[PATCH mm-unstable 1/4] mm/khugepaged: Use minimal bits to store num page < HPAGE_PMD_NR

["Zach O'Keefe" <zokeefe@google.com>]

Minimally, node_load[] entries just need to be able to hold the maximum
value of HPAGE_PMD_NR, which is compile-time defined per-arch based on
PMD_SHIFT and PAGE_SHIFT.  node_load[] is only written either via memset(),
or with via post-increment. struct collapse_control may be allocated
via kmalloc() in other collapse contexts, and MAX_NUMNODES may be
arbitrarily large. #define the underlying type of node_load[] based off
HPAGE_PMD_NR to avoid excessive memory allocated for this struct.

Fixes: 3b07f3bb225a ("mm/khugepaged: add struct collapse_control")
Link: https://lore.kernel.org/linux-mm/Ys2CeIm%2FQmQwWh9a@google.com/
Signed-off-by: Zach O'Keefe <zokeefe@google.com>
---
 mm/khugepaged.c | 7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

diff --git a/mm/khugepaged.c b/mm/khugepaged.c
index 69990dacde14..ecd28bfeab60 100644
--- a/mm/khugepaged.c
+++ b/mm/khugepaged.c
@@ -92,8 +92,11 @@ struct collapse_control {
 	bool is_khugepaged;
 
 	/* Num pages scanned per node */
-	int node_load[MAX_NUMNODES];
-
+#if HPAGE_PMD_ORDER < 16
+	u16 node_load[MAX_NUMNODES];
+#else
+	u32 node_load[MAX_NUMNODES];
+#endif
 	/* Last target selected in hpage_collapse_find_target_node() */
 	int last_target_node;
 };
-- 
2.37.0.170.g444d1eabd0-goog