Re: [PATCH 4/4] kstat: modify kstat_irqs_legacy to be variable sized

Ingo Molnar
2009-01-10T22:53:14Z

* Mike Travis <travis@sgi.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@sgi.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