Messages in this thread | | | Date | Wed, 9 Apr 2008 10:54:40 +0200 | From | Ingo Molnar <> | Subject | Re: Does Linux have plan to support memory hole remapping? |
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* Matti Aarnio <matti.aarnio@zmailer.org> wrote:
> On Wed, Apr 09, 2008 at 10:01:59AM +0200, Andi Kleen wrote: > > "Zhao Forrest" <forrest.zhao@gmail.com> writes: > > > > > > As we can see from above information that the physical memory in system > > > is 32768MB(32GB). However OS is only using about > > > (32768-512)MB(MemTotal: 33010240 kB). Does this mean that this > > > linux kernel can't use the physical memory remapped > > > from (4G-512M, 4G) to (32G, 32G+512M)? > > > > The linux kernel can only use the memory passed to it by the BIOS. > > Sometimes they need special BIOS setup options to enable remapping. If > > there are no such options and you can't upgrade it you're out of luck > > > > I would suggest you contact your system vendor. > > I second that. On my home machine I have early ASUS AMD x64 board > from a few years ago. For it I did buy CPU with this memory mapping > hardware inside, but the BIOS did not support it correctly until a > year or two latter, thus I was not able to use all of 4 GB of memory I > had installed there. There was support in BIOS from start, but it did > things wrong.
having said that - but we'll still consider sane looking patches that allow the remapping of otherwise inactive RAM. [ We might not even have to touch the system chipset beyond what Linux already knows about it: in theory someone might want to try a hack to GART remap such RAM areas and use a sparse mem map entry to map it to Linux - if the identity of that RAM is crystal-clear and there's enough GART space available. But even then it's probably still at best a dangerous and fragile hack. ]
Ingo
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