linux-kernel - Re: [PATCH v2 2/2] mm/memcg: set memcg when split page

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Message-ID: <YEECKZBBWpK/Gl6R@cmpxchg.org>
Date:   Thu, 4 Mar 2021 10:52:09 -0500
From:   Johannes Weiner <hannes@...xchg.org>
To:     Zhou Guanghui <zhouguanghui1@...wei.com>
Cc:     linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        akpm@...ux-foundation.org, mhocko@...e.com, hughd@...gle.com,
        kirill.shutemov@...ux.intel.com, npiggin@...il.com, ziy@...dia.com,
        wangkefeng.wang@...wei.com, guohanjun@...wei.com,
        dingtianhong@...wei.com, chenweilong@...wei.com,
        rui.xiang@...wei.com
Subject: Re: [PATCH v2 2/2] mm/memcg: set memcg when split page

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@...wei.com>

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