linux-kernel - Re: [RFC PATCH] cgroup: introduce proportional protection on memcg

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Message-ID: <CAGWkznGAmML4XB0t5jOZEoafQrFk=gXvP96Lmgh221Y22bUuyw@mail.gmail.com>
Date:   Fri, 25 Mar 2022 11:08:00 +0800
From:   Zhaoyang Huang <huangzhaoyang@...il.com>
To:     Chris Down <chris@...isdown.name>
Cc:     "zhaoyang.huang" <zhaoyang.huang@...soc.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Johannes Weiner <hannes@...xchg.org>,
        Michal Hocko <mhocko@...nel.org>,
        Vladimir Davydov <vdavydov.dev@...il.com>,
        ke wang <ke.wang@...soc.com>,
        "open list:MEMORY MANAGEMENT" <linux-mm@...ck.org>,
        LKML <linux-kernel@...r.kernel.org>, cgroups@...r.kernel.org
Subject: Re: [RFC PATCH] cgroup: introduce proportional protection on memcg

On Fri, Mar 25, 2022 at 11:02 AM Zhaoyang Huang <huangzhaoyang@...il.com> wrote:
>
> On Thu, Mar 24, 2022 at 10:27 PM Chris Down <chris@...isdown.name> wrote:
> >
> > I'm confused by the aims of this patch. We already have proportional reclaim
> > for memory.min and memory.low, and memory.high is already "proportional" by its
> > nature to drive memory back down behind the configured threshold.
> >
> > Could you please be more clear about what you're trying to achieve and in what
> > way the existing proportional reclaim mechanisms are insufficient for you?

sorry for the bad formatting of previous reply, resend it in new format

 What I am trying to solve is that, the memcg's protection judgment[1]
 is based on a set of fixed value on current design, while the real
 scan and reclaim number[2] is based on the proportional min/low on the
 real memory usage which you mentioned above. Fixed value setting has
 some constraints as
 1. It is an experienced value based on observation, which could be inaccurate.
 2. working load is various from scenarios.
 3. fixed value from [1] could be against the dynamic cgroup_size in [2].

 shrink_node_memcgs
[1] check if the memcg is protected based on fixed min/low value
     mem_cgroup_calculate_protection(target_memcg, memcg);
      if (mem_cgroup_below_min(memcg))
      ...
      else if (mem_cgroup_below_low(memcg))
      ...

[2] calculate the number of scan size proportionally
     shrink_lruvec
             get_scan_count
                    mem_cgroup_protection
                    scan = lruvec_size - lruvec_size * protection /
(cgroup_size + 1);