mm/page_alloc: refactor memmap_init_zone_device() page init

Move struct page init to an helper function __init_zone_device_page().

This is in preparation for sharing the storage for compound page
metadata.

Link: https://lkml.kernel.org/r/20211202204422.26777-4-joao.m.martins@oracle.comSigned-off-by: Joao Martins <joao.m.martins@oracle.com>
Reviewed-by: Dan Williams <dan.j.williams@intel.com>
Cc: Christoph Hellwig <hch@lst.de>
Cc: Dave Jiang <dave.jiang@intel.com>
Cc: Jane Chu <jane.chu@oracle.com>
Cc: Jason Gunthorpe <jgg@nvidia.com>
Cc: Jason Gunthorpe <jgg@ziepe.ca>
Cc: John Hubbard <jhubbard@nvidia.com>
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: Matthew Wilcox (Oracle) <willy@infradead.org>
Cc: Mike Kravetz <mike.kravetz@oracle.com>
Cc: Muchun Song <songmuchun@bytedance.com>
Cc: Naoya Horiguchi <naoya.horiguchi@nec.com>
Cc: Vishal Verma <vishal.l.verma@intel.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

mm/page_alloc.c

@@ -6572,33 +6572,10 @@ void __meminit memmap_init_range(unsigned long size, int nid, unsigned long zone
 }
 
 #ifdef CONFIG_ZONE_DEVICE
-void __ref memmap_init_zone_device(struct zone *zone,
-				   unsigned long start_pfn,
-				   unsigned long nr_pages,
+static void __ref __init_zone_device_page(struct page *page, unsigned long pfn,
+					  unsigned long zone_idx, int nid,
 					  struct dev_pagemap *pgmap)
 {
-	unsigned long pfn, end_pfn = start_pfn + nr_pages;
-	struct pglist_data *pgdat = zone->zone_pgdat;
-	struct vmem_altmap *altmap = pgmap_altmap(pgmap);
-	unsigned long zone_idx = zone_idx(zone);
-	unsigned long start = jiffies;
-	int nid = pgdat->node_id;
-
-	if (WARN_ON_ONCE(!pgmap || zone_idx(zone) != ZONE_DEVICE))
-		return;
-
-	/*
-	 * The call to memmap_init should have already taken care
-	 * of the pages reserved for the memmap, so we can just jump to
-	 * the end of that region and start processing the device pages.
-	 */
-	if (altmap) {
-		start_pfn = altmap->base_pfn + vmem_altmap_offset(altmap);
-		nr_pages = end_pfn - start_pfn;
-	}
-
-	for (pfn = start_pfn; pfn < end_pfn; pfn++) {
-		struct page *page = pfn_to_page(pfn);
 
 	__init_single_page(page, pfn, zone_idx, nid);
 
@@ -6633,6 +6610,37 @@ void __ref memmap_init_zone_device(struct zone *zone,
 		set_pageblock_migratetype(page, MIGRATE_MOVABLE);
 		cond_resched();
 	}
+}
+
+void __ref memmap_init_zone_device(struct zone *zone,
+				   unsigned long start_pfn,
+				   unsigned long nr_pages,
+				   struct dev_pagemap *pgmap)
+{
+	unsigned long pfn, end_pfn = start_pfn + nr_pages;
+	struct pglist_data *pgdat = zone->zone_pgdat;
+	struct vmem_altmap *altmap = pgmap_altmap(pgmap);
+	unsigned long zone_idx = zone_idx(zone);
+	unsigned long start = jiffies;
+	int nid = pgdat->node_id;
+
+	if (WARN_ON_ONCE(!pgmap || zone_idx(zone) != ZONE_DEVICE))
+		return;
+
+	/*
+	 * The call to memmap_init should have already taken care
+	 * of the pages reserved for the memmap, so we can just jump to
+	 * the end of that region and start processing the device pages.
+	 */
+	if (altmap) {
+		start_pfn = altmap->base_pfn + vmem_altmap_offset(altmap);
+		nr_pages = end_pfn - start_pfn;
+	}
+
+	for (pfn = start_pfn; pfn < end_pfn; pfn++) {
+		struct page *page = pfn_to_page(pfn);
+
+		__init_zone_device_page(page, pfn, zone_idx, nid, pgmap);
 	}
 
 	pr_info("%s initialised %lu pages in %ums\n", __func__,