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

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Message-ID: <20200504182922.GA20009@carbon.dhcp.thefacebook.com>
Date:   Mon, 4 May 2020 11:29:22 -0700
From:   Roman Gushchin <guro@...com>
To:     Christopher Lameter <cl@...ux.com>
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>
Subject: Re: [PATCH v3 04/19] mm: slub: implement SLUB version of
 obj_to_index()

On Sat, May 02, 2020 at 11:54:09PM +0000, Christoph Lameter wrote:
> On Thu, 30 Apr 2020, Roman Gushchin wrote:
> 
> > Sorry, but what exactly do you mean?
> 
> I think the right approach is to add a pointer to each slab object for
> memcg support.
>

As I understand, embedding the memcg pointer will hopefully make allocations
cheaper in terms of CPU, but will require more memory. And you think that
it's worth it. Is it a correct understanding?

Can you, please, describe a bit more detailed how it should be done
from your point of view?
I mean where to store the pointer, should it be SLAB/SLUB-specific code
or a generic code, what do to with kmallocs alignments, should we
merge slabs which had a different size before and now have the same
because of the memcg pointer and aligment, etc.

I'm happy to follow your advice and perform some tests to get an idea of
how significant the memory overhead is and how big are CPU savings.
I guess with these numbers it will be easy to make a decision.

Thanks!