--Christoph Hellwig [off-list ref] wrote (on Saturday, June 28, 2003 17:08:37 +0100):

On Sat, Jun 28, 2003 at 08:54:36AM -0700, William Lee Irwin III wrote:

quoted

+config HIGHPMD
+	bool "Allocate 2nd-level pagetables from highmem"
+	depends on HIGHMEM64G
+	help
+	  The VM uses one pmd entry for each pagetable page of physical
+	  memory allocated. For systems with extreme amounts of highmem,
+	  this cannot be tolerated. Setting this option will put
+	  userspace 2nd-level pagetables in highmem.

Does this make sense for !HIGHPTE?  In fact does it make sense to
carry along HIGHPTE as an option still? ..

Last time I measured it, it had about a 10% overhead in kernel time.
Seems like a good thing to keep as an option to me. Bill said he
had some other code to alleviate the overhead, but I don't think
it's merged ... I'd rather see UKVA (permanently map the pagetables
on a per-process basis) merged before it becomes "not an option" -
that gets rid of all the kmapping.
 
M.
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