On 09/11/2012 10:24 AM, Yasuaki Ishimatsu wrote:

Hi Wen,

2012/09/11 11:15, Wen Congyang wrote:

quoted

Hi, ishimatsu

At 09/05/2012 05:25 PM, wency@cn.fujitsu.com Wrote:

quoted

From: Yasuaki Ishimatsu <redacted>

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.

Because we use memory_block_change_state() to hotremoving memory, I 
think
this patch can be removed. What do you think?

Pleae teach me detals a little more. If we use 
memory_block_change_state(),
does the conflict never occur? Why?

since memory hot-add or hot-remove is based on memblock, if check in 
memory_block_change_state()
can guarantee conflict never occur?

Thansk,
Yasuaki Ishimatsu

quoted

Thanks
Wen Congyang

quoted

CC: David Rientjes <rientjes@google.com>
CC: Jiang Liu <redacted>
CC: Len Brown <redacted>
CC: Benjamin Herrenschmidt <benh@kernel.crashing.org>
CC: Paul Mackerras <redacted>
CC: Christoph Lameter <redacted>
Cc: Minchan Kim <redacted>
CC: Andrew Morton <akpm@linux-foundation.org>
CC: KOSAKI Motohiro <redacted>
CC: Wen Congyang <redacted>
Signed-off-by: Yasuaki Ishimatsu <redacted>
---
  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 2daa54f..ac3ae30 100644
--- a/include/linux/mmzone.h
+++ b/include/linux/mmzone.h

@@ -1180,6 +1180,25 @@ 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 + i))
+            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 49f7747..299747d 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;

-- 
To unsubscribe, send a message with 'unsubscribe linux-mm' in
the body to majordomo@kvack.org.  For more info on Linux MM,
see: http://www.linux-mm.org/ .
Don't email: <a href=mailto:"dont@kvack.org"> email@kvack.org </a>