---

yaml
---
r: 343341
b: refs/heads/master
c: 01cefae
h: refs/heads/master
i:
  343339: 70bb9ec
v: v3

[refs]

@@ -1,2 +1,2 @@
 ---
-refs/heads/master: 02c0ab684fc41bc13ba8d5ad89b0dc73b092fa08
+refs/heads/master: 01cefaef40c48c714b7476e62781230993e10dbf

trunk/mm/page_alloc.c

@@ -4489,6 +4489,26 @@ void __init set_pageblock_order(void)
 
 #endif /* CONFIG_HUGETLB_PAGE_SIZE_VARIABLE */
 
+static unsigned long __paginginit calc_memmap_size(unsigned long spanned_pages,
+						   unsigned long present_pages)
+{
+	unsigned long pages = spanned_pages;
+
+	/*
+	 * Provide a more accurate estimation if there are holes within
+	 * the zone and SPARSEMEM is in use. If there are holes within the
+	 * zone, each populated memory region may cost us one or two extra
+	 * memmap pages due to alignment because memmap pages for each
+	 * populated regions may not naturally algined on page boundary.
+	 * So the (present_pages >> 4) heuristic is a tradeoff for that.
+	 */
+	if (spanned_pages > present_pages + (present_pages >> 4) &&
+	    IS_ENABLED(CONFIG_SPARSEMEM))
+		pages = present_pages;
+
+	return PAGE_ALIGN(pages * sizeof(struct page)) >> PAGE_SHIFT;
+}
+
 /*
  * Set up the zone data structures:
  *   - mark all pages reserved
@@ -4523,8 +4543,7 @@ static void __paginginit free_area_init_core(struct pglist_data *pgdat,
 		 * is used by this zone for memmap. This affects the watermark
 		 * and per-cpu initialisations
 		 */
-		memmap_pages =
-			PAGE_ALIGN(size * sizeof(struct page)) >> PAGE_SHIFT;
+		memmap_pages = calc_memmap_size(size, realsize);
 		if (freesize >= memmap_pages) {
 			freesize -= memmap_pages;
 			if (memmap_pages)
@@ -4545,6 +4564,9 @@ static void __paginginit free_area_init_core(struct pglist_data *pgdat,
 
 		if (!is_highmem_idx(j))
 			nr_kernel_pages += freesize;
+		/* Charge for highmem memmap if there are enough kernel pages */
+		else if (nr_kernel_pages > memmap_pages * 2)
+			nr_kernel_pages -= memmap_pages;
 		nr_all_pages += freesize;
 
 		zone->spanned_pages = size;