The ifdefs are not technically needed here, everything used here is
always defined, so switch to IS_ENABLED() to make things a little less
tiresome to read.

Also, Vlastimil pointed out that the VM_BUG_ON()s have fallen out of
favour, so remove them.

Reviewed-by: Vlastimil Babka (SUSE) <vbabka@kernel.org>
Signed-off-by: Brendan Jackman <jackmanb@google.com>
---

>> And it's all internal to page alloc so I'd just drop those checks
>> completely at this point.
>
> But, I won't die on the above hill, if people really hate BUG that much
> happy to go with the flow.
>
> In that case, I'd suggest we drop them as a separate patch.

Oh, actually no, the VM_BUG_ONs were the main thing making the ifdefs
awkward, it makes sense to drop them together. Here's a combined patch.

 mm/page_alloc.c | 25 ++++++++-----------------
 1 file changed, 8 insertions(+), 17 deletions(-)

diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 5d6144c8860ed..76d5d9464e2ef 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -650,19 +650,12 @@ static void bad_page(struct page *page, const char *reason)
 
 static inline unsigned int order_to_pindex(int migratetype, int order)
 {
+	if (IS_ENABLED(CONFIG_TRANSPARENT_HUGEPAGE)) {
+		bool movable = migratetype == MIGRATE_MOVABLE;
 
-#ifdef CONFIG_TRANSPARENT_HUGEPAGE
-	bool movable;
-	if (order > PAGE_ALLOC_COSTLY_ORDER) {
-		VM_BUG_ON(!is_pmd_order(order));
-
-		movable = migratetype == MIGRATE_MOVABLE;
-
-		return NR_LOWORDER_PCP_LISTS + movable;
+		if (order > PAGE_ALLOC_COSTLY_ORDER)
+			return NR_LOWORDER_PCP_LISTS + movable;
 	}
-#else
-	VM_BUG_ON(order > PAGE_ALLOC_COSTLY_ORDER);
-#endif
 
 	return (MIGRATE_PCPTYPES * order) + migratetype;
 }
@@ -671,12 +664,10 @@ static inline int pindex_to_order(unsigned int pindex)
 {
 	int order = pindex / MIGRATE_PCPTYPES;
 
-#ifdef CONFIG_TRANSPARENT_HUGEPAGE
-	if (pindex >= NR_LOWORDER_PCP_LISTS)
-		order = HPAGE_PMD_ORDER;
-#else
-	VM_BUG_ON(order > PAGE_ALLOC_COSTLY_ORDER);
-#endif
+	if (IS_ENABLED(CONFIG_TRANSPARENT_HUGEPAGE)) {
+		if (pindex >= NR_LOWORDER_PCP_LISTS)
+			order = HPAGE_PMD_ORDER;
+	}
 
 	return order;
 }
-- 
2.51.2