[PATCH v3] mm/memory-hotplug: fix lowmem count overflow when offline pages

[PATCH v3] mm/memory-hotplug: fix lowmem count overflow when offline pages

[Wanpeng Li]

Changelog:
 v1 -> v2:
	* show number of HighTotal before hotremove 
	* remove CONFIG_HIGHMEM
	* cc stable kernels
	* add Michal reviewed-by
 v2 -> v3:
    * correct way to request changes for stable

Logic memory-remove code fails to correctly account the Total High Memory 
when a memory block which contains High Memory is offlined as shown in the
example below. The following patch fixes it.

Before logic memory remove:

MemTotal:        7603740 kB
MemFree:         6329612 kB
Buffers:           94352 kB
Cached:           872008 kB
SwapCached:            0 kB
Active:           626932 kB
Inactive:         519216 kB
Active(anon):     180776 kB
Inactive(anon):   222944 kB
Active(file):     446156 kB
Inactive(file):   296272 kB
Unevictable:           0 kB
Mlocked:               0 kB
HighTotal:       7294672 kB
HighFree:        5704696 kB
LowTotal:         309068 kB
LowFree:          624916 kB

After logic memory remove:

MemTotal:        7079452 kB
MemFree:         5805976 kB
Buffers:           94372 kB
Cached:           872000 kB
SwapCached:            0 kB
Active:           626936 kB
Inactive:         519236 kB
Active(anon):     180780 kB
Inactive(anon):   222944 kB
Active(file):     446156 kB
Inactive(file):   296292 kB
Unevictable:           0 kB
Mlocked:               0 kB
HighTotal:       7294672 kB
HighFree:        5181024 kB
LowTotal:       4294752076 kB
LowFree:          624952 kB

Cc: <stable@vger.kernel.org> # 2.6.24 
Reviewed-by: Michal Hocko <mhocko@suse.cz>
Signed-off-by: Wanpeng Li <liwanp@linux.vnet.ibm.com>
---
 mm/page_alloc.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 98cbdf6..23b921f 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -6140,6 +6140,8 @@ __offline_isolated_pages(unsigned long start_pfn, unsigned long end_pfn)
 		list_del(&page->lru);
 		rmv_page_order(page);
 		zone->free_area[order].nr_free--;
+		if (PageHighMem(page))
+			totalhigh_pages -= 1 << order;
 		for (i = 0; i < (1 << order); i++)
 			SetPageReserved((page+i));
 		pfn += (1 << order);
-- 
1.8.1.2