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:

quoted

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