linux-kernel - Re: [PATCH v4 2/4] mm: memcg: add a helper for non-unified stats flushing

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Message-ID: <ZPXtejIUIKg/IyZ6@dhcp22.suse.cz>
Date:   Mon, 4 Sep 2023 16:45:14 +0200
From:   Michal Hocko <mhocko@...e.com>
To:     Yosry Ahmed <yosryahmed@...gle.com>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Johannes Weiner <hannes@...xchg.org>,
        Roman Gushchin <roman.gushchin@...ux.dev>,
        Shakeel Butt <shakeelb@...gle.com>,
        Muchun Song <muchun.song@...ux.dev>,
        Ivan Babrou <ivan@...udflare.com>, Tejun Heo <tj@...nel.org>,
        Michal Koutný <mkoutny@...e.com>,
        Waiman Long <longman@...hat.com>, linux-mm@...ck.org,
        cgroups@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v4 2/4] mm: memcg: add a helper for non-unified stats
 flushing

On Thu 31-08-23 16:56:09, Yosry Ahmed wrote:
> Some contexts flush memcg stats outside of unified flushing, directly
> using cgroup_rstat_flush(). Add a helper for non-unified flushing, a
> counterpart for do_unified_stats_flush(), and use it in those contexts,
> as well as in do_unified_stats_flush() itself.
> 
> This abstracts the rstat API and makes it easy to introduce
> modifications to either unified or non-unified flushing functions
> without changing callers.
> 
> No functional change intended.
> 
> Signed-off-by: Yosry Ahmed <yosryahmed@...gle.com>

Acked-by: Michal Hocko <mhocko@...e.com>

> ---
>  mm/memcontrol.c | 21 +++++++++++++++++----
>  1 file changed, 17 insertions(+), 4 deletions(-)
> 
> diff --git a/mm/memcontrol.c b/mm/memcontrol.c
> index 2d0ec828a1c4..8c046feeaae7 100644
> --- a/mm/memcontrol.c
> +++ b/mm/memcontrol.c
> @@ -639,6 +639,17 @@ static inline void memcg_rstat_updated(struct mem_cgroup *memcg, int val)
>  	}
>  }
>  
> +/*
> + * do_stats_flush - do a flush of the memory cgroup statistics
> + * @memcg: memory cgroup to flush
> + *
> + * Only flushes the subtree of @memcg, does not skip under any conditions.
> + */
> +static void do_stats_flush(struct mem_cgroup *memcg)
> +{
> +	cgroup_rstat_flush(memcg->css.cgroup);
> +}
> +
>  /*
>   * do_unified_stats_flush - do a unified flush of memory cgroup statistics
>   *
> @@ -656,7 +667,7 @@ static void do_unified_stats_flush(void)
>  
>  	WRITE_ONCE(flush_next_time, jiffies_64 + 2*FLUSH_TIME);
>  
> -	cgroup_rstat_flush(root_mem_cgroup->css.cgroup);
> +	do_stats_flush(root_mem_cgroup);
>  
>  	atomic_set(&stats_flush_threshold, 0);
>  	atomic_set(&stats_unified_flush_ongoing, 0);
> @@ -7790,7 +7801,7 @@ bool obj_cgroup_may_zswap(struct obj_cgroup *objcg)
>  			break;
>  		}
>  
> -		cgroup_rstat_flush(memcg->css.cgroup);
> +		do_stats_flush(memcg);
>  		pages = memcg_page_state(memcg, MEMCG_ZSWAP_B) / PAGE_SIZE;
>  		if (pages < max)
>  			continue;
> @@ -7855,8 +7866,10 @@ void obj_cgroup_uncharge_zswap(struct obj_cgroup *objcg, size_t size)
>  static u64 zswap_current_read(struct cgroup_subsys_state *css,
>  			      struct cftype *cft)
>  {
> -	cgroup_rstat_flush(css->cgroup);
> -	return memcg_page_state(mem_cgroup_from_css(css), MEMCG_ZSWAP_B);
> +	struct mem_cgroup *memcg = mem_cgroup_from_css(css);
> +
> +	do_stats_flush(memcg);
> +	return memcg_page_state(memcg, MEMCG_ZSWAP_B);
>  }
>  
>  static int zswap_max_show(struct seq_file *m, void *v)
> -- 
> 2.42.0.rc2.253.gd59a3bf2b4-goog

-- 
Michal Hocko
SUSE Labs