Re: [PATCH v3 06/12] memory-hotplug: unregister memory section on SPARSEMEM_VMEMMAP

At 11/20/2012 02:58 PM, Jaegeuk Hanse Wrote:

On 11/20/2012 02:55 PM, Wen Congyang wrote:

quoted

At 11/20/2012 02:22 PM, Jaegeuk Hanse Wrote:

quoted

On 11/01/2012 05:44 PM, Wen Congyang wrote:

quoted

From: Yasuaki Ishimatsu <redacted>

Currently __remove_section for SPARSEMEM_VMEMMAP does nothing. But
even if
we use SPARSEMEM_VMEMMAP, we can unregister the memory_section.

So the patch add unregister_memory_section() into __remove_section().

Hi Yasuaki,

In order to review this patch, I should dig sparse memory codes in
advance. But I have some confuse of codes. Why need encode/decode mem
map instead of set mem_map to ms->section_mem_map directly?

The memmap is aligned, and the low bits are zero. We store some
information
in these bits. So we need to encode/decode memmap here.

Hi Congyang,

Thanks for you reponse. But I mean why return (unsigned long)(mem_map -
(section_nr_to_pfn(pnum))); in function sparse_encode_mem_map, and then
return ((struct page *)coded_mem_map) + section_nr_to_pfn(pnum); in
funtion sparse_decode_mem_map instead of just store mem_map in
ms->section_mep_map directly.

I don't know why. I try to find the reason, but I don't find any
place to use the pfn stored in the mem_map except in the decode
function. Maybe the designer doesn't want us to access the mem_map
directly.

Thanks
Wen Congyang

Regards,
Jaegeuk

quoted

Thanks
Wen Congyang

quoted

Regards,
Jaegeuk

quoted

CC: David Rientjes <rientjes@google.com>
CC: Jiang Liu <redacted>
CC: Len Brown <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>
---
   mm/memory_hotplug.c | 13 ++++++++-----
   1 file changed, 8 insertions(+), 5 deletions(-)

diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
index ca07433..66a79a7 100644
--- a/mm/memory_hotplug.c
+++ b/mm/memory_hotplug.c

@@ -286,11 +286,14 @@ static int __meminit __add_section(int nid,

struct zone *zone,
   #ifdef CONFIG_SPARSEMEM_VMEMMAP
   static int __remove_section(struct zone *zone, struct mem_section
*ms)
   {
-    /*
-     * XXX: Freeing memmap with vmemmap is not implement yet.
-     *      This should be removed later.
-     */
-    return -EBUSY;
+    int ret = -EINVAL;
+
+    if (!valid_section(ms))
+        return ret;
+
+    ret = unregister_memory_section(ms);
+
+    return ret;
   }
   #else
   static int __remove_section(struct zone *zone, struct mem_section
*ms)