linux-kernel - Re: [PATCH v6 04/19] mm: slub: implement SLUB version of obj_to

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Date:   Tue, 16 Jun 2020 20:08:35 -0700
From:   Shakeel Butt <shakeelb@...gle.com>
To:     Roman Gushchin <guro@...com>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Christoph Lameter <cl@...ux.com>,
        Johannes Weiner <hannes@...xchg.org>,
        Michal Hocko <mhocko@...nel.org>,
        Linux MM <linux-mm@...ck.org>,
        Vlastimil Babka <vbabka@...e.cz>,
        Kernel Team <kernel-team@...com>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v6 04/19] mm: slub: implement SLUB version of obj_to_index()

On Mon, Jun 8, 2020 at 4:07 PM Roman Gushchin <guro@...com> wrote:
>
> This commit implements SLUB version of the obj_to_index() function,
> which will be required to calculate the offset of obj_cgroup in the
> obj_cgroups vector to store/obtain the objcg ownership data.
>
> To make it faster, let's repeat the SLAB's trick introduced by
> commit 6a2d7a955d8d ("[PATCH] SLAB: use a multiply instead of a
> divide in obj_to_index()") and avoid an expensive division.
>
> Vlastimil Babka noticed, that SLUB does have already a similar
> function called slab_index(), which is defined only if SLUB_DEBUG
> is enabled. The function does a similar math, but with a division,
> and it also takes a page address instead of a page pointer.
>
> Let's remove slab_index() and replace it with the new helper
> __obj_to_index(), which takes a page address. obj_to_index()
> will be a simple wrapper taking a page pointer and passing
> page_address(page) into __obj_to_index().
>
> Signed-off-by: Roman Gushchin <guro@...com>
> Reviewed-by: Vlastimil Babka <vbabka@...e.cz>
> Acked-by: Johannes Weiner <hannes@...xchg.org>

Reviewed-by: Shakeel Butt <shakeelb@...gle.com>