mm: clarify COMPACTION Kconfig text

The current wording of the COMPACTION Kconfig help text doesn't
emphasise that disabling COMPACTION might cripple the page allocator
which relies on the compaction quite heavily for high order requests and
an unexpected OOM can happen with the lack of compaction.  Make sure we
are vocal about that.

Link: http://lkml.kernel.org/r/[email protected]
Signed-off-by: Michal Hocko <[email protected]>
Cc: Markus Trippelsdorf <[email protected]>
Cc: Mel Gorman <[email protected]>
Cc: Joonsoo Kim <[email protected]>
Cc: Vlastimil Babka <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>

diff --git a/mm/Kconfig b/mm/Kconfig
index 78a23c5c302d96ad6ef1198a02deb39a9a6bc228..be0ee11fa0d9ee8ff068244a559a2c52ad96c84c 100644 (file)
--- a/mm/Kconfig
+++ b/mm/Kconfig
@@ -262,7 +262,14 @@ config COMPACTION
        select MIGRATION
        depends on MMU
        help
-         Allows the compaction of memory for the allocation of huge pages.
+          Compaction is the only memory management component to form
+          high order (larger physically contiguous) memory blocks
+          reliably. The page allocator relies on compaction heavily and
+          the lack of the feature can lead to unexpected OOM killer
+          invocations for high order memory requests. You shouldn't
+          disable this option unless there really is a strong reason for
+          it and then we would be really interested to hear about that at
+          [email protected].
 
 #
 # support for page migration