linux-kernel - Re: [PATCH v3 04/19] mm: slub: implement SLUB version of obj_to

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Date:   Thu, 21 May 2020 14:06:16 -0700
From:   Roman Gushchin <guro@...com>
To:     Vlastimil Babka <vbabka@...e.cz>
CC:     Andrew Morton <akpm@...ux-foundation.org>,
        Johannes Weiner <hannes@...xchg.org>,
        Michal Hocko <mhocko@...nel.org>, <linux-mm@...ck.org>,
        <kernel-team@...com>, <linux-kernel@...r.kernel.org>,
        Christoph Lameter <cl@...ux.com>
Subject: Re: [PATCH v3 04/19] mm: slub: implement SLUB version of
 obj_to_index()

On Thu, May 21, 2020 at 01:01:38PM +0200, Vlastimil Babka wrote:
> On 5/20/20 11:00 PM, Roman Gushchin wrote:
> > 
> > From beeaecdac85c3a395dcfb99944dc8c858b541cbf Mon Sep 17 00:00:00 2001
> > From: Roman Gushchin <guro@...com>
> > Date: Mon, 29 Jul 2019 18:18:42 -0700
> > Subject: [PATCH v3.2 04/19] mm: slub: implement SLUB version of obj_to_index()
> > 
> > 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>
> 
> Looks good!
> 
> Reviewed-by: Vlastimil Babka <vbabka@...e.cz>

Thanks!