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Date:   Mon, 16 Sep 2019 15:52:51 +0000
From:   Christopher Lameter <cl@linux.com>
To:     Pengfei Li <lpf.vector@gmail.com>
cc:     akpm@linux-foundation.org, vbabka@suse.cz, penberg@kernel.org,
        rientjes@google.com, iamjoonsoo.kim@lge.com, linux-mm@kvack.org,
        linux-kernel@vger.kernel.org, guro@fb.com
Subject: Re: [PATCH v5 7/7] mm, slab_common: Modify kmalloc_caches[type][idx]
 to kmalloc_caches[idx][type]
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On Mon, 16 Sep 2019, Pengfei Li wrote:

> KMALLOC_NORMAL is the most frequently accessed, and kmalloc_caches[]
> is initialized by different types of the same size.
>
> So modifying kmalloc_caches[type][idx] to kmalloc_caches[idx][type]
> will benefit performance.


Why would that increase performance? Using your scheme means that the
KMALLOC_NORMAL pointers are spread over more cachelines. Since
KMALLOC_NORMAL is most frequently accessed this would cause
a performance regression.