Messages in this thread | | | Date | Wed, 9 Apr 2008 11:02:22 -0700 | From | "Yinghai Lu" <> | Subject | Re: Does Linux have plan to support memory hole remapping? |
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On Wed, Apr 9, 2008 at 3:03 AM, Andi Kleen <andi@firstfloor.org> wrote: > > On Wed, Apr 09, 2008 at 11:50:00AM +0200, Arne Georg Gleditsch wrote: > > Andi Kleen <andi@firstfloor.org> writes: > > > > > "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 > > > > Hm, wouldn't the given e820 map and mtrr listing indicate that 512M were > > actually remapped to 32G+ in this case? > > The way it usually works (if it is implemented correctly in the BIOS) > is that all memory starting at the hole moves up together > (often subject to DIMM boundaries etc.), > not that the area below the hole is remapped individually. > > BTW it is not actually 512MB that is lost. MemTotal does not > include mem_map and that alone is ~512MB (64 bytes for each 4K page) > > So as far as I can see there is no missing memory remapping in Zhao's case, > he's just confused by the MemTotal semantics.
agreed. the HW/BIOS already enable HW memory hole.
YH
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