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Subject: Re: [PATCH 03/18] mm: memcontrol: drop @compound parameter from memcg
 charging 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>
 <20200420221126.341272-4-hannes@cmpxchg.org>
From:   Alex Shi <alex.shi@linux.alibaba.com>
Message-ID: <73c1a95f-fee9-716d-c72f-85585de13f2f@linux.alibaba.com>
Date:   Tue, 21 Apr 2020 17:11:08 +0800
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?? 2020/4/21 ????6:11, Johannes Weiner д??:
> The memcg charging API carries a boolean @compound parameter that
> tells whether the page we're dealing with is a hugepage.
> mem_cgroup_commit_charge() has another boolean @lrucare that indicates
> whether the page needs LRU locking or not while charging. The majority
> of callsites know those parameters at compile time, which results in a
> lot of naked "false, false" argument lists. This makes for cryptic
> code and is a breeding ground for subtle mistakes.
> 
> Thankfully, the huge page state can be inferred from the page itself
> and doesn't need to be passed along. This is safe because charging
> completes before the page is published and somebody may split it.
> 
> Simplify the callsites by removing @compound, and let memcg infer the
> state by using hpage_nr_pages() unconditionally. That function does
> PageTransHuge() to identify huge pages, which also helpfully asserts
> that nobody passes in tail pages by accident.
> 
> The following patches will introduce a new charging API, best not to
> carry over unnecessary weight.
> 
> Signed-off-by: Johannes Weiner <hannes@cmpxchg.org>

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