[PATCH v2 1/7] mm: factor zone-device page init helpers out of __init_zone_device_page

["Li Zhe" <lizhe.67@bytedance.com>]

memmap_init_zone_device() currently mixes refcount policy, core
ZONE_DEVICE page setup, and pageblock metadata handling in a single
helper.

Factor the refcount policy into zone_device_page_init_refcount(), move
the common page initialization into __zone_device_page_init(), split
pageblock handling into zone_device_page_init_pageblock(), and wrap the
existing slow path in zone_device_page_init_slow().

This keeps the slow-path behaviour unchanged and gives later patches
reusable helper boundaries.

No functional change intended.

Signed-off-by: Li Zhe <lizhe.67@bytedance.com>
---
 mm/mm_init.c | 64 +++++++++++++++++++++++++++++++++-------------------
 1 file changed, 41 insertions(+), 23 deletions(-)

diff --git a/mm/mm_init.c b/mm/mm_init.c
index f9f8e1af921c..4ba506df93bc 100644
--- a/mm/mm_init.c
+++ b/mm/mm_init.c
@@ -987,11 +987,36 @@ static void __init memmap_init(void)
 }
 
 #ifdef CONFIG_ZONE_DEVICE
-static void __ref __init_zone_device_page(struct page *page, unsigned long pfn,
+static inline int zone_device_page_init_refcount(
+		const struct dev_pagemap *pgmap)
+{
+	/*
+	 * ZONE_DEVICE pages other than MEMORY_TYPE_GENERIC are released
+	 * directly to the driver page allocator which will set the page count
+	 * to 1 when allocating the page.
+	 *
+	 * MEMORY_TYPE_GENERIC and MEMORY_TYPE_FS_DAX pages automatically have
+	 * their refcount reset to one whenever they are freed (ie. after
+	 * their refcount drops to 0).
+	 */
+	switch (pgmap->type) {
+	case MEMORY_DEVICE_FS_DAX:
+	case MEMORY_DEVICE_PRIVATE:
+	case MEMORY_DEVICE_COHERENT:
+	case MEMORY_DEVICE_PCI_P2PDMA:
+		return 0;
+	case MEMORY_DEVICE_GENERIC:
+		return 1;
+	default:
+		WARN_ONCE(1, "Unknown memory type!");
+		return 1;
+	}
+}
+
+static void __ref __zone_device_page_init(struct page *page, unsigned long pfn,
 					  unsigned long zone_idx, int nid,
 					  struct dev_pagemap *pgmap)
 {
-
 	__init_single_page(page, pfn, zone_idx, nid);
 
 	/*
@@ -1010,7 +1035,11 @@ static void __ref __init_zone_device_page(struct page *page, unsigned long pfn,
 	 */
 	page_folio(page)->pgmap = pgmap;
 	page->zone_device_data = NULL;
+}
 
+static void __ref zone_device_page_init_pageblock(struct page *page,
+						  unsigned long pfn)
+{
 	/*
 	 * Mark the block movable so that blocks are reserved for
 	 * movable at startup. This will force kernel allocations
@@ -1025,27 +1054,16 @@ static void __ref __init_zone_device_page(struct page *page, unsigned long pfn,
 		init_pageblock_migratetype(page, MIGRATE_MOVABLE, false);
 		cond_resched();
 	}
+}
 
-	/*
-	 * ZONE_DEVICE pages other than MEMORY_TYPE_GENERIC are released
-	 * directly to the driver page allocator which will set the page count
-	 * to 1 when allocating the page.
-	 *
-	 * MEMORY_TYPE_GENERIC and MEMORY_TYPE_FS_DAX pages automatically have
-	 * their refcount reset to one whenever they are freed (ie. after
-	 * their refcount drops to 0).
-	 */
-	switch (pgmap->type) {
-	case MEMORY_DEVICE_FS_DAX:
-	case MEMORY_DEVICE_PRIVATE:
-	case MEMORY_DEVICE_COHERENT:
-	case MEMORY_DEVICE_PCI_P2PDMA:
+static void __ref zone_device_page_init_slow(struct page *page,
+		unsigned long pfn, unsigned long zone_idx, int nid,
+		struct dev_pagemap *pgmap)
+{
+	__zone_device_page_init(page, pfn, zone_idx, nid, pgmap);
+	if (!zone_device_page_init_refcount(pgmap))
 		set_page_count(page, 0);
-		break;
-
-	case MEMORY_DEVICE_GENERIC:
-		break;
-	}
+	zone_device_page_init_pageblock(page, pfn);
 }
 
 /*
@@ -1084,7 +1102,7 @@ static void __ref memmap_init_compound(struct page *head,
 	for (pfn = head_pfn + 1; pfn < end_pfn; pfn++) {
 		struct page *page = pfn_to_page(pfn);
 
-		__init_zone_device_page(page, pfn, zone_idx, nid, pgmap);
+		zone_device_page_init_slow(page, pfn, zone_idx, nid, pgmap);
 		prep_compound_tail(page, head, order);
 		set_page_count(page, 0);
 	}
@@ -1120,7 +1138,7 @@ void __ref memmap_init_zone_device(struct zone *zone,
 	for (pfn = start_pfn; pfn < end_pfn; pfn += pfns_per_compound) {
 		struct page *page = pfn_to_page(pfn);
 
-		__init_zone_device_page(page, pfn, zone_idx, nid, pgmap);
+		zone_device_page_init_slow(page, pfn, zone_idx, nid, pgmap);
 
 		if (pfns_per_compound == 1)
 			continue;
-- 
2.20.1