linux-kernel - Re: [PATCH] mm: memcg/slab: optimize objcg stock draining

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Message-Id: <20210106115044.c4393afa1ad61ef3f8db1d94@linux-foundation.org>
Date:   Wed, 6 Jan 2021 11:50:44 -0800
From:   Andrew Morton <akpm@...ux-foundation.org>
To:     Roman Gushchin <guro@...com>
Cc:     <linux-mm@...ck.org>, Michal Hocko <mhocko@...nel.org>,
        Johannes Weiner <hannes@...xchg.org>,
        Shakeel Butt <shakeelb@...gle.com>,
        <linux-kernel@...r.kernel.org>, <kernel-team@...com>,
        Imran Khan <imran.f.khan@...cle.com>
Subject: Re: [PATCH] mm: memcg/slab: optimize objcg stock draining

On Tue, 5 Jan 2021 20:22:39 -0800 Roman Gushchin <guro@...com> wrote:

> Imran Khan reported a regression in hackbench results caused by the
> commit f2fe7b09a52b ("mm: memcg/slab: charge individual slab objects
> instead of pages").

How large was the regression?

> --- a/mm/memcontrol.c
> +++ b/mm/memcontrol.c
> @@ -3122,9 +3122,7 @@ void __memcg_kmem_uncharge(struct mem_cgroup *memcg, unsigned int nr_pages)
>  	if (!cgroup_subsys_on_dfl(memory_cgrp_subsys))
>  		page_counter_uncharge(&memcg->kmem, nr_pages);
>  
> -	page_counter_uncharge(&memcg->memory, nr_pages);
> -	if (do_memsw_account())
> -		page_counter_uncharge(&memcg->memsw, nr_pages);
> +	refill_stock(memcg, nr_pages);
>  }

IOW, which kernel version(s) should we be patching?