We use __free_page() to put a page to buddy system when onlining pages.
__free_page() will store NR_FREE_PAGES in zone's pcp.vm_stat_diff, so we
should allocate zone's pcp before onlining pages, otherwise we will lose
some free pages.

Cc: David Rientjes <[email protected]>
Cc: Jiang Liu <[email protected]>
Cc: Len Brown <[email protected]>
Cc: Benjamin Herrenschmidt <[email protected]>
Cc: Paul Mackerras <[email protected]>
Cc: Christoph Lameter <[email protected]>
Cc: Minchan Kim <[email protected]>
Cc: KOSAKI Motohiro <[email protected]>
Cc: Yasuaki Ishimatsu <[email protected]>
Cc: Dave Hansen <[email protected]>
Cc: Mel Gorman <[email protected]>
Signed-off-by: Wen Congyang <[email protected]>
---
 mm/memory_hotplug.c | 8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
index 72f4fef..63ea7df 100644
--- a/mm/memory_hotplug.c
+++ b/mm/memory_hotplug.c
@@ -505,12 +505,16 @@ int __ref online_pages(unsigned long pfn, unsigned long 
nr_pages)
         * So, zonelist must be updated after online.
         */
        mutex_lock(&zonelists_mutex);
-       if (!populated_zone(zone))
+       if (!populated_zone(zone)) {
                need_zonelists_rebuild = 1;
+               build_all_zonelists(NULL, zone);
+       }
 
        ret = walk_system_ram_range(pfn, nr_pages, &onlined_pages,
                online_pages_range);
        if (ret) {
+               if (need_zonelists_rebuild)
+                       zone_pcp_reset(zone);
                mutex_unlock(&zonelists_mutex);
                printk(KERN_DEBUG "online_pages [mem %#010llx-%#010llx] 
failed\n",
                       (unsigned long long) pfn << PAGE_SHIFT,
@@ -526,7 +530,7 @@ int __ref online_pages(unsigned long pfn, unsigned long 
nr_pages)
        if (onlined_pages) {
                node_set_state(zone_to_nid(zone), N_HIGH_MEMORY);
                if (need_zonelists_rebuild)
-                       build_all_zonelists(NULL, zone);
+                       build_all_zonelists(NULL, NULL);
                else
                        zone_pcp_update(zone);
        }
-- 
1.8.0

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