Subject: disable migrate_prep()

From: Andrea Arcangeli <aarcange@redhat.com>

I get trouble from lockdep if I leave it enabled:

=======================================================
[ INFO: possible circular locking dependency detected ]
2.6.34-rc3 #50
-------------------------------------------------------
largepages/4965 is trying to acquire lock:
 (events){+.+.+.}, at: [<ffffffff8105b788>] flush_work+0x38/0x130

 but task is already holding lock:
  (&mm->mmap_sem){++++++}, at: [<ffffffff8141b022>] do_page_fault+0xd2/0x430


flush_work apparently wants to run free from lock and it bugs in:

	lock_map_acquire(&cwq->wq->lockdep_map);

Signed-off-by: Andrea Arcangeli <aarcange@redhat.com>
---

diff --git a/mm/compaction.c b/mm/compaction.c
--- a/mm/compaction.c
+++ b/mm/compaction.c
@@ -383,7 +383,9 @@ static int compact_zone(struct zone *zon
 	cc->free_pfn = cc->migrate_pfn + zone->spanned_pages;
 	cc->free_pfn &= ~(pageblock_nr_pages-1);
 
+#if 0
 	migrate_prep();
+#endif
 
 	while ((ret = compact_finished(zone, cc)) == COMPACT_CONTINUE) {
 		unsigned long nr_migrate, nr_remaining;