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SubjectRe: node-hotplug: is memset 0 safe in try_offline_node()?
On 2015/3/5 16:26, Gu Zheng wrote:

> Hi Xishi,
> Could you please try the following one?
> It postpones the reset of obsolete pgdat from try_offline_node() to
> hotadd_new_pgdat(), and just resetting pgdat->nr_zones and
> pgdat->classzone_idx to be 0 rather than the whole reset by memset()
> as Kame suggested.
>
> Regards,
> Gu
>
> ---
> mm/memory_hotplug.c | 13 ++++---------
> 1 files changed, 4 insertions(+), 9 deletions(-)
>
> diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
> index 1778628..c17eebf 100644
> --- a/mm/memory_hotplug.c
> +++ b/mm/memory_hotplug.c
> @@ -1092,6 +1092,10 @@ static pg_data_t __ref *hotadd_new_pgdat(int nid, u64 start)
> return NULL;
>
> arch_refresh_nodedata(nid, pgdat);
> + } else {
> + /* Reset the nr_zones and classzone_idx to 0 before reuse */
> + pgdat->nr_zones = 0;
> + pgdat->classzone_idx = 0;

Hi Gu,

This is just to avoid the warning, I think it's no meaning.
Here is the changlog from the original patch:

commit 88fdf75d1bb51d85ba00c466391770056d44bc03
...
Warn if memory-hotplug/boot code doesn't initialize pg_data_t with zero
when it is allocated. Arch code and memory hotplug already initiailize
pg_data_t. So this warning should never happen. I select fields *randomly*
near the beginning, middle and end of pg_data_t for checking.
...

Thanks,
Xishi Qiu

> }
>
> /* we can use NODE_DATA(nid) from here */
> @@ -2021,15 +2025,6 @@ void try_offline_node(int nid)
>
> /* notify that the node is down */
> call_node_notify(NODE_DOWN, (void *)(long)nid);
> -
> - /*
> - * Since there is no way to guarentee the address of pgdat/zone is not
> - * on stack of any kernel threads or used by other kernel objects
> - * without reference counting or other symchronizing method, do not
> - * reset node_data and free pgdat here. Just reset it to 0 and reuse
> - * the memory when the node is online again.
> - */
> - memset(pgdat, 0, sizeof(*pgdat));
> }
> EXPORT_SYMBOL(try_offline_node);
>





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