Bryan J. Smith <b.j.smith at ieee.org> wrote: > From: Robert Hanson <roberth at abbacomm.net> > >>or should i be more specific with the question(s)? >>the reason i ask is that i just dumped 2 gig dram in a basic >>P4 Intel 3.0GHz box to play with. >>regards and TIA, > > > At more than 1GiB on Linux/x86, you must use a 4G+4G kernel > (this is the default) to see more than 960MiB. This causes a > signficant (10%+) performance hit. On more than 4GiB, it is > worsened as more extensive paging is used. > > If you have 1GiB or less, you should rebuild with_out_ "HIGHMEM" > support which is a 1G+3G kernel, and you'll see better performance > (and memory will be limited to 960MiB). > I thought they have done away with the high memory bounce buffers? Can you explain what Andi means by this? ----quote---- Current X86-64 implementations only support 40 bit of address space, but we support upto 46bits. This expands into MBZ space in the page tables. -Andi Kleen, Jul 2004 ----quote---- Does it mean that we don't need no fancy tweaks to get direct addressing for over 1G or over 4G? Is that hack for Athlons limited/useful only to Athlon MP boards with the Linux option in BIOS or do Opterons also need that?