RE: discontig patch question

["Seth, Rohit" <rohit.seth@intel.com>]

In my opinion since the other zone build functions depend on (1UL <<
MAX_ORDER -1) for forcing the zone alignment, so the same should be used
here in ORDERSDOWN also.  If that seems too aggressive for any reason
then you should change the ORDERROUNDDOWN minimally to have (PAGE_SIZE
<< (MAX_ORDER -1)).  That should align the modules at 4G boundary for
16K PAGE_SIZE. 

Hugetlb needs certain order (of NORMAL_PAGE_SIZE)of contiguous pages to
be available for allocation.  The start of this allocation needs to be
at least HUGE_PAGE_SIZE_ALIGNED.  And I think that part is guaranteed by
buddy page_allocator(while allocating a certain order of pages).


rohit

> -----Original Message-----
> From: Jesse Barnes [mailto:jbarnes@sgi.com]
> Sent: Monday, November 10, 2003 11:09 AM
> To: Van Maren, Kevin
> Cc: Seth, Rohit; linux-ia64@vger.kernel.org
> Subject: Re: discontig patch question
> 
> On Mon, Nov 10, 2003 at 12:34:47PM -0600, Van Maren, Kevin wrote:
> > > Yeah, but 1UL<<MAX_ORDER will always be page aligned, right?
> >
> > Only if MAX_ORDER >= PAGE_SHIFT.
> >
> > But page alignment isn't the question: it is already aligned to
> > the 16MB or 64MB granules.
> 
> Right.  Spaced out there for a minute...
> 
> > But you are saying that the address doesn't have to be as strict:
> > even if allocating 2^MAX_ORDER _pages_, the start doesn't have to
> > be aligned at a natural (PAGE_SIZE<<MAX_ORDER) boundary, and that
> > we can change the ORDERROUNDDOWN to not be as aggressive.
> 
> Well, strictly speaking I don't think start _has_ to align on those
> conditions, but the hugetlb stuff may that it does (I haven't looked).
> 
> > But then it also makes sense to have a smaller MAX_ORDER when not
> > using 4GB hugepages?  I'm happy with <= 256MB hugepages with 16GB
ram,
> > so I guess I'd rather MAX_ORDER was normally smaller, and increased
> > only with very large hugepage pages.
> 
> That makes sense to me.  It seems like FORCE_MAX_ZONEORDER should
depend
> on HUGETLB_PAGE_SIZE_* so that we don't apply unnecessary alignment
> constraints.  Of course, there's probably something I'm missing, Rohit
> might know more.
> 
> Jesse