linux-kernel - Re: [PATCH v2] writeback: use exact memcg dirty counts

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Date:   Mon, 1 Apr 2019 14:20:44 -0400
From:   Johannes Weiner <hannes@...xchg.org>
To:     Greg Thelen <gthelen@...gle.com>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Roman Gushchin <guro@...com>, Michal Hocko <mhocko@...nel.org>,
        Vladimir Davydov <vdavydov.dev@...il.com>,
        Tejun Heo <tj@...nel.org>, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org, stable@...r.kernel.org
Subject: Re: [PATCH v2] writeback: use exact memcg dirty counts

On Fri, Mar 29, 2019 at 10:46:09AM -0700, Greg Thelen wrote:
> @@ -3907,10 +3923,10 @@ void mem_cgroup_wb_stats(struct bdi_writeback *wb, unsigned long *pfilepages,
>  	struct mem_cgroup *memcg = mem_cgroup_from_css(wb->memcg_css);
>  	struct mem_cgroup *parent;
>  
> -	*pdirty = memcg_page_state(memcg, NR_FILE_DIRTY);
> +	*pdirty = memcg_exact_page_state(memcg, NR_FILE_DIRTY);
>  
>  	/* this should eventually include NR_UNSTABLE_NFS */
> -	*pwriteback = memcg_page_state(memcg, NR_WRITEBACK);
> +	*pwriteback = memcg_exact_page_state(memcg, NR_WRITEBACK);
>  	*pfilepages = mem_cgroup_nr_lru_pages(memcg, (1 << LRU_INACTIVE_FILE) |
>  						     (1 << LRU_ACTIVE_FILE));

Andrew,

just a head-up: -mm has that LRU stat cleanup series queued ("mm:
memcontrol: clean up the LRU counts tracking") that changes the
mem_cgroup_nr_lru_pages() call here to two memcg_page_state().

I'm assuming Greg's fix here will get merged before the cleanup. When
it gets picked up, it'll conflict with "mm: memcontrol: push down
mem_cgroup_nr_lru_pages()".

"mm: memcontrol: push down mem_cgroup_nr_lru_pages()" will need to be
changed to use memcg_exact_page_state() calls instead of the plain
memcg_page_state() for *pfilepages.

Thanks