linux-kernel - Re: [PATCH v5 7/7] mm, slab_common: Modify kmalloc_caches[type][idx] to kmalloc

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Message-ID: <0100016d3ac6d132-891c437f-2aeb-41de-84d8-aec48bc20ee4-000000@email.amazonses.com>
Date:   Mon, 16 Sep 2019 15:52:51 +0000
From:   Christopher Lameter <cl@...ux.com>
To:     Pengfei Li <lpf.vector@...il.com>
cc:     akpm@...ux-foundation.org, vbabka@...e.cz, penberg@...nel.org,
        rientjes@...gle.com, iamjoonsoo.kim@....com, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org, guro@...com
Subject: Re: [PATCH v5 7/7] mm, slab_common: Modify kmalloc_caches[type][idx]
 to kmalloc_caches[idx][type]

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.