linux-kernel - Re: [PATCH v2] memcg: refill_stock for kmem uncharging too

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Date:   Thu, 25 Apr 2019 08:48:58 +0200
From:   Michal Hocko <mhocko@...nel.org>
To:     Shakeel Butt <shakeelb@...gle.com>
Cc:     Johannes Weiner <hannes@...xchg.org>,
        Vladimir Davydov <vdavydov.dev@...il.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Roman Gushchin <guro@...com>, linux-mm@...ck.org,
        cgroups@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] memcg: refill_stock for kmem uncharging too

On Tue 23-04-19 08:44:05, Shakeel Butt wrote:
> The commit 475d0487a2ad ("mm: memcontrol: use per-cpu stocks for socket
> memory uncharging") added refill_stock() for skmem uncharging path to
> optimize workloads having high network traffic. Do the same for the kmem
> uncharging as well. Though we can bypass the refill for the offlined
> memcgs but it may impact the performance of network traffic for the
> sockets used by other cgroups.

While the change makes sense, I would really like to see what kind of
effect on performance does it really have. Do you have any specific
workload that benefits from it?

Thanks!

> Signed-off-by: Shakeel Butt <shakeelb@...gle.com>
> Cc: Roman Gushchin <guro@...com>
> Cc: Johannes Weiner <hannes@...xchg.org>
> Cc: Michal Hocko <mhocko@...e.com>
> Cc: Vladimir Davydov <vdavydov.dev@...il.com>
> Cc: Andrew Morton <akpm@...ux-foundation.org>
> ---
> 
> Changelog since v1:
> - No need to bypass offline memcgs in the refill.
> 
>  mm/memcontrol.c | 6 +-----
>  1 file changed, 1 insertion(+), 5 deletions(-)
> 
> diff --git a/mm/memcontrol.c b/mm/memcontrol.c
> index 2535e54e7989..2713b45ec3f0 100644
> --- a/mm/memcontrol.c
> +++ b/mm/memcontrol.c
> @@ -2768,17 +2768,13 @@ void __memcg_kmem_uncharge(struct page *page, int order)
>  	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);
> -
>  	page->mem_cgroup = NULL;
>  
>  	/* slab pages do not have PageKmemcg flag set */
>  	if (PageKmemcg(page))
>  		__ClearPageKmemcg(page);
>  
> -	css_put_many(&memcg->css, nr_pages);
> +	refill_stock(memcg, nr_pages);
>  }
>  #endif /* CONFIG_MEMCG_KMEM */
>  
> -- 
> 2.21.0.593.g511ec345e18-goog
> 

-- 
Michal Hocko
SUSE Labs