mm/memory_hotplug: optimize probe routine

When memory is hotplugged pages_correctly_reserved() is called to verify
that the added memory is present, this routine traverses through every
struct page and verifies that PageReserved() is set.  This is a slow
operation especially if a large amount of memory is added.

Instead of checking every page, it is enough to simply check that the
section is present, has mapping (struct page array is allocated), and
the mapping is online.

In addition, we should not excpect that probe routine sets flags in
struct page, as the struct pages have not yet been initialized.  The
initialization should be done in __init_single_page(), the same as
during boot.

Link: http://lkml.kernel.org/r/[email protected]
Signed-off-by: Pavel Tatashin <[email protected]>
Acked-by: Michal Hocko <[email protected]>
Cc: Ingo Molnar <[email protected]>
Cc: Baoquan He <[email protected]>
Cc: Bharata B Rao <[email protected]>
Cc: Daniel Jordan <[email protected]>
Cc: Dan Williams <[email protected]>
Cc: Greg Kroah-Hartman <[email protected]>
Cc: "H. Peter Anvin" <[email protected]>
Cc: Kirill A. Shutemov <[email protected]>
Cc: Mel Gorman <[email protected]>
Cc: Steven Sistare <[email protected]>
Cc: Thomas Gleixner <[email protected]>
Cc: Vlastimil Babka <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>

Author: Pavel Tatashin

drivers/base/memory.c

@@ -187,35 +187,39 @@ int memory_isolate_notify(unsigned long val, void *v)
 }
 
 /*
- * The probe routines leave the pages reserved, just as the bootmem code does.
- * Make sure they're still that way.
+ * The probe routines leave the pages uninitialized, just as the bootmem code
+ * does. Make sure we do not access them, but instead use only information from
+ * within sections.
  */
-static bool pages_correctly_reserved(unsigned long start_pfn)
+static bool pages_correctly_probed(unsigned long start_pfn)
 {
-	int i, j;
-	struct page *page;
+	unsigned long section_nr = pfn_to_section_nr(start_pfn);
+	unsigned long section_nr_end = section_nr + sections_per_block;
 	unsigned long pfn = start_pfn;
 
 	/*
 	 * memmap between sections is not contiguous except with
 	 * SPARSEMEM_VMEMMAP. We lookup the page once per section
 	 * and assume memmap is contiguous within each section
 	 */
-	for (i = 0; i < sections_per_block; i++, pfn += PAGES_PER_SECTION) {
+	for (; section_nr < section_nr_end; section_nr++) {
 		if (WARN_ON_ONCE(!pfn_valid(pfn)))
 			return false;
-		page = pfn_to_page(pfn);
-
-		for (j = 0; j < PAGES_PER_SECTION; j++) {
-			if (PageReserved(page + j))
-				continue;
-
-			printk(KERN_WARNING "section number %ld page number %d "
-				"not reserved, was it already online?\n",
-				pfn_to_section_nr(pfn), j);
 
+		if (!present_section_nr(section_nr)) {
+			pr_warn("section %ld pfn[%lx, %lx) not present",
+				section_nr, pfn, pfn + PAGES_PER_SECTION);
+			return false;
+		} else if (!valid_section_nr(section_nr)) {
+			pr_warn("section %ld pfn[%lx, %lx) no valid memmap",
+				section_nr, pfn, pfn + PAGES_PER_SECTION);
+			return false;
+		} else if (online_section_nr(section_nr)) {
+			pr_warn("section %ld pfn[%lx, %lx) is already online",
+				section_nr, pfn, pfn + PAGES_PER_SECTION);
 			return false;
 		}
+		pfn += PAGES_PER_SECTION;
 	}
 
 	return true;
@@ -237,7 +241,7 @@ memory_block_action(unsigned long phys_index, unsigned long action, int online_t
 
 	switch (action) {
 	case MEM_ONLINE:
-		if (!pages_correctly_reserved(start_pfn))
+		if (!pages_correctly_probed(start_pfn))
 			return -EBUSY;
 
 		ret = online_pages(start_pfn, nr_pages, online_type);