linux-kernel - Re: [PATCH v2] arch/sparc: support NR

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Date:   Tue, 6 Jun 2017 10:04:25 -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
Subject: Re: [PATCH v2] arch/sparc: support NR_CPUS = 4096

On 06/05/2017 08:27 PM, David Miller wrote:

> From: jane.chu@...cle.com
> Date: Mon, 5 Jun 2017 20:03:28 -0700
>
>> On sun4v sparc, it looks like kzalloc(64, GFP_KERNEL) ends up
>> allocating from kmalloc_caches[6] - a 64-byte kmem-cache allocated
>> by kmem_cache_init() with SLAB_HWCACHE_ALIGN flag set, so it's in
>> l3-cache-line-size alignment, i.e. 64byte.  I printed out the
>> 'mondo' pa and verified that.
> Please check this, because that is an implementation detail.  We have
> three SLAB allocators.
>
> For example, if the user enables SLOB, I bet you don't get that
> alignment.
>
> The only thing we are universally guaranteed is ARCH_KMALLOC_MINALIGN.
>
> Please implement this properly, rather than relying upon things like
> the above.

Good point, agreed.  I will update the patch.

thanks!
-jane

>
> Thank you.