On 04/15/2014 05:18 AM, Vlastimil Babka wrote:
The compaction freepage scanner implementation in isolate_freepages() starts
by taking the current cc->free_pfn value as the first pfn. In a for loop, it
scans from this first pfn to the end of the pageblock, and then subtracts
pageblock_nr_pages from the first pfn to obtain the first pfn for the next
for loop iteration.
This means that when cc->free_pfn starts at offset X rather than being aligned
on pageblock boundary, the scanner will start at offset X in all scanned
pageblock, ignoring potentially many free pages. Currently this can happen when
a) zone's end pfn is not pageblock aligned, or
b) through zone->compact_cached_free_pfn with CONFIG_HOLES_IN_ZONE enabled and
a hole spanning the beginning of a pageblock
This patch fixes the problem by aligning the initial pfn in isolate_freepages()
to pageblock boundary. This also allows to replace the end-of-pageblock
alignment within the for loop with a simple pageblock_nr_pages increment.
Signed-off-by: Vlastimil Babka <vbabka@xxxxxxx>
Reported-by: Heesub Shin <heesub.shin@xxxxxxxxxxx>
Cc: Minchan Kim <minchan@xxxxxxxxxx>
Cc: Mel Gorman <mgorman@xxxxxxx>
Cc: Joonsoo Kim <iamjoonsoo.kim@xxxxxxx>
Cc: Bartlomiej Zolnierkiewicz <b.zolnierkie@xxxxxxxxxxx>
Cc: Michal Nazarewicz <mina86@xxxxxxxxxx>
Cc: Naoya Horiguchi <n-horiguchi@xxxxxxxxxxxxx>
Cc: Christoph Lameter <cl@xxxxxxxxx>
Cc: Rik van Riel <riel@xxxxxxxxxx>
Acked-by: Rik van Riel <riel@xxxxxxxxxx>
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