linux-kernel - Re: [PATCH] arch/sparc: support NR

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Date:   Sun, 04 Jun 2017 19:46:53 -0400 (EDT)
From:   David Miller <davem@...emloft.net>
To:     jane.chu@...cle.com
Cc:     tglx@...utronix.de, atish.patra@...cle.com,
        Liam.Howlett@...cle.com, sparclinux@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] arch/sparc: support NR_CPUS = 4096

From: Jane Chu <jane.chu@...cle.com>
Date: Thu,  1 Jun 2017 15:39:13 -0600

> diff --git a/arch/sparc/kernel/irq_64.c b/arch/sparc/kernel/irq_64.c
> index 4d0248a..5b19108 100644
> --- a/arch/sparc/kernel/irq_64.c
> +++ b/arch/sparc/kernel/irq_64.c
> @@ -1034,12 +1034,12 @@ static void __init init_cpu_send_mondo_info(struct trap_per_cpu *tb)
>  {
>  #ifdef CONFIG_SMP
>  	unsigned long page;
> +	unsigned int order;
>  
> -	BUILD_BUG_ON((NR_CPUS * sizeof(u16)) > (PAGE_SIZE - 64));
> -
> -	page = get_zeroed_page(GFP_KERNEL);
> +	order = get_order(num_possible_cpus() * sizeof(u16) + 64);
> +	page = __get_free_pages(GFP_KERNEL | __GFP_ZERO, order);
>  	if (!page) {

The only reason we allocated these two items together was because it
was convenient and it all fit into a single page.

Since it now doesn't, it makes sense to split it up.

Simply use a single page for the cpu_list_pa and kzalloc for the
cpu_mondo_block.

This also allows to keep the BUILD_BUG_ON(), which I really wish
you hadn't tried to remove.

static void __init init_cpu_send_mondo_info(struct trap_per_cpu *tb)
{
#ifdef CONFIG_SMP
	unsigned long page;
	void *mondo;

	BUILD_BUG_ON((NR_CPUS * sizeof(u16)) > PAGE_SIZE);

	mondo = kzalloc(64, GFP_KERNEL);
	if (!mondo) {
		prom_printf("SUN4V: Error, cannot allocate mondo block.\n");
		prom_halt();
	}
	tb->cpu_mondo_block_pa = __pa(mondo);

	page = get_zeroed_page(GFP_KERNEL);
	if (!page) {
		prom_printf("SUN4V: Error, cannot allocate cpu list page.\n");
		prom_halt();
	}
	tb->cpu_list_pa = __pa(page);
#endif
}

Thanks.