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

@@ -6572,6 +6572,46 @@ void __meminit memmap_init_range(unsigned long size, int nid, unsigned long zone
 }
 
 #ifdef CONFIG_ZONE_DEVICE
+static void __ref __init_zone_device_page(struct page *page, unsigned long pfn,
+					  unsigned long zone_idx, int nid,
+					  struct dev_pagemap *pgmap)
+{
+
+	__init_single_page(page, pfn, zone_idx, nid);
+
+	/*
+	 * Mark page reserved as it will need to wait for onlining
+	 * phase for it to be fully associated with a zone.
+	 *
+	 * We can use the non-atomic __set_bit operation for setting
+	 * the flag as we are still initializing the pages.
+	 */
+	__SetPageReserved(page);
+
+	/*
+	 * ZONE_DEVICE pages union ->lru with a ->pgmap back pointer
+	 * and zone_device_data.  It is a bug if a ZONE_DEVICE page is
+	 * ever freed or placed on a driver-private list.
+	 */
+	page->pgmap = pgmap;
+	page->zone_device_data = NULL;
+
+	/*
+	 * Mark the block movable so that blocks are reserved for
+	 * movable at startup. This will force kernel allocations
+	 * to reserve their blocks rather than leaking throughout
+	 * the address space during boot when many long-lived
+	 * kernel allocations are made.
+	 *
+	 * Please note that MEMINIT_HOTPLUG path doesn't clear memmap
+	 * because this is done early in section_activate()
+	 */
+	if (IS_ALIGNED(pfn, pageblock_nr_pages)) {
+		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,
@@ -6600,39 +6640,7 @@ void __ref memmap_init_zone_device(struct zone *zone,
 	for (pfn = start_pfn; pfn < end_pfn; pfn++) {
 		struct page *page = pfn_to_page(pfn);
 
-		__init_single_page(page, pfn, zone_idx, nid);
-
-		/*
-		 * Mark page reserved as it will need to wait for onlining
-		 * phase for it to be fully associated with a zone.
-		 *
-		 * We can use the non-atomic __set_bit operation for setting
-		 * the flag as we are still initializing the pages.
-		 */
-		__SetPageReserved(page);
-
-		/*
-		 * ZONE_DEVICE pages union ->lru with a ->pgmap back pointer
-		 * and zone_device_data.  It is a bug if a ZONE_DEVICE page is
-		 * ever freed or placed on a driver-private list.
-		 */
-		page->pgmap = pgmap;
-		page->zone_device_data = NULL;
-
-		/*
-		 * Mark the block movable so that blocks are reserved for
-		 * movable at startup. This will force kernel allocations
-		 * to reserve their blocks rather than leaking throughout
-		 * the address space during boot when many long-lived
-		 * kernel allocations are made.
-		 *
-		 * Please note that MEMINIT_HOTPLUG path doesn't clear memmap
-		 * because this is done early in section_activate()
-		 */
-		if (IS_ALIGNED(pfn, pageblock_nr_pages)) {
-			set_pageblock_migratetype(page, MIGRATE_MOVABLE);
-			cond_resched();
-		}
+		__init_zone_device_page(page, pfn, zone_idx, nid, pgmap);
 	}
 
 	pr_info("%s initialised %lu pages in %ums\n", __func__,