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

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Date:   Mon, 05 Jun 2017 23:27:24 -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 v2] arch/sparc: support NR_CPUS = 4096

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.

Thank you.