mm/page_alloc: simplify __offline_isolated_pages()

offline_pages() is the only user.  __offline_isolated_pages() never gets
called with ranges that contain memory holes and we no longer care about
the return value.  Drop the return value handling and all pfn_valid()
checks.

Update the documentation.
Signed-off-by: David Hildenbrand <david@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Reviewed-by: Oscar Salvador <osalvador@suse.de>
Acked-by: Michal Hocko <mhocko@suse.com>
Cc: Wei Yang <richard.weiyang@linux.alibaba.com>
Cc: Baoquan He <bhe@redhat.com>
Cc: Pankaj Gupta <pankaj.gupta.linux@gmail.com>
Cc: Charan Teja Reddy <charante@codeaurora.org>
Cc: Dan Williams <dan.j.williams@intel.com>
Cc: Fenghua Yu <fenghua.yu@intel.com>
Cc: Logan Gunthorpe <logang@deltatee.com>
Cc: "Matthew Wilcox (Oracle)" <willy@infradead.org>
Cc: Mel Gorman <mgorman@suse.de>
Cc: Mel Gorman <mgorman@techsingularity.net>
Cc: Michel Lespinasse <walken@google.com>
Cc: Mike Rapoport <rppt@kernel.org>
Cc: Tony Luck <tony.luck@intel.com>
Link: https://lkml.kernel.org/r/20200819175957.28465-5-david@redhat.comSigned-off-by: Linus Torvalds <torvalds@linux-foundation.org>

include/linux/memory_hotplug.h

@@ -103,7 +103,7 @@ extern int online_pages(unsigned long pfn, unsigned long nr_pages,
 			int online_type, int nid);
 extern struct zone *test_pages_in_a_zone(unsigned long start_pfn,
 					 unsigned long end_pfn);
-extern unsigned long __offline_isolated_pages(unsigned long start_pfn,
+extern void __offline_isolated_pages(unsigned long start_pfn,
 				     unsigned long end_pfn);
 
 typedef void (*online_page_callback_t)(struct page *page, unsigned int order);

mm/page_alloc.c

@@ -8704,35 +8704,21 @@ void zone_pcp_reset(struct zone *zone)
 
 #ifdef CONFIG_MEMORY_HOTREMOVE
 /*
- * All pages in the range must be in a single zone and isolated
- * before calling this.
+ * All pages in the range must be in a single zone, must not contain holes,
+ * must span full sections, and must be isolated before calling this function.
  */
-unsigned long
-__offline_isolated_pages(unsigned long start_pfn, unsigned long end_pfn)
+void __offline_isolated_pages(unsigned long start_pfn, unsigned long end_pfn)
 {
+	unsigned long pfn = start_pfn;
 	struct page *page;
 	struct zone *zone;
 	unsigned int order;
-	unsigned long pfn;
 	unsigned long flags;
-	unsigned long offlined_pages = 0;
-
-	/* find the first valid pfn */
-	for (pfn = start_pfn; pfn < end_pfn; pfn++)
-		if (pfn_valid(pfn))
-			break;
-	if (pfn == end_pfn)
-		return offlined_pages;
 
 	offline_mem_sections(pfn, end_pfn);
 	zone = page_zone(pfn_to_page(pfn));
 	spin_lock_irqsave(&zone->lock, flags);
-	pfn = start_pfn;
 	while (pfn < end_pfn) {
-		if (!pfn_valid(pfn)) {
-			pfn++;
-			continue;
-		}
 		page = pfn_to_page(pfn);
 		/*
 		 * The HWPoisoned page may be not in buddy system, and
@@ -8740,7 +8726,6 @@ __offline_isolated_pages(unsigned long start_pfn, unsigned long end_pfn)
 		 */
 		if (unlikely(!PageBuddy(page) && PageHWPoison(page))) {
 			pfn++;
-			offlined_pages++;
 			continue;
 		}
 		/*
@@ -8751,20 +8736,16 @@ __offline_isolated_pages(unsigned long start_pfn, unsigned long end_pfn)
 			BUG_ON(page_count(page));
 			BUG_ON(PageBuddy(page));
 			pfn++;
-			offlined_pages++;
 			continue;
 		}
 
 		BUG_ON(page_count(page));
 		BUG_ON(!PageBuddy(page));
 		order = page_order(page);
-		offlined_pages += 1 << order;
 		del_page_from_free_list(page, zone, order);
 		pfn += (1 << order);
 	}
 	spin_unlock_irqrestore(&zone->lock, flags);
-
-	return offlined_pages;
 }
 #endif