tree:   git://git.cmpxchg.org/linux-mmotm.git master
head:   9567896580328249f6519fda78cf9fe185a8486d
commit: c39888c6bc250dd501d64938ed3b8f040eb75988 [219/459] mm/compaction: avoid rescanning pageblocks in isolate_freepages
config: x86_64-rhel (attached as .config)

Note: it may well be a FALSE warning. FWIW you are at least aware of it now.
http://gcc.gnu.org/wiki/Better_Uninitialized_Warnings

All warnings:

   mm/compaction.c: In function 'compaction_alloc':
>> mm/compaction.c:773:15: warning: 'next_free_pfn' may be used uninitialized in this function [-Wmaybe-uninitialized]
     cc->free_pfn = next_free_pfn;
                  ^
   mm/compaction.c:688:16: note: 'next_free_pfn' was declared here
     unsigned long next_free_pfn; /* start pfn for scaning at next round */
                   ^

vim +/next_free_pfn +773 mm/compaction.c

c39888c6 Vlastimil Babka   2014-05-10  757  		 * highest pageblock we isolated pages from.
ff9543fd Michal Nazarewicz 2011-12-29  758  		 */
c39888c6 Vlastimil Babka   2014-05-10  759  		if (isolated)
c89511ab Mel Gorman        2012-10-08  760  			cc->finished_update_free = true;
ff9543fd Michal Nazarewicz 2011-12-29  761  	}
ff9543fd Michal Nazarewicz 2011-12-29  762  
ff9543fd Michal Nazarewicz 2011-12-29  763  	/* split_free_page does not map the pages */
ff9543fd Michal Nazarewicz 2011-12-29  764  	map_pages(freelist);
ff9543fd Michal Nazarewicz 2011-12-29  765  
7ed695e0 Vlastimil Babka   2014-01-21  766  	/*
7ed695e0 Vlastimil Babka   2014-01-21  767  	 * If we crossed the migrate scanner, we want to keep it that way
7ed695e0 Vlastimil Babka   2014-01-21  768  	 * so that compact_finished() may detect this
7ed695e0 Vlastimil Babka   2014-01-21  769  	 */
7a071c0b Joonsoo Kim       2014-05-10  770  	if (block_start_pfn < low_pfn)
3f52bb23 Vlastimil Babka   2014-05-10  771  		next_free_pfn = cc->migrate_pfn;
70dbb548 Vlastimil Babka   2014-05-10  772  
70dbb548 Vlastimil Babka   2014-05-10 @773  	cc->free_pfn = next_free_pfn;
ff9543fd Michal Nazarewicz 2011-12-29  774  	cc->nr_freepages = nr_freepages;
748446bb Mel Gorman        2010-05-24  775  }
748446bb Mel Gorman        2010-05-24  776  
748446bb Mel Gorman        2010-05-24  777  /*
748446bb Mel Gorman        2010-05-24  778   * This is a migrate-callback that "allocates" freepages by taking pages
748446bb Mel Gorman        2010-05-24  779   * from the isolated freelists in the block we are migrating to.
748446bb Mel Gorman        2010-05-24  780   */
748446bb Mel Gorman        2010-05-24  781  static struct page *compaction_alloc(struct page *migratepage,

:::::: The code at line 773 was first introduced by commit
:::::: 70dbb54803fa59e35e72d1710946e8596af31480 mm/compaction: cleanup isolate_freepages()

:::::: TO: Vlastimil Babka <vbabka@suse.cz>
:::::: CC: Johannes Weiner <hannes@cmpxchg.org>

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