Re: CMA broken in next-20120926

[Mel Gorman]

> I hope this patch fixes the bug. If this patch fixes the problem
> but has some problem about description or someone has better idea,
> feel free to modify and resend to akpm, Please.
> 

A full revert is overkill. Can the following patch be tested as a
potential replacement please?

---8<---
mm: compaction: Iron out isolate_freepages_block() and isolate_freepages_range() -fix1

CMA is reported to be broken in next-20120926. Minchan Kim pointed out
that this was due to nr_scanned != total_isolated in the case of CMA
because PageBuddy pages are one scan but many isolations in CMA. This
patch should address the problem.

This patch is a fix for
mm-compaction-acquire-the-zone-lock-as-late-as-possible-fix-2.patch

Signed-off-by: Mel Gorman <mgorman@xxxxxxx>
---
 mm/compaction.c |    5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/mm/compaction.c b/mm/compaction.c
index 8250b69..d6e260a 100644
--- a/mm/compaction.c
+++ b/mm/compaction.c
@@ -282,6 +282,7 @@ static unsigned long isolate_freepages_block(struct compact_control *cc,
 {
 	int nr_scanned = 0, total_isolated = 0;
 	struct page *cursor, *valid_page = NULL;
+	unsigned long nr_strict_required = end_pfn - blockpfn;
 	unsigned long flags;
 	bool locked = false;
 
@@ -343,10 +344,10 @@ static unsigned long isolate_freepages_block(struct compact_control *cc,
 
 	/*
 	 * If strict isolation is requested by CMA then check that all the
-	 * pages scanned were isolated. If there were any failures, 0 is
+	 * pages requested were isolated. If there were any failures, 0 is
 	 * returned and CMA will fail.
 	 */
-	if (strict && nr_scanned != total_isolated)
+	if (strict && nr_strict_required != total_isolated)
 		total_isolated = 0;
 
 	if (locked)
--
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