[PATCH] Fix KMALLOC_MAX_SIZE overflow during cpumask allocation

[PATCH] Fix KMALLOC_MAX_SIZE overflow during cpumask allocation

[Alex Thorlton]

When allocating space for load_balance_mask, in sched_init, when
CPUMASK_OFFSTACK is set, we've managed to spill over KMALLOC_MAX_SIZE on our
6144 core machine.  The patch below breaks up the allocations so that they don't
overflow the max alloc size.  It also allocates the masks on the the node from
which they'll most commonly be accessed, to minimize remote accesses on NUMA
machines.

Any input is appreciated!

- Alex

Signed-off-by: Alex Thorlton <athorlton@sgi.com>
Suggested-by: George Beshers <gbeshers@sgi.com>
Cc: George Beshers <gbeshers@sgi.com>
Cc: Russ Anderson <rja@sgi.com>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: linux-kernel@vger.kernel.org

---
 kernel/sched/core.c | 13 ++++---------
 1 file changed, 4 insertions(+), 9 deletions(-)

diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 4499950..8f06655 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -6981,9 +6981,6 @@ void __init sched_init(void)
 #ifdef CONFIG_RT_GROUP_SCHED
 	alloc_size += 2 * nr_cpu_ids * sizeof(void **);
 #endif
-#ifdef CONFIG_CPUMASK_OFFSTACK
-	alloc_size += num_possible_cpus() * cpumask_size();
-#endif
 	if (alloc_size) {
 		ptr = (unsigned long)kzalloc(alloc_size, GFP_NOWAIT);
 
@@ -7003,12 +7000,10 @@ void __init sched_init(void)
 		ptr += nr_cpu_ids * sizeof(void **);
 
 #endif /* CONFIG_RT_GROUP_SCHED */
-#ifdef CONFIG_CPUMASK_OFFSTACK
-		for_each_possible_cpu(i) {
-			per_cpu(load_balance_mask, i) = (void *)ptr;
-			ptr += cpumask_size();
-		}
-#endif /* CONFIG_CPUMASK_OFFSTACK */
+	}
+	for_each_possible_cpu(i) {
+		per_cpu(load_balance_mask, i) = kzalloc_node(
+			cpumask_size(), GFP_KERNEL, cpu_to_node(i));
 	}
 
 	init_rt_bandwidth(&def_rt_bandwidth,
-- 
1.7.12.4

Re: [PATCH] Fix KMALLOC_MAX_SIZE overflow during cpumask allocation

[Ingo Molnar]

* Alex Thorlton <athorlton@sgi.com> wrote:

> When allocating space for load_balance_mask, in sched_init, when
> CPUMASK_OFFSTACK is set, we've managed to spill over KMALLOC_MAX_SIZE on our
> 6144 core machine.  The patch below breaks up the allocations so that they don't
> overflow the max alloc size.  It also allocates the masks on the the node from
> which they'll most commonly be accessed, to minimize remote accesses on NUMA
> machines.
> 
> Any input is appreciated!
> 
> - Alex
> 
> Signed-off-by: Alex Thorlton <athorlton@sgi.com>
> Suggested-by: George Beshers <gbeshers@sgi.com>
> Cc: George Beshers <gbeshers@sgi.com>
> Cc: Russ Anderson <rja@sgi.com>
> Cc: Ingo Molnar <mingo@redhat.com>
> Cc: Peter Zijlstra <peterz@infradead.org>
> Cc: linux-kernel@vger.kernel.org
> 
> ---
>  kernel/sched/core.c | 13 ++++---------
>  1 file changed, 4 insertions(+), 9 deletions(-)
> 
> diff --git a/kernel/sched/core.c b/kernel/sched/core.c
> index 4499950..8f06655 100644
> --- a/kernel/sched/core.c
> +++ b/kernel/sched/core.c
> @@ -6981,9 +6981,6 @@ void __init sched_init(void)
>  #ifdef CONFIG_RT_GROUP_SCHED
>  	alloc_size += 2 * nr_cpu_ids * sizeof(void **);
>  #endif
> -#ifdef CONFIG_CPUMASK_OFFSTACK
> -	alloc_size += num_possible_cpus() * cpumask_size();
> -#endif
>  	if (alloc_size) {
>  		ptr = (unsigned long)kzalloc(alloc_size, GFP_NOWAIT);
>  
> @@ -7003,12 +7000,10 @@ void __init sched_init(void)
>  		ptr += nr_cpu_ids * sizeof(void **);
>  
>  #endif /* CONFIG_RT_GROUP_SCHED */
> -#ifdef CONFIG_CPUMASK_OFFSTACK
> -		for_each_possible_cpu(i) {
> -			per_cpu(load_balance_mask, i) = (void *)ptr;
> -			ptr += cpumask_size();
> -		}
> -#endif /* CONFIG_CPUMASK_OFFSTACK */
> +	}
> +	for_each_possible_cpu(i) {
> +		per_cpu(load_balance_mask, i) = kzalloc_node(
> +			cpumask_size(), GFP_KERNEL, cpu_to_node(i));
>  	}
>  
>  	init_rt_bandwidth(&def_rt_bandwidth,

This patch fails to build with certain configs:

kernel/sched/core.c:7130:33: error: incompatible types when assigning to type ‘cpumask_var_t’ from type ‘void *’

Thanks,

	Ingo

Re: [PATCH] Fix KMALLOC_MAX_SIZE overflow during cpumask allocation

[Alex Thorlton]

On Mon, Dec 08, 2014 at 11:42:14AM +0100, Ingo Molnar wrote:
> This patch fails to build with certain configs:
> 
> kernel/sched/core.c:7130:33: error: incompatible types when assigning to type ‘cpumask_var_t’ from type ‘void *’

Thanks for letting us know, Ingo.  I believe George has something in
mind to fix this.  We'll take a look and get another version out ASAP!

- Alex