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

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Message-ID: <849c3d62-8bb1-e1f4-3fc4-68fa71484a2b@oracle.com>
Date:   Mon, 5 Jun 2017 12:15:41 -0700
From:   jane.chu@...cle.com
To:     David Miller <davem@...emloft.net>
Cc:     tglx@...utronix.de, atish.patra@...cle.com,
        Liam.Howlett@...cle.com, sparclinux@...r.kernel.org,
        linux-kernel@...r.kernel.org, "JANE.CHU" <jane.chu@...cle.com>
Subject: Re: [PATCH] arch/sparc: support NR_CPUS = 4096

Hi, David,


On 06/04/2017 04:46 PM, David Miller wrote:
> 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.

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.