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Subject: Re: [PATCH 05/18] mm: memcontrol: convert page cache to a new
 mem_cgroup_charge() API
To:     Johannes Weiner <hannes@cmpxchg.org>,
        Joonsoo Kim <js1304@gmail.com>
Cc:     Shakeel Butt <shakeelb@google.com>,
        Hugh Dickins <hughd@google.com>,
        Michal Hocko <mhocko@suse.com>,
        "Kirill A. Shutemov" <kirill@shutemov.name>,
        Roman Gushchin <guro@fb.com>, linux-mm@kvack.org,
        cgroups@vger.kernel.org, linux-kernel@vger.kernel.org,
        kernel-team@fb.com
References: <20200420221126.341272-1-hannes@cmpxchg.org>
 <20200420221126.341272-6-hannes@cmpxchg.org>
From:   Alex Shi <alex.shi@linux.alibaba.com>
Message-ID: <e3d70030-a9ae-a679-9cf9-1cd5b680650e@linux.alibaba.com>
Date:   Tue, 21 Apr 2020 17:12:11 +0800
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?? 2020/4/21 ????6:11, Johannes Weiner д??:
> The try/commit/cancel protocol that memcg uses dates back to when
> pages used to be uncharged upon removal from the page cache, and thus
> couldn't be committed before the insertion had succeeded. Nowadays,
> pages are uncharged when they are physically freed; it doesn't matter
> whether the insertion was successful or not. For the page cache, the
> transaction dance has become unnecessary.
> 
> Introduce a mem_cgroup_charge() function that simply charges a newly
> allocated page to a cgroup and sets up page->mem_cgroup in one single
> step. If the insertion fails, the caller doesn't have to do anything
> but free/put the page.
> 
> Then switch the page cache over to this new API.
> 
> Subsequent patches will also convert anon pages, but it needs a bit
> more prep work. Right now, memcg depends on page->mapping being
> already set up at the time of charging, so that it can maintain its
> own MEMCG_CACHE and MEMCG_RSS counters. For anon, page->mapping is set
> under the same pte lock under which the page is publishd, so a single
> charge point that can block doesn't work there just yet.
> 
> The following prep patches will replace the private memcg counters
> with the generic vmstat counters, thus removing the page->mapping
> dependency, then complete the transition to the new single-point
> charge API and delete the old transactional scheme.
> 
> Signed-off-by: Johannes Weiner <hannes@cmpxchg.org>
> ---

Reviewed-by: Alex Shi <alex.shi@linux.alibaba.com>