mm: page_alloc: use the correct THP order for THP PCP

Commit 44042b44 ("mm/page_alloc: allow high-order pages to be stored
on the per-cpu lists") extends the PCP allocator to store THP pages, and
it determines whether to cache THP pages in PCP by comparing with
pageblock_order.  But the pageblock_order is not always equal to THP
order.  It might also be MAX_PAGE_ORDER, which could prevent PCP from
caching THP pages.

Therefore, using HPAGE_PMD_ORDER instead to determine the need for caching
THP for PCP will fix this issue

Link: https://lkml.kernel.org/r/a25c9e14cd03907d5978b60546a69e6aa3fc2a7d.1712151833.git.baolin.wang@linux.alibaba.com
Fixes: 44042b44 ("mm/page_alloc: allow high-order pages to be stored on the per-cpu lists")
Signed-off-by: Baolin Wang <baolin.wang@linux.alibaba.com>
Acked-by: Vlastimil Babka <vbabka@suse.cz>
Cc: Mel Gorman <mgorman@techsingularity.net>
Reviewed-by: Barry Song <baohua@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

mm/page_alloc.c

@@ -506,7 +506,7 @@ static inline unsigned int order_to_pindex(int migratetype, int order)
 {
 #ifdef CONFIG_TRANSPARENT_HUGEPAGE
 	if (order > PAGE_ALLOC_COSTLY_ORDER) {
-		VM_BUG_ON(order != pageblock_order);
+		VM_BUG_ON(order != HPAGE_PMD_ORDER);
 		return NR_LOWORDER_PCP_LISTS;
 	}
 #else
@@ -522,7 +522,7 @@ static inline int pindex_to_order(unsigned int pindex)
 
 #ifdef CONFIG_TRANSPARENT_HUGEPAGE
 	if (pindex == NR_LOWORDER_PCP_LISTS)
-		order = pageblock_order;
+		order = HPAGE_PMD_ORDER;
 #else
 	VM_BUG_ON(order > PAGE_ALLOC_COSTLY_ORDER);
 #endif
@@ -535,7 +535,7 @@ static inline bool pcp_allowed_order(unsigned int order)
 	if (order <= PAGE_ALLOC_COSTLY_ORDER)
 		return true;
 #ifdef CONFIG_TRANSPARENT_HUGEPAGE
-	if (order == pageblock_order)
+	if (order == HPAGE_PMD_ORDER)
 		return true;
 #endif
 	return false;