[PATCH rfc 1/3] mm: prepare more high-order pages to be stored on the per-cpu lists

[Kefeng Wang <wangkefeng.wang@huawei.com>]

Both the file pages and anonymous pages support large folio, high-order
pages except HPAGE_PMD_ORDER(PMD_SHIFT - PAGE_SHIFT) will be allocated
frequently which will increase the zone lock contention, allow high-order
pages on pcp lists could alleviate the big zone lock contention, in order
to allows high-orders(PAGE_ALLOC_COSTLY_ORDER, HPAGE_PMD_ORDER) to be
stored on the per-cpu lists, similar with PMD_ORDER pages, more lists is
added in struct per_cpu_pages (one list each high-order pages), also a
new PCP_MAX_ORDER instead of HPAGE_PMD_ORDER is added in mmzone.h.

But as commit 44042b449872 ("mm/page_alloc: allow high-order pages to be
stored on the per-cpu lists") pointed, it may not win in all the scenes,
so this don't allow higher-order pages to be added to PCP list, the next
will add a control to enable or disable it.

The struct per_cpu_pages increases in size from 256(4 cache lines) to
320 bytes (5 cache lines) on arm64 with defconfig.

Signed-off-by: Kefeng Wang <wangkefeng.wang@huawei.com>
---
 include/linux/mmzone.h |  4 +++-
 mm/page_alloc.c        | 10 +++++-----
 2 files changed, 8 insertions(+), 6 deletions(-)

diff --git a/include/linux/mmzone.h b/include/linux/mmzone.h
index c11b7cde81ef..c745e2f1a0f2 100644
--- a/include/linux/mmzone.h
+++ b/include/linux/mmzone.h
@@ -657,11 +657,13 @@ enum zone_watermarks {
  * failures.
  */
 #ifdef CONFIG_TRANSPARENT_HUGEPAGE
-#define NR_PCP_THP 1
+#define PCP_MAX_ORDER (PMD_SHIFT - PAGE_SHIFT)
+#define NR_PCP_THP (PCP_MAX_ORDER - PAGE_ALLOC_COSTLY_ORDER)
 #else
 #define NR_PCP_THP 0
 #endif
 #define NR_LOWORDER_PCP_LISTS (MIGRATE_PCPTYPES * (PAGE_ALLOC_COSTLY_ORDER + 1))
+#define HIGHORDER_PCP_LIST_INDEX (NR_LOWORDER_PCP_LISTS - (PAGE_ALLOC_COSTLY_ORDER + 1))
 #define NR_PCP_LISTS (NR_LOWORDER_PCP_LISTS + NR_PCP_THP)
 
 #define min_wmark_pages(z) (z->_watermark[WMARK_MIN] + z->watermark_boost)
diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index b51becf03d1e..2248afc7b73a 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -506,8 +506,8 @@ 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 != HPAGE_PMD_ORDER);
-		return NR_LOWORDER_PCP_LISTS;
+		VM_BUG_ON(order > PCP_MAX_ORDER);
+		return order + HIGHORDER_PCP_LIST_INDEX;
 	}
 #else
 	VM_BUG_ON(order > PAGE_ALLOC_COSTLY_ORDER);
@@ -521,8 +521,8 @@ 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;
+	if (pindex >= NR_LOWORDER_PCP_LISTS)
+		order = pindex - HIGHORDER_PCP_LIST_INDEX;
 #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 == HPAGE_PMD_ORDER)
+	if (order == PCP_MAX_ORDER)
 		return true;
 #endif
 	return false;
-- 
2.27.0