linux-kernel - Re: [PATCH] mm/memcontrol:rewrite mem_cgroup_page

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Message-Id: <20201106173014.e13b5fe5edec41d1f7fdf072@linux-foundation.org>
Date:   Fri, 6 Nov 2020 17:30:14 -0800
From:   Andrew Morton <akpm@...ux-foundation.org>
To:     Hui Su <sh_def@....com>
Cc:     hannes@...xchg.org, mhocko@...nel.org, vdavydov.dev@...il.com,
        shakeelb@...gle.com, guro@...com, laoar.shao@...il.com,
        chris@...isdown.name, linux-kernel@...r.kernel.org,
        cgroups@...r.kernel.org, linux-mm@...ck.org
Subject: Re: [PATCH] mm/memcontrol:rewrite mem_cgroup_page_lruvec()

On Wed, 4 Nov 2020 22:25:16 +0800 Hui Su <sh_def@....com> wrote:

> mem_cgroup_page_lruvec() in memcontrol.c and
> mem_cgroup_lruvec() in memcontrol.h is very similar
> except for the param(page and memcg) which also can be
> convert to each other.
> 
> So rewrite mem_cgroup_page_lruvec() with mem_cgroup_lruvec().

Alex Shi's "mm/memcg: warning on !memcg after readahead page charged"
(https://lkml.kernel.org/r/1604283436-18880-3-git-send-email-alex.shi@linux.alibaba.com)
changes mem_cgroup_page_lruvec() thusly:

--- a/mm/memcontrol.c~mm-memcg-warning-on-memcg-after-readahead-page-charged
+++ a/mm/memcontrol.c
@@ -1325,10 +1325,7 @@ struct lruvec *mem_cgroup_page_lruvec(st
 	}
 
 	memcg = page_memcg(page);
-	/*
-	 * Swapcache readahead pages are added to the LRU - and
-	 * possibly migrated - before they are charged.
-	 */
+	VM_WARN_ON_ONCE_PAGE(!memcg, page);
 	if (!memcg)
 		memcg = root_mem_cgroup;
 
So the patch didn't apply.

That's easily fixed, but it does make one wonder whether this:

> -struct lruvec *mem_cgroup_page_lruvec(struct page *, struct pglist_data *);
> +/**
> + * mem_cgroup_page_lruvec - return lruvec for isolating/putting an LRU page
> + * @page: the page
> + * @pgdat: pgdat of the page
> + *
> + * This function relies on page->mem_cgroup being stable.
> + */
> +static inline struct lruvec *mem_cgroup_page_lruvec(struct page *page,
> +						struct pglist_data *pgdat)
> +{
> +	struct mem_cgroup *memcg = page->mem_cgroup;
> +
> +	return mem_cgroup_lruvec(memcg, pgdat);
> +}

Should be using page_memcg()?