Re: [PATCH] mm/hotplug: prevent memory leak when reuse pgdat

[Wei Yang]

On Tue, Aug 13, 2019 at 09:57:07AM +0200, Michal Hocko wrote:
>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@xxxxxxxxxxxxxxx>
>
>Acked-by: Michal Hocko <mhocko@xxxxxxxx>
>
>Thanks!
>

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

-- 
Wei Yang
Help you, Help me