Subject: [RFC PATCH v5 05/19] memory-hotplug: check whether memory is present or not

From: Wen Congyang <[email-masked]>
Date: Fri, 27 Jul 2012 18:28:20 +0800

From: Yasuaki Ishimatsu <[email-masked]>

If system supports memory hot-remove, online_pages() may online removed pages.
So online_pages() need to check whether onlining pages are present or not.

CC: David Rientjes <[email-masked]>
CC: Jiang Liu <[email-masked]>
CC: Len Brown <[email-masked]>
CC: Benjamin Herrenschmidt <[email-masked]>
CC: Paul Mackerras <[email-masked]>
CC: Christoph Lameter <[email-masked]>
Cc: Minchan Kim <[email-masked]>
CC: Andrew Morton <[email-masked]>
CC: KOSAKI Motohiro <[email-masked]>
CC: Wen Congyang <[email-masked]>
Signed-off-by: Yasuaki Ishimatsu <[email-masked]>
---
 include/linux/mmzone.h |   19 +++++++++++++++++++
 mm/memory_hotplug.c    |   13 +++++++++++++
 2 files changed, 32 insertions(+), 0 deletions(-)

diff --git a/include/linux/mmzone.h b/include/linux/mmzone.h
index 458988b..822f705 100644
--- a/include/linux/mmzone.h
+++ b/include/linux/mmzone.h
@@ -1168,6 +1168,25 @@ void sparse_init(void);
 #define sparse_index_init(_sec, _nid)  do {} while (0)
 #endif /* CONFIG_SPARSEMEM */
 
+#ifdef CONFIG_SPARSEMEM
+static inline int pfns_present(unsigned long pfn, unsigned long nr_pages)
+{
+	int i;
+	for (i = 0; i < nr_pages; i++) {
+		if (pfn_present(pfn + 1))
+			continue;
+		else
+			return -EINVAL;
+	}
+	return 0;
+}
+#else
+static inline int pfns_present(unsigned long pfn, unsigned long nr_pages)
+{
+	return 0;
+}
+#endif /* CONFIG_SPARSEMEM*/
+
 #ifdef CONFIG_NODES_SPAN_OTHER_NODES
 bool early_pfn_in_nid(unsigned long pfn, int nid);
 #else
diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
index 5af0a9f..d510be0 100644
--- a/mm/memory_hotplug.c
+++ b/mm/memory_hotplug.c
@@ -467,6 +467,19 @@ int __ref online_pages(unsigned long pfn, unsigned long nr_pages)
 	struct memory_notify arg;
 
 	lock_memory_hotplug();
+	/*
+	 * If system supports memory hot-remove, the memory may have been
+	 * removed. So we check whether the memory has been removed or not.
+	 *
+	 * Note: When CONFIG_SPARSEMEM is defined, pfns_present() become
+	 *       effective. If CONFIG_SPARSEMEM is not defined, pfns_present()
+	 *       always returns 0.
+	 */
+	ret = pfns_present(pfn, nr_pages);
+	if (ret) {
+		unlock_memory_hotplug();
+		return ret;
+	}
 	arg.start_pfn = pfn;
 	arg.nr_pages = nr_pages;
 	arg.status_change_nid = -1;
-- 
1.7.1