Messages in this thread | | | Date | Wed, 9 Apr 2008 11:13:07 +0200 | From | Andi Kleen <> | Subject | Re: Does Linux have plan to support memory hole remapping? |
| |
On Wed, Apr 09, 2008 at 05:04:24PM +0800, Zhao Forrest wrote: > On 4/9/08, Andi Kleen <andi@firstfloor.org> 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 > > Yes, I have enabled mem hole remapping in BIOS SETUP. > After looking into dmesg, I found that all 32GB physical memory has > been allocated to 8 nodes, but why MemTotal shows a less amount of > memory than 32GB? Interesting......
There is some loss of memory before MemTotal, both from the BIOS (SMM, Frame Buffer for integrated graphics etc.) and from the kernel (mem_map which costs a few percent and some other data structures which are allocated early)
I covered this in detail in http://halobates.de/memorywaste.pdf
> Does MemTotal means the amount of physical memory allocated to all > nodes? Or it has different meanings?
Amount of memory left over after early boot on all nodes and visible to the kernel (so e.g. minus reservations for kdump kernels)
-Andi
| |