Re: [PATCH v2 2/2] mem-hotplug: Reset node present pages when hot-adding a new pgdat.

[Yasuaki Ishimatsu <isimatu.yasuaki@jp.fujitsu.com>]

(2014/11/11 10:27), Tang Chen wrote:
> When onlining memory on node2, node2 zoneinfo and node3 meminfo corrupted:
> 
> # for ((i = 2048; i < 2064; i++)); do echo online_movable > /sys/devices/system/node/node2/memory$i/state; done
> # cat /sys/devices/system/node/node2/meminfo
> Node 2 MemTotal:       33554432 kB
> Node 2 MemFree:        33549092 kB
> Node 2 MemUsed:            5340 kB
> ......
> # cat /sys/devices/system/node/node3/meminfo
> Node 3 MemTotal:              0 kB
> Node 3 MemFree:               248 kB      /* corrupted, should be 0 */
> Node 3 MemUsed:               0 kB
> ......
> 
> # cat /proc/zoneinfo
> ......
> Node 2, zone   Movable
> ......
>          spanned  8388608
>          present  16777216               /* corrupted, should be 8388608 */
>          managed  8388608
> 
> 
> When memory is hot-added, all the memory is in offline state. So
> clear all zone->present_pages because they will be updated in
> online_pages() and offline_pages().
> 
> Signed-off-by: Tang Chen <tangchen@cn.fujitsu.com>

> Reviewed-by: Yasuaki Ishimatsu <isimatu.yasuaki@jp.fujitsu.com>

I has reviewed your patch. But I have one comment.
Please see below.

> ---
>   mm/memory_hotplug.c | 15 +++++++++++++++
>   1 file changed, 15 insertions(+)
> 
> diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
> index 8aba12b..26eac61 100644
> --- a/mm/memory_hotplug.c
> +++ b/mm/memory_hotplug.c
> @@ -1067,6 +1067,14 @@ out:
>   }
>   #endif /* CONFIG_MEMORY_HOTPLUG_SPARSE */
>   

> +static void reset_node_present_pages(pg_data_t *pgdat)
> +{
> +        struct zone *z;
> +
> +        for (z = pgdat->node_zones; z < pgdat->node_zones + MAX_NR_ZONES; z++)
> +                z->present_pages = 0;
> +}

You should reset pgdat->node_present_pages.
pgdat->node_present_pages is set to realtotalpages by calculate_node_totalpages().
And it is also incremented/decremented by memroy online/offline.
So pgdat->node_present_pages is broken internally too.

Thanks,
Yasuaki Ishimatsu.

> +
>   /* we are OK calling __meminit stuff here - we have CONFIG_MEMORY_HOTPLUG */
>   static pg_data_t __ref *hotadd_new_pgdat(int nid, u64 start)
>   {
> @@ -1105,6 +1113,13 @@ static pg_data_t __ref *hotadd_new_pgdat(int nid, u64 start)
>   	 */
>   	reset_node_managed_pages(pgdat);
>   
> +	/*
> +	 * When memory is hot-added, all the memory is in offline state. So
> +	 * clear all zones' present_pages because they will be updated in
> +	 * online_pages() and offline_pages().
> +	 */
> +	reset_node_present_pages(pgdat);
> +
>   	return pgdat;
>   }
>   
> 


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