linux-kernel - Re: [PATCH] Fix KMALLOC_MAX_SIZE overflow during cpumask allocation

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Date:	Mon, 8 Dec 2014 11:42:14 +0100
From:	Ingo Molnar <mingo@...nel.org>
To:	Alex Thorlton <athorlton@....com>
Cc:	linux-kernel@...r.kernel.org, George Beshers <gbeshers@....com>,
	Russ Anderson <rja@....com>, Ingo Molnar <mingo@...hat.com>,
	Peter Zijlstra <peterz@...radead.org>
Subject: Re: [PATCH] Fix KMALLOC_MAX_SIZE overflow during cpumask allocation


* Alex Thorlton <athorlton@....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@....com>
> Suggested-by: George Beshers <gbeshers@....com>
> Cc: George Beshers <gbeshers@....com>
> Cc: Russ Anderson <rja@....com>
> Cc: Ingo Molnar <mingo@...hat.com>
> Cc: Peter Zijlstra <peterz@...radead.org>
> Cc: linux-kernel@...r.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
--
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