Re: [Linaro-mm-sig] [PATCH 03/11] mm: mmzone: introduce zone_pfn_same_memmap()

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;
  

• else
  

• 	page = 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. [...]

This is not true for CMA.

That said, everywhere else managed to avoid checks like this by always scanning in units of pageblocks. Maybe this should be structured the same way to guarantee pfn_valid is called at least per pageblock (even though only once per MAX_ORDER_NR_PAGES is necessary).

I'll look into that.