Re: [Qemu-devel] [PATCH] add MADV_DONTFORK to guest physical memory

[Andrea Arcangeli <aarcange@redhat.com>]

On Wed, Jan 05, 2011 at 09:00:45PM +0100, Alexander Graf wrote:
> Sure, not all combinations make sense. But "-mem
> size=1G,path=/dev/shm/vm1.ram,populate=on" would make sense, no? TPH

I was referring to Michael's suggestion, sure many options make sense
for mem-path too, in fact populate makes more sense for mem-path
(considering if hugetlbfs allocation fails guest may die if
libhugetlbfs isn't trapping the -ENOMEM and doing munmap creating hole
and replacing hole with regular anoymous memory).

> should go along the same lines here too. It'd just be a flag "tph"
> that defaults to on if available.

THP is already default on (thp only requires us to 2m align the
virtual address of guest physical memory which we should do by default
even for qemu no-kvm). We can add a thp=off switch on the same lines
of ksm=off.

> That way we could also do all the sanity checks in a single place. I
> really like the idea of combining memory management command line
> parameters into a single option :). In the end I'd assume it's
> Anthony's call though.

Ok, let me know ;). Sounds like a lot of trouble compared to
-mem_nomerge, but I agree it may be worth it for the long term.

Thanks,
Andrea