Re: [PATCH] arch/sparc: support NR_CPUS = 4096

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Hi, David,


On 06/04/2017 04:46 PM, David Miller wrote:
From: Jane Chu <jane.chu@xxxxxxxxxx>
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.

Good point!  I will just add a comment for future maintenance that
the mondo trap block needs to be 64byte aligned.

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 a lot!

-jane


Thanks.

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