I've got a kernel module for a video output expansion card that seems to fail when running on a machine with more than 4GB installed. Until the vendor issues a patch for this I want to cap the amount of memory available to the kernel to avoid having to pull the extra memory out of my machine when I do development work on it. I run a lot of VMs the rest of the time so 8GB of main memory comes in handy.

A quick google yielded an article that says appending mem=4G to the boot parameters will do the trick. Is this all I need to do? Is this as good as pulling the memory out?

Should do. The kernel will ignore everything above 4GB and act as if it just wasn't installed.

Not quite. A big chunk (up to 2GB) of the base 4GB of RAM will still end up mapped above the 32-bit boundary, so the card (or driver) will still have issues with pointers that don't fit into 32-bits.

mem=2G is pretty much guaranteed to work, though.

EDIT: /proc/mtrr provides useful feedback on this kind of thing

Cheers

If you give a link to the source code for the driver, I can probably fix it in a few minutes or less..

Cheers

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