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SubjectRe: [PATCH] mm/hotplug: prevent memory leak when reuse pgdat
On Tue 13-08-19 10:06:08, Wei Yang wrote:
> When offline a node in try_offline_node, pgdat is not released. So that
> pgdat could be reused in hotadd_new_pgdat. While we re-allocate
> pgdat->per_cpu_nodestats if this pgdat is reused.
>
> This patch prevents the memory leak by just allocate per_cpu_nodestats
> when it is a new pgdat.

Yes this makes sense! I was slightly confused why we haven't initialized
the allocated pcp area because __alloc_percpu does GFP_KERNEL without
__GFP_ZERO but then I've just found out that the zeroying is done
regardless. A bit unexpected...

> NOTE: This is not tested since I didn't manage to create a case to
> offline a whole node. If my analysis is not correct, please let me know.
>
> Signed-off-by: Wei Yang <richardw.yang@linux.intel.com>

Acked-by: Michal Hocko <mhocko@suse.com>

Thanks!

> ---
> mm/memory_hotplug.c | 10 +++++++++-
> 1 file changed, 9 insertions(+), 1 deletion(-)
>
> diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
> index c73f09913165..efaf9e6f580a 100644
> --- a/mm/memory_hotplug.c
> +++ b/mm/memory_hotplug.c
> @@ -933,8 +933,11 @@ static pg_data_t __ref *hotadd_new_pgdat(int nid, u64 start)
> if (!pgdat)
> return NULL;
>
> + pgdat->per_cpu_nodestats =
> + alloc_percpu(struct per_cpu_nodestat);
> arch_refresh_nodedata(nid, pgdat);
> } else {
> + int cpu;
> /*
> * Reset the nr_zones, order and classzone_idx before reuse.
> * Note that kswapd will init kswapd_classzone_idx properly
> @@ -943,6 +946,12 @@ static pg_data_t __ref *hotadd_new_pgdat(int nid, u64 start)
> pgdat->nr_zones = 0;
> pgdat->kswapd_order = 0;
> pgdat->kswapd_classzone_idx = 0;
> + for_each_online_cpu(cpu) {
> + struct per_cpu_nodestat *p;
> +
> + p = per_cpu_ptr(pgdat->per_cpu_nodestats, cpu);
> + memset(p, 0, sizeof(*p));
> + }
> }
>
> /* we can use NODE_DATA(nid) from here */
> @@ -952,7 +961,6 @@ static pg_data_t __ref *hotadd_new_pgdat(int nid, u64 start)
>
> /* init node's zones as empty zones, we don't have any present pages.*/
> free_area_init_core_hotplug(nid);
> - pgdat->per_cpu_nodestats = alloc_percpu(struct per_cpu_nodestat);
>
> /*
> * The node we allocated has no zone fallback lists. For avoiding
> --
> 2.17.1
>

--
Michal Hocko
SUSE Labs

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