You could try lowering max_low_mem.  You can do this by setting "Code
> maturity level option"/"Prompt for advanced kernel configuration options"
> and then going under where you selected HIGH_MEM and setting max_low_mem
> size to something small.
> It will likely take some trial and error to get it stressed enough.
> You'll have to start a bunch or processes and look at where they're
> getting their memory

See, I don't think that user processes using highmem pages is testing
highmem much.  So we have user pages mapped by PTE's - what's changed?
Not a whole lot.  It's when we use bounce buffers in the kernel or ask
the kernel to map user pages or otherwise trigger the kmap/kunmap code
that I'm interested in.


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