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Date:   Thu, 15 Apr 2021 12:40:10 -0400
From:   Johannes Weiner <hannes@cmpxchg.org>
To:     Waiman Long <longman@redhat.com>
Cc:     Michal Hocko <mhocko@kernel.org>,
        Vladimir Davydov <vdavydov.dev@gmail.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        Tejun Heo <tj@kernel.org>, Christoph Lameter <cl@linux.com>,
        Pekka Enberg <penberg@kernel.org>,
        David Rientjes <rientjes@google.com>,
        Joonsoo Kim <iamjoonsoo.kim@lge.com>,
        Vlastimil Babka <vbabka@suse.cz>, Roman Gushchin <guro@fb.com>,
        linux-kernel@vger.kernel.org, cgroups@vger.kernel.org,
        linux-mm@kvack.org, Shakeel Butt <shakeelb@google.com>,
        Muchun Song <songmuchun@bytedance.com>,
        Alex Shi <alex.shi@linux.alibaba.com>,
        Chris Down <chris@chrisdown.name>,
        Yafang Shao <laoar.shao@gmail.com>,
        Wei Yang <richard.weiyang@gmail.com>,
        Masayoshi Mizuma <msys.mizuma@gmail.com>,
        Xing Zhengjun <zhengjun.xing@linux.intel.com>
Subject: Re: [PATCH v3 1/5] mm/memcg: Pass both memcg and lruvec to
 mod_memcg_lruvec_state()
Message-ID: <YHhsapGx3vTlyZvF@cmpxchg.org>
References: <20210414012027.5352-1-longman@redhat.com>
 <20210414012027.5352-2-longman@redhat.com>
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On Tue, Apr 13, 2021 at 09:20:23PM -0400, Waiman Long wrote:
> The caller of mod_memcg_lruvec_state() has both memcg and lruvec readily
> available. So both of them are now passed to mod_memcg_lruvec_state()
> and __mod_memcg_lruvec_state(). The __mod_memcg_lruvec_state() is
> updated to allow either of the two parameters to be set to null. This
> makes mod_memcg_lruvec_state() equivalent to mod_memcg_state() if lruvec
> is null.
> 
> The new __mod_memcg_lruvec_state() function will be used in the next
> patch as a replacement of mod_memcg_state() in mm/percpu.c for the
> consolidation of the memory uncharge and vmstat update functions in
> the kmem_cache_free() path.

This requires users who want both to pass a pgdat that can be derived
from the lruvec. This is error prone, and we just acked a patch that
removes this very thing from mem_cgroup_page_lruvec().

With the suggestion for patch 2, this shouldn't be necessary anymore,
though. And sort of underlines my point around that combined function
creating akwward code above and below it.