On Fri, Nov 18, 2011 at 05:43:10PM +0100, Marek Szyprowski wrote:
From: Michal Nazarewicz mina86@mina86.com diff --git a/mm/compaction.c b/mm/compaction.c index 6afae0e..09c9702 100644 --- a/mm/compaction.c +++ b/mm/compaction.c @@ -111,7 +111,10 @@ skip:
next: pfn += isolated;
page += isolated;
if (zone_pfn_same_memmap(pfn - isolated, pfn))page += isolated;elsepage = pfn_to_page(pfn);
On Mon, 12 Dec 2011 15:19:53 +0100, Mel Gorman mel@csn.ul.ie wrote:
Is this necessary?
We are isolating pages, the largest of which is a MAX_ORDER_NR_PAGES page. [...]
On Mon, 12 Dec 2011 15:40:30 +0100, Mel Gorman mel@csn.ul.ie wrote:
To be clear, I'm referring to a single page being isolated here. It may or may not be a high-order page but it's still going to be less then MAX_ORDER_NR_PAGES so you should be able check when a new block is entered and pfn_to_page is necessary.
Do you mean something like:
if (same pageblock) just do arithmetic; else use pfn_to_page;
?
I've discussed it with Dave and he suggested that approach as an optimisation since in some configurations zone_pfn_same_memmap() is always true thus compiler will strip the else part, whereas same pageblock test will be false on occasions regardless of kernel configuration.