configs: add CONFIG_COMPACTION

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.
We shouldn't disable this option unless there really is a strong reason.

Fixes: #1004

Signed-off-by: Penny Zheng <penny.zheng@arm.com>

kernel/configs/fragments/common/huge.conf

@@ -1,5 +1,10 @@
 # Items to enable large/huge mmu pages and tlbs etc.
 
+# Compaction is the only memory management component to form high order
+# (larger physically contiguous) memory blocks reliably. The lack of the
+# feature can lead to unexpected OOM killer invocations for high order memory requests.
+CONFIG_COMPACTION=y
+
 CONFIG_HUGETLBFS=y
 
 # Enable memory page physical migration here, as it can come

kernel/configs/fragments/common/mmu.conf

@@ -3,4 +3,3 @@
 # vmap the kernel stacks - detects stack over-runs better and reduces
 # the stack attack window.
 CONFIG_VMAP_STACK=y
-