Re: [Qemu-devel] [patch 2/2] i386: pc: align gpa<->hpa on 1GB boundary

[Gleb Natapov]

On Tue, Oct 29, 2013 at 07:21:59PM -0200, Marcelo Tosatti wrote:
> > > Could add a warning to memory API: if memory region is larger than 1GB
> > > and RAM is 1GB backed, and not properly aligned, warn.
> > Perhaps it would be better do abort and ask user to fix configuration,
> > and on hugepage allocation failure not fallback to malloc but abort and
> > tell user amount of hugepages needed to run guest with hugepage backend.
> 
> You want to back your guest with 1GB hugepages. You get 1 such page at a
> time, worst case.
> 
> You either 
> 
> 1) map the guest physical address space region (1GB sized) where
> the hole is located with smaller page sizes, which must be 2MB, see *,
> which requires the user to specify a different hugetlbfs mount path with
> sufficient 2MB huge pages.
> 
Why not really on THP to do the work?

> 2) move the pieces of memory which can't be 1GB mapped backed into
> 1GB hugepages, and map the remaining 1GB-aligned regions to individual 1GB 
> pages.
> 
> I am trying to avoid 1) as it complicates management (and fixes a bug).

--
                        Gleb.