On Sat, 28 Nov 2009 12:07:16 +1000 Shane <ibm-m...@tpg.com.au> wrote:
> I missed the earlier part of this thread, but is large page support even > in z/VM ?. Alan ?. > I have a recollection that Mario Held from the Boeblingen labs said this > has been tested, but only for an LPAR install. And I'm pretty sure I > followed up on this and got the answer it's not even in V6.1. > Happy to be proved wrong. Large page support is not available in z/VM, in particular guest support is pretty hard to do. But the nice thing is: you don't need guest support to reap the main benefit of large pages. There are two benefits: 1) Less TLB entries for the same amount of addressed shared memory. 2) Reduced memory overhead for the page tables to map the shared memory. You get TLB saving only on LPAR with the hardware support but you can get the page table savings on z/VM with a little trick. Allocate huge pages like you do if you have the hardware support. Then in addition allocate a page table page to map the huge page and associate it with the huge page. When the huge page is mapped to a process use the same page table for all mappers. Sort of a poor man page table sharing. This trick works on z/VM and on older machines that do not even have large pages. > On non-s390 one of the big plusses is avoiding TLB misses. But given > that I believe z/VM also doesn't support hiperdispatch, that may not be > much of a gain on zSeries either. I don't see the connection between TLB misses and hiperdispatch. Could you elaborate please? -- blue skies, Martin. "Reality continues to ruin my life." - Calvin. ---------------------------------------------------------------------- For LINUX-390 subscribe / signoff / archive access instructions, send email to lists...@vm.marist.edu with the message: INFO LINUX-390 or visit http://www.marist.edu/htbin/wlvindex?LINUX-390
