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Date:   Tue, 2 Mar 2021 16:42:16 +0100
From:   Michal Hocko <mhocko@suse.com>
To:     Zi Yan <ziy@nvidia.com>
Cc:     "Zhouguanghui (OS Kernel)" <zhouguanghui1@huawei.com>,
        linux-kernel@vger.kernel.org, linux-mm@kvack.org,
        akpm@linux-foundation.org,
        "Wangkefeng (OS Kernel Lab)" <wangkefeng.wang@huawei.com>,
        "Guohanjun (Hanjun Guo)" <guohanjun@huawei.com>,
        Dingtianhong <dingtianhong@huawei.com>,
        Chenweilong <chenweilong@huawei.com>,
        "Xiangrui (Euler)" <rui.xiang@huawei.com>,
        Johannes Weiner <hannes@cmpxchg.org>,
        Vladimir Davydov <vdavydov.dev@gmail.com>,
        Nicholas Piggin <npiggin@gmail.com>
Subject: Re: [PATCH] mm/memcg: set memcg when split pages
Message-ID: <YD5cwFdfocudINWU@dhcp22.suse.cz>
References: <20210302013451.118701-1-zhouguanghui1@huawei.com>
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 <aab0bc059f3b4ffcb7acbac1724bcaa2@huawei.com>
 <1E25514A-202B-48E6-97F2-1E02B0980A96@nvidia.com>
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On Tue 02-03-21 10:37:13, Zi Yan wrote:
[...]
> I have a question on copy_page_memcg above. By reading __memcg_kmem_charge_page
> and __memcg_kmem_uncharge_page, it seems to me that every single page requires
> a css_get(&memcg->css) at charge time and a css_put(&memcg->css) at uncharge time.
> But your copy_page_memcg does not do css_get for split subpages. Will it cause
> memcg->css underflow when subpages are uncharged?

yes, well spotted. I have completely missed that. This will also discard
my comment on testing the memcg.


-- 
Michal Hocko
SUSE Labs