Subject: [RFC PATCH v2 05/11] mm: thp: Correct the HPAGE_PMD_ORDER check.

From: [email-masked] (Steve Capper)
Date: Wed, 8 May 2013 13:03:08 +0100

On Wed, May 08, 2013 at 03:44:17PM +0300, Kirill A. Shutemov wrote:
> On Wed, May 08, 2013 at 10:52:37AM +0100, Steve Capper wrote:
> > All Transparent Huge Pages are allocated by the buddy allocator.
> > 
> > A compile time check is in place that fails when the order of a
> > transparent huge page is too large to be allocated by the buddy
> > allocator. Unfortunately that compile time check passes when:
> > HPAGE_PMD_ORDER == MAX_ORDER
> > ( which is incorrect as the buddy allocator can only allocate
> > memory of order strictly less than MAX_ORDER. )
> 
> It looks confusing to me. Shouldn't we fix what MAX_ORDER means instead?
> 

It confused me as I originally had 13 as the order and couldn't
allocate any 512MB THPs :-).

MAX_ORDER appears to be used quite a lot so I think it would be
safer to change the use case here rather than its meaning.

Cheers,
-- 
Steve