From: Matt Keenan
Date: Mon Apr 30 2007 - 18:19:02 EST

William Lee Irwin III wrote:
On Sat, 28 Apr 2007 21:26:42 +0100 "Bradley Chapman" <kakadu@xxxxxxxxx> wrote:
Basically, all I want to know is whether or not enabling
CONFIG_HIGHMEM4G for a laptop that has exactly 1GB of RAM will result
in any performance degradation.

On Mon, Apr 30, 2007 at 12:17:55AM -0700, Andrew Morton wrote:
I would expect the advantages of the additional 128MB to considerably
outweigh the cost of turning on CONFIG_HIGHMEM4G.
That cost will be a little extra CPU consumption inside the kernel, but the
great majority of CPU consumption usually happens in userspace anyway.

The CONFIG_VMSPLIT config options were merged for such cases.

It should be able to split on any 4MB-aligned boundary in
CONFIG_HIGHMEM4G. CONFIG_VMSPLIT_3G_OPT appears to do something of
this sort to use an entire 1GB RAM with minimal user address space

This is an ELF ABI violation but the number of major applications
that break is apparently low.

wine and some java implementations being two of the big caveats.


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