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

Yasuaki Ishimatsu <isimatu.yasuaki@xxxxxxxxxxxxxx> · Thu, 28 Jun 2012 15:51:52 +0900

Hi Kosaki-san,

2012/06/28 14:26, KOSAKI Motohiro wrote:

On Wed, Jun 27, 2012 at 1:44 AM, Yasuaki Ishimatsu
<isimatu.yasuaki@xxxxxxxxxxxxxx> wrote:

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().


I don't understand your point. I think following misoperation should
fail. Otherwise
administrator have no way to know their fault.

$ echo offline > memoryN/state
$ echo offline > memoryN/state

In general, we don't like to ignore an error except the standard require it.


I understood the intention of previous mail (why the caller can't check it? ).
I'll move memory_is_offline() to caller side.



CC: Len Brown <len.brown@xxxxxxxxx>
CC: Benjamin Herrenschmidt <benh@xxxxxxxxxxxxxxxxxxx>
CC: Paul Mackerras <paulus@xxxxxxxxx>
CC: Christoph Lameter <cl@xxxxxxxxx>
Cc: Minchan Kim <minchan.kim@xxxxxxxxx>
CC: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
CC: KOSAKI Motohiro <kosaki.motohiro@xxxxxxxxxxxxxx>
CC: Wen Congyang <wency@xxxxxxxxxxxxxx>
Signed-off-by: Yasuaki Ishimatsu <isimatu.yasuaki@xxxxxxxxxxxxxx>

---
  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)


I dislike this function name. 'memory' is too vague to me.


O.K.
I retry to change the name of the function.





+{
+       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);


This seems to have strong sparse dependency.


Thanks.
I will consider other CONFIG_.

Thanks.
Yasuaki Ishimatsu


Hm, I wonder why memory-hotplug.c can enable when X86_64_ACPI_NUMA.

# eventually, we can have this option just 'select SPARSEMEM'
config MEMORY_HOTPLUG
	bool "Allow for memory hot-add"
	depends on SPARSEMEM || X86_64_ACPI_NUMA



+               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;

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