On 07/03/2012 09:57 AM, Rik van Riel wrote:

On 07/02/2012 01:42 PM, Sasha Levin wrote:

quoted

On Thu, 2012-06-28 at 14:35 -0700, Andrew Morton wrote:

quoted

On Thu, 28 Jun 2012 17:24:25 -0400 Rik van Riel[off-list ref]  wrote:

quoted

quoted

quoted

@@ -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

I've triggered the following with today's -next:

I've been staring at the migrate code for most of the afternoon,
and am not sure how this is triggered.

At this point, I'm going to focus my attention on addressing
Minchan's comments on my code, and hoping someone who is more
familiar with the migrate code knows how high_pfn ends up
being not pageblock_nr_pages aligned...

migrate_pfn does not necessarily start aligned to a pageblock.

        /* Setup to move all movable pages to the end of the zone */
        cc->migrate_pfn = zone->zone_start_pfn;

In isolate_freepages, high_pfn = low_pfn = cc->migrate_pfn + pageblock_nr_pages /* migrate_pfn doesn't aligned to a pageblock */

-- 
Kind regards,
Minchan Kim

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