Re: Do not depend on MAX_ORDER when grouping pages by mobility

On Mon, 12 Nov 2007 15:54:53 +0000 mel@skynet.ie (Mel Gorman) wrote:

Ordinarily, the size of a pageblock is determined from the hugepage size.
On PPC64, the hugepage size is determined at runtime based on the ability
of the machine. If the machine does not support hugepages, HPAGE_SHIFT is
0. This results in pageblock_order being set to -PAGE_SHIFT and a crash
results shortly afterwards.

This patch checks that HPAGE_SHIFT is a sensible value before using the
hugepage size. If it is 0, MAX_ORDER-1 is used instead as this is a sensible
value of pageblock_order.

Signed-off-by: Mel Gorman <redacted>

Looks good. Legacy iSeries boots fine with this and David Gibson has run
his libhugetlbfs test suite on a Power5+ machine also running the same
kernel (ppc64_defconfig).

I would be good if we could get this in for 2.6.24 (since, as far as
legacy iSeries is concerned, this is a regression from 2.6.23).  I am not
sure what other testing needs to be done.

-- 
Cheers,
Stephen Rothwell                    sfr@canb.auug.org.au
http://www.canb.auug.org.au/~sfr/