Re: Problems with too much memory (?)

Ingo Molnar (
Sat, 26 Apr 1997 21:20:35 +0200 (MET DST)

On 26 Apr 1997, H. Peter Anvin wrote:

> Followup to: <>
> By author: Tuomas Heino <>
> In newsgroup:
> >
> > MB is propably the cause... but anyway why doesn't Linux support
> > non-cached ram... too complex and/or not worth it? ('swapping' to
> > non-cached ram should still be quite a bit faster than swapping to harddisk)
> >
> Some people have been known to hack the RAMdisk driver to get a RAM
> disk in non-cached memory; then swap to the RAMdisk. This seems to
> work, but I've never seen it supported in the official RAMdisk driver.

btw, this should be fairly easy with a recent kernel, if i'm not missing
something. Use mem=less_by_16M to boot with a certain amount of physical
memory less, then use ioremap_nocache() to grab that memory (people might
want to add a boot option, say nocache_ramdisk=16) ...

i'm not sure how much hacking the ramdisk side needs and wether this
solution is flexible enough (eg. it's a boot-time thing and thus doesnt
support self-resizing ramdisks ... not that we have much chance getting
this done with 4MB pages with whatever technique ...).

if someone goes this way then please tell me and a proper 4mb pages
ioremap can be written too, to keep the ramdisk from trashing the TLB
cache. [btw, does anyone else with big ioremap-ed buffers need a 4MB pages
ioremap? it's not much fun coding it without any RL testing.]

-- mingo