Re: RFC: Transparent Hugepage support

[Chris Wright <chrisw@sous-sol.org>]

* Andrea Arcangeli (aarcange@redhat.com) wrote:
> On Tue, Oct 27, 2009 at 04:42:39PM -0400, Christoph Lameter wrote:
> > > 1) hugepages have to be swappable or the guest physical memory remains
> > >    locked in RAM and can't be paged out to swap
> > 
> > Thats not such a big issue IMHO. Paging is not necessary. Swapping is
> > deadly to many performance based loads. You would abort a job anyways that
> 
> Yes, swapping is deadly to performance based loads and it should be
> avoided as much as possible, but it's not nice when in order to get a
> boost in guest performance when the host isn't low on memory, you lose
> the ability to swap when the host is low on memory and all VM are
> locked in memory like in inferior-design virtual machines that won't
> ever support paging. When system starts swapping the manager can
> migrate the VM to other hosts with more memory free to restore the
> full RAM performance as soon as possible. Overcommit can be very
> useful at maxing out RAM utilization, just like it happens for regular
> linux tasks (few people runs with overcommit = 2 for this very
> reason.. besides overcommit = 2 includes swap in its equation so you
> can still max out ram by adding more free swap).

It's also needed if something like glibc were to take advantage of it in
a generic manner.

thanks,
-chris

--
To unsubscribe, send a message with 'unsubscribe linux-mm' in
the body to majordomo@kvack.org.  For more info on Linux MM,
see: http://www.linux-mm.org/ .
Don't email: <a href=mailto:"dont@kvack.org"> email@kvack.org </a>