linux-kernel - Re: [PATCH v2] mm: memcontrol: Simplify the mem_cgroup_page

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Date:   Thu, 29 Oct 2020 17:13:36 +0100
From:   Michal Hocko <mhocko@...e.com>
To:     Shakeel Butt <shakeelb@...gle.com>
Cc:     Muchun Song <songmuchun@...edance.com>,
        Johannes Weiner <hannes@...xchg.org>,
        Vladimir Davydov <vdavydov.dev@...il.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Roman Gushchin <guro@...com>,
        Joonsoo Kim <iamjoonsoo.kim@....com>,
        Yafang Shao <laoar.shao@...il.com>,
        Chris Down <chris@...isdown.name>,
        Christian Brauner <christian.brauner@...ntu.com>,
        "Peter Zijlstra (Intel)" <peterz@...radead.org>,
        Ingo Molnar <mingo@...nel.org>,
        Kees Cook <keescook@...omium.org>,
        Thomas Gleixner <tglx@...utronix.de>, esyr@...hat.com,
        Suren Baghdasaryan <surenb@...gle.com>, areber@...hat.com,
        Marco Elver <elver@...gle.com>,
        LKML <linux-kernel@...r.kernel.org>,
        Cgroups <cgroups@...r.kernel.org>, Linux MM <linux-mm@...ck.org>
Subject: Re: [PATCH v2] mm: memcontrol: Simplify the mem_cgroup_page_lruvec

On Thu 29-10-20 09:01:37, Shakeel Butt wrote:
> On Thu, Oct 29, 2020 at 2:08 AM Michal Hocko <mhocko@...e.com> wrote:
> >
> > On Wed 28-10-20 11:50:13, Muchun Song wrote:
> > [...]
> > > -struct lruvec *mem_cgroup_page_lruvec(struct page *page, struct pglist_data *pgdat)
> > > +static struct lruvec *
> > > +__mem_cgroup_node_lruvec(struct mem_cgroup *memcg, struct pglist_data *pgdat,
> > > +                      int nid)
> >
> > I thought I have made it clear that this is not a good approach. Please
> > do not repost new version without that being addressed. If there are any
> > questions then feel free to ask for details.
> 
> You can get nid from pgdat (pgdat->node_id) and also pgdat from nid
> (NODE_DATA(nid)), so, __mem_cgroup_node_lruvec() only need one of them
> as parameter.

Exactly what I've said in the previous version review. I suspect that
the issue is that mem_cgroup_page_nodeinfo (based on page's node_id)
and the given pgdat can mismatch in the existing code but that shouldn't
be a real problem because the mismatch can only happen for lruvec->pgdat
== NULL unless I am missing something.

-- 
Michal Hocko
SUSE Labs