linux-kernel - Re: [PATCH] mm, slub: Use prefetchw instead of prefetch

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Message-ID: <alpine.DEB.2.22.394.2110110919050.130815@gentwo.de>
Date:   Mon, 11 Oct 2021 09:20:36 +0200 (CEST)
From:   Christoph Lameter <cl@...two.de>
To:     Hyeonggon Yoo <42.hyeyoo@...il.com>
cc:     linux-mm@...ck.org, linux-kernel@...r.kernel.org,
        Pekka Enberg <penberg@...nel.org>,
        David Rientjes <rientjes@...gle.com>,
        Joonsoo Kim <iamjoonsoo.kim@....com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Vlastimil Babka <vbabka@...e.cz>
Subject: Re: [PATCH] mm, slub: Use prefetchw instead of prefetch

On Fri, 8 Oct 2021, Hyeonggon Yoo wrote:

> It's certain that an object will be not only read, but also
> written after allocation.

get_freepointer is used in multiple code path not only in allocation. It
is for example used when scanning through a freelist.

With this change all objects get needlessly dirtied and the cross cpu
cache contention is increased.