On Thu, 28 Jun 2012 17:24:25 -0400
Rik van Riel <riel@xxxxxxxxxx> wrote:
>
> >> @@ -463,6 +474,8 @@ static void isolate_freepages(struct zone *zone,
> >> */
> >> if (isolated)
> >> high_pfn = max(high_pfn, pfn);
> >> + if (cc->order> 0)
> >> + zone->compact_cached_free_pfn = high_pfn;
> >
> > Is high_pfn guaranteed to be aligned to pageblock_nr_pages here? I
> > assume so, if lots of code in other places is correct but it's
> > unobvious from reading this function.
>
> Reading the code a few more times, I believe that it is
> indeed aligned to pageblock size.
I'll slip this into -next for a while.
--- a/mm/compaction.c~isolate_freepages-check-that-high_pfn-is-aligned-as-expected
+++ a/mm/compaction.c
@@ -456,6 +456,7 @@ static void isolate_freepages(struct zon
}
spin_unlock_irqrestore(&zone->lock, flags);
+ WARN_ON_ONCE(high_pfn & (pageblock_nr_pages - 1));
/*
* Record the highest PFN we isolated pages from. When next
* looking for free pages, the search will restart here as
_
> >> --- a/mm/internal.h
> >> +++ b/mm/internal.h
> >> @@ -118,8 +118,10 @@ struct compact_control {
> >> unsigned long nr_freepages; /* Number of isolated free pages */
> >> unsigned long nr_migratepages; /* Number of pages to migrate */
> >> unsigned long free_pfn; /* isolate_freepages search base */
> >> + unsigned long start_free_pfn; /* where we started the search */
> >> unsigned long migrate_pfn; /* isolate_migratepages search base */
> >> bool sync; /* Synchronous migration */
> >> + bool wrapped; /* Last round for order>0 compaction */
> >
> > This comment is incomprehensible :(
>
> Agreed. I'm not sure how to properly describe that variable
> in 30 or so characters :)
>
> It denotes whether the current invocation of compaction,
> called with order > 0, has had free_pfn and migrate_pfn
> meet, resulting in free_pfn being reset to the top of
> the zone.
>
> Now, how to describe that briefly?
Use a multi-line comment above the definition ;)
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