linux-kernel - Re: [PATCH 4/4] kstat: modify kstat_irqs

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Date:	Sat, 10 Jan 2009 23:52:29 +0100
From:	Ingo Molnar <mingo@...e.hu>
To:	Mike Travis <travis@....com>,
	Andrew Morton <akpm@...ux-foundation.org>
Cc:	Ingo Molnar <mingo@...hat.com>,
	Rusty Russell <rusty@...tcorp.com.au>,
	Yinghai Lu <yinghai@...nel.org>,
	Jack Steiner <steiner@....com>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 4/4] kstat: modify kstat_irqs_legacy to be variable
	sized


* Mike Travis <travis@....com> wrote:

> Impact: reduce memory usage.
> 
> Allocate kstat_irqs_legacy based on nr_cpu_ids to deal with this
> memory usage bump when NR_CPUS bumped from 128 to 4096:
> 
>      8192   +253952    262144 +3100%  kstat_irqs_legacy(.bss)
> 
> This is only when CONFIG_SPARSE_IRQS=y.
> 
> Signed-off-by: Mike Travis <travis@....com>
> ---
>  kernel/irq/handle.c |    9 ++++++---
>  1 file changed, 6 insertions(+), 3 deletions(-)
> 
> --- linux-2.6-for-ingo.orig/kernel/irq/handle.c
> +++ linux-2.6-for-ingo/kernel/irq/handle.c
> @@ -124,8 +124,7 @@ static struct irq_desc irq_desc_legacy[N
>  	}
>  };
>  
> -/* FIXME: use bootmem alloc ...*/
> -static unsigned int kstat_irqs_legacy[NR_IRQS_LEGACY][NR_CPUS];
> +static unsigned int *kstat_irqs_legacy;
>  
>  int __init early_irq_init(void)
>  {
> @@ -146,9 +145,13 @@ int __init early_irq_init(void)
>  	/* allocate irq_desc_ptrs array based on nr_irqs */
>  	irq_desc_ptrs = alloc_bootmem(nr_irqs * sizeof(void *));
>  
> +	/* allocate based on nr_cpu_ids */
> +	kstat_irqs_legacy = alloc_bootmem(NR_IRQS_LEGACY * nr_cpu_ids *
> +					  sizeof(int));
> +
>  	for (i = 0; i < legacy_count; i++) {
>  		desc[i].irq = i;
> -		desc[i].kstat_irqs = kstat_irqs_legacy[i];
> +		desc[i].kstat_irqs = kstat_irqs_legacy + i * NR_IRQS_LEGACY;
>  		lockdep_set_class(&desc[i].lock, &irq_desc_lock_class);
>  		init_alloc_desc_masks(&desc[i], 0, true);
>  		irq_desc_ptrs[i] = desc + i;

btw., while at it - dont we want to upgrade this to a 'long' (in a 
separate commit)? Having more than 4 billion irqs after bootup is easily 
possible.

	Ingo
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