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Date:   Thu, 10 Dec 2020 17:00:45 +0100
From:   Johannes Weiner <hannes@cmpxchg.org>
To:     Muchun Song <songmuchun@bytedance.com>
Cc:     gregkh@linuxfoundation.org, rafael@kernel.org, adobriyan@gmail.com,
        akpm@linux-foundation.org, mhocko@kernel.org,
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Subject: Re: [RESEND PATCH v2 01/12] mm: memcontrol: fix NR_ANON_THPS account
Message-ID: <20201210160045.GF264602@cmpxchg.org>
References: <20201206101451.14706-1-songmuchun@bytedance.com>
 <20201206101451.14706-2-songmuchun@bytedance.com>
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On Sun, Dec 06, 2020 at 06:14:40PM +0800, Muchun Song wrote:
> The unit of NR_ANON_THPS is HPAGE_PMD_NR already. So it should inc/dec
> by one rather than nr_pages.

This is a real bug, thanks for catching it.

However, your patch changes the user-visible output of /proc/vmstat!

NR_ANON_THPS isn't just used by memcg, it's a generic accounting item
of the memory subsystem. See this from the Fixes:-patch:

-                       __inc_node_page_state(page, NR_ANON_THPS);
+                       __inc_lruvec_page_state(page, NR_ANON_THPS);

While we've considered /proc/vmstat less official than other files
like meminfo, and have in the past freely added and removed items,
changing the unit of an existing one is not going to work.