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* [PATCH] mm/hotplug: prevent memory leak when reuse pgdat
@ 2019-08-13  2:06 Wei Yang
  2019-08-13  7:57 ` Michal Hocko
  0 siblings, 1 reply; 3+ messages in thread
From: Wei Yang @ 2019-08-13  2:06 UTC (permalink / raw)
  To: akpm, osalvador, mhocko; +Cc: linux-mm, linux-kernel, Wei Yang

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.

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>
---
 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



^ permalink raw reply	[flat|nested] 3+ messages in thread

* Re: [PATCH] mm/hotplug: prevent memory leak when reuse pgdat
  2019-08-13  2:06 [PATCH] mm/hotplug: prevent memory leak when reuse pgdat Wei Yang
@ 2019-08-13  7:57 ` Michal Hocko
  2019-08-13 13:13   ` Wei Yang
  0 siblings, 1 reply; 3+ messages in thread
From: Michal Hocko @ 2019-08-13  7:57 UTC (permalink / raw)
  To: Wei Yang; +Cc: akpm, osalvador, linux-mm, linux-kernel

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


^ permalink raw reply	[flat|nested] 3+ messages in thread

* Re: [PATCH] mm/hotplug: prevent memory leak when reuse pgdat
  2019-08-13  7:57 ` Michal Hocko
@ 2019-08-13 13:13   ` Wei Yang
  0 siblings, 0 replies; 3+ messages in thread
From: Wei Yang @ 2019-08-13 13:13 UTC (permalink / raw)
  To: Michal Hocko; +Cc: Wei Yang, akpm, osalvador, linux-mm, linux-kernel

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


^ permalink raw reply	[flat|nested] 3+ messages in thread

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2019-08-13  2:06 [PATCH] mm/hotplug: prevent memory leak when reuse pgdat Wei Yang
2019-08-13  7:57 ` Michal Hocko
2019-08-13 13:13   ` Wei Yang

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