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Date:   Thu, 4 Mar 2021 10:52:09 -0500
From:   Johannes Weiner <hannes@cmpxchg.org>
To:     Zhou Guanghui <zhouguanghui1@huawei.com>
Cc:     linux-kernel@vger.kernel.org, linux-mm@kvack.org,
        akpm@linux-foundation.org, mhocko@suse.com, hughd@google.com,
        kirill.shutemov@linux.intel.com, npiggin@gmail.com, ziy@nvidia.com,
        wangkefeng.wang@huawei.com, guohanjun@huawei.com,
        dingtianhong@huawei.com, chenweilong@huawei.com,
        rui.xiang@huawei.com
Subject: Re: [PATCH v2 2/2] mm/memcg: set memcg when split page
Message-ID: <YEECKZBBWpK/Gl6R@cmpxchg.org>
References: <20210304074053.65527-1-zhouguanghui1@huawei.com>
 <20210304074053.65527-3-zhouguanghui1@huawei.com>
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On Thu, Mar 04, 2021 at 07:40:53AM +0000, Zhou Guanghui wrote:
> As described in the split_page function comment, for the non-compound
> high order page, the sub-pages must be freed individually. If the
> memcg of the fisrt page is valid, the tail pages cannot be uncharged
> when be freed.
> 
> For example, when alloc_pages_exact is used to allocate 1MB continuous
> physical memory, 2MB is charged(kmemcg is enabled and __GFP_ACCOUNT is
> set). When make_alloc_exact free the unused 1MB and free_pages_exact
> free the applied 1MB, actually, only 4KB(one page) is uncharged.
> 
> Therefore, the memcg of the tail page needs to be set when split page.
> 
> Signed-off-by: Zhou Guanghui <zhouguanghui1@huawei.com>

Acked-by: Johannes Weiner <hannes@cmpxchg.org>