[Linaro-mm-sig] [PATCH 04/15] mm: compaction: introduce isolate_freepages_range()
mel at csn.ul.ie
Mon Jan 30 11:55:48 UTC 2012
On Mon, Jan 30, 2012 at 11:48:20AM +0000, Mel Gorman wrote:
> > + if (!zone)
> > + zone = page_zone(pfn_to_page(pfn));
> > + else if (zone != page_zone(pfn_to_page(pfn)))
> > + break;
> > +
> So what you are checking for here is if you straddle zones.
> You could just initialise zone outside of the for loop. You can
> then check outside the loop if end_pfn is in a different zone to
> start_pfn. If it is, either adjust end_pfn accordingly or bail the
> entire operation avoiding the need for release_freepages() later. This
> will be a little cheaper.
Whoops, silly me! You are watching for overlapping zones which can
happen in some rare configurations and for that checking page_zone()
like this is necessary. You can still initialise zone outside the loop
but the page_zone() check is still necessary.
More information about the Linaro-mm-sig