Upon investigation, it was found that the recommended value for
min_free_kbytes was not reducing the number of fragmentation-related
events that were occuring in the page allocator enough.
This patch increases min_free_kbytes such that at least two pageblocks
are free for MIGRATE_RESERVE and 3 pageblocks free per migratetype that
is commonly used in the page allocator. This significantly reduces the
number of fragmentation-related events that occur.
However, it should be noted that to really get the fragmentation events
down, the upstream kernel needs to have the patch "page-allocator: Limit
the number of MIGRATE_RESERVE pageblocks per zone" applied. It has been
sent for consideration in -mm.
Signed-off-by: Mel Gorman <m...@csn.ul.ie>
---
hugeadm.c | 11 ++++++++++-
1 file changed, 10 insertions(+), 1 deletion(-)
diff --git a/hugeadm.c b/hugeadm.c
index 6ebe153..a793267 100644
--- a/hugeadm.c
+++ b/hugeadm.c
@@ -636,7 +636,16 @@ long recommended_minfreekbytes(void)
}
fclose(f);
- recommended_min = pageblock_kbytes * nr_zones;
+ /* Make sure at least 2 pageblocks are free for MIGRATE_RESERVE */
+ recommended_min = pageblock_kbytes * nr_zones * 2;
+
+ /*
+ * Make sure that on average at least two pageblocks are almost free
+ * of another type, one for a migratetype to fall back to and a
+ * second to avoid subsequent fallbacks of other types There are 3
+ * MIGRATE_TYPES we care about.
+ */
+ recommended_min += pageblock_kbytes * nr_zones * 3 * 3;
return recommended_min;
}
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