On Fri, Nov 02, 2012 at 07:40:11PM +0530, Pritam Bankar wrote: > On Fri, Nov 2, 2012 at 4:26 PM, Mulyadi Santosa > <mulyadi.santosa@xxxxxxxxx> wrote: > > Hi :) > > > > On Fri, Nov 2, 2012 at 5:46 PM, Pritam Bankar > > <pritambankar1988@xxxxxxxxx> wrote: > >> But I have some questions, > >> > >> 1. How is memory split up on 64-bit architecture > > > > in this URL: > > http://unix.stackexchange.com/questions/32244/user-kernel-split-in-64bit-linux > > > > it says user space get 128 TiB...the rest you can read there :) > > > >> 2. Can we override this 3:1 split ? > > > > sure.... just change PAGE_OFFSET if I remember correctly...however, > > the effects might be harmful, for example for certain virtualization > > since they assume certain address for memory allocation > > > >> 3. If yes, who can do that user or kernel? > > > > kernel..for sure.. > > Thanks Mulyadi. I gone through link but there is no explanation. What > can be the logic behind kernel space of only 512 MB for 64-bit > machines. We have 1GB kernel space in 32-bit architecture so 64-bit > should ideally have much more than that. 1, that 512MB is kernel text mapping(kernel image), not kernel space. 2, kernel space under x86_64 is 128TB _now_, same as user space. 3, _now_, the split is 1:1, because address space is large enough. 4, change PAGE_OFFSET is not enough, _now_, under x86_64, PAGE_OFFSET is 0xffff880000000000, the beginning of direct mapping of all phys memory, but the beginning of kernel space is 0xffff800000000000, there is a guard hole between them. Please check https://en.wikipedia.org/wiki/X86-64, and the reasons I underline _now_ are kernel's current design and https://en.wikipedia.org/wiki/X86-64#Canonical_form_addresses PS, if you can read Chinese(hopeless), check my blog: http://adam8157.info/blog/2012/07/linux-x86-64-vm/ -- Regards, Adam Lee http://adam8157.info _______________________________________________ Kernelnewbies mailing list Kernelnewbies@xxxxxxxxxxxxxxxxx http://lists.kernelnewbies.org/mailman/listinfo/kernelnewbies
