[RFC PATCH 2/12] memory-hogplug : check memory offline in offline_pages

[Yasuaki Ishimatsu]

When offline_pages() is called to offlined memory, the function fails since
all memory has been offlined. In this case, the function should succeed.
The patch adds the check function into offline_pages().

CC: Len Brown <len.brown at intel.com>
CC: Benjamin Herrenschmidt <benh at kernel.crashing.org>
CC: Paul Mackerras <paulus at samba.org>
CC: Christoph Lameter <cl at linux.com>
Cc: Minchan Kim <minchan.kim at gmail.com>
CC: Andrew Morton <akpm at linux-foundation.org>
CC: KOSAKI Motohiro <kosaki.motohiro at jp.fujitsu.com>
CC: Wen Congyang <wency at cn.fujitsu.com>
Signed-off-by: Yasuaki Ishimatsu <isimatu.yasuaki at jp.fujitsu.com>

---
 drivers/base/memory.c  |   20 ++++++++++++++++++++
 include/linux/memory.h |    1 +
 mm/memory_hotplug.c    |    5 +++++
 3 files changed, 26 insertions(+)

Index: linux-3.5-rc4/drivers/base/memory.c
===================================================================
--- linux-3.5-rc4.orig/drivers/base/memory.c	2012-06-26 13:28:16.726211752 +0900
+++ linux-3.5-rc4/drivers/base/memory.c	2012-06-26 13:34:22.423639904 +0900
@@ -70,6 +70,26 @@ void unregister_memory_isolate_notifier(
 }
 EXPORT_SYMBOL(unregister_memory_isolate_notifier);

+bool memory_is_offline(unsigned long start_pfn, unsigned long end_pfn)
+{
+	struct memory_block *mem;
+	struct mem_section *section;
+	unsigned long pfn, section_nr;
+
+	for (pfn = start_pfn; pfn < end_pfn; pfn += PAGES_PER_SECTION) {
+		section_nr = pfn_to_section_nr(pfn);
+		section = __nr_to_section(section_nr);
+		mem = find_memory_block(section);
+		if (!mem)
+			continue;
+		if (mem->state == MEM_OFFLINE)
+			continue;
+		return false;
+	}
+
+	return true;
+}
+
 /*
  * register_memory - Setup a sysfs device for a memory block
  */
Index: linux-3.5-rc4/include/linux/memory.h
===================================================================
--- linux-3.5-rc4.orig/include/linux/memory.h	2012-06-25 04:53:04.000000000 +0900
+++ linux-3.5-rc4/include/linux/memory.h	2012-06-26 13:34:22.424639891 +0900
@@ -120,6 +120,7 @@ extern int memory_isolate_notify(unsigne
 extern struct memory_block *find_memory_block_hinted(struct mem_section *,
 							struct memory_block *);
 extern struct memory_block *find_memory_block(struct mem_section *);
+extern bool memory_is_offline(unsigned long start_pfn, unsigned long end_pfn);
 #define CONFIG_MEM_BLOCK_SIZE	(PAGES_PER_SECTION<<PAGE_SHIFT)
 enum mem_add_context { BOOT, HOTPLUG };
 #endif /* CONFIG_MEMORY_HOTPLUG_SPARSE */
Index: linux-3.5-rc4/mm/memory_hotplug.c
===================================================================
--- linux-3.5-rc4.orig/mm/memory_hotplug.c	2012-06-26 13:28:16.743211538 +0900
+++ linux-3.5-rc4/mm/memory_hotplug.c	2012-06-26 13:48:38.264940468 +0900
@@ -887,6 +887,11 @@ static int __ref offline_pages(unsigned

 	lock_memory_hotplug();

+	if (memory_is_offline(start_pfn, end_pfn)) {
+		ret = 0;
+		goto out;
+	}
+
 	zone = page_zone(pfn_to_page(start_pfn));
 	node = zone_to_nid(zone);
 	nr_pages = end_pfn - start_pfn;