From: William Lee Irwin III <[EMAIL PROTECTED]> >> PAE is useful for more than supporting more than 4GB RAM. It supports >> expanded swapspace and NX executable protections. Some users may want NX >> or expanded swapspace support without the overhead or instability of >> highmem. For these reasons, the following patch divorces CONFIG_X86_PAE >> from CONFIG_HIGHMEM64G.
On Thu, Jul 19, 2007 at 03:52:29PM +0100, Christoph Hellwig wrote: > What overhead of instability of highmem? Sorry folks but this is utter > bollocks. Back in the Caldera days we did a lot of measurement on highmem > overhead, and CONFIG_HIGHMEM has no measurable overhead at all on a system > that doesn't use it. CONFIG_HIGHMEM64G on the other hand has > a quite visible overhead on small systems, but that's entirely due to the > bigger page table entries that you need for NX. The missing context here is CONFIG_VMSPLIT on laptops. Laptop users, who frequently use CONFIG_VMSPLIT options to avoid highmem, wanted to turn on NX. Prior to the patch, those options were barred for all highmem configurations. In response to those requests, I produced the patch. The overhead and instability derived from tiny zones as opposed to kmap()/kunmap(), or at least such was the case historically. -- wli - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
