From: Vladimir Davydov <vdavydov.dev@gmail.com>
To: Sean Christopherson <sean.j.christopherson@intel.com>
Cc: mhocko@kernel.org, hannes@cmpxchg.org, cgroups@vger.kernel.org,
linux-mm@kvack.org
Subject: Re: [PATCH] mm/memcontrol: exclude @root from checks in mem_cgroup_low
Date: Sat, 3 Jun 2017 22:15:53 +0300 [thread overview]
Message-ID: <20170603191553.GG15130@esperanza> (raw)
In-Reply-To: <1496434412-21005-1-git-send-email-sean.j.christopherson@intel.com>
On Fri, Jun 02, 2017 at 01:13:32PM -0700, Sean Christopherson wrote:
> Make @root exclusive in mem_cgroup_low; it is never considered low
> when looked at directly and is not checked when traversing the tree.
> In effect, @root is handled identically to how root_mem_cgroup was
> previously handled by mem_cgroup_low.
>
> If @root is not excluded from the checks, a cgroup underneath @root
> will never be considered low during targeted reclaim of @root, e.g.
> due to memory.current > memory.high, unless @root is misconfigured
> to have memory.low > memory.high.
>
> Excluding @root enables using memory.low to prioritize memory usage
> between cgroups within a subtree of the hierarchy that is limited by
> memory.high or memory.max, e.g. when ROOT owns @root's controls but
> delegates the @root directory to a USER so that USER can create and
> administer children of @root.
>
> For example, given cgroup A with children B and C:
>
> A
> / \
> B C
>
> and
>
> 1. A/memory.current > A/memory.high
> 2. A/B/memory.current < A/B/memory.low
> 3. A/C/memory.current >= A/C/memory.low
>
> As 'A' is high, i.e. triggers reclaim from 'A', and 'B' is low, we
> should reclaim from 'C' until 'A' is no longer high or until we can
> no longer reclaim from 'C'. If 'A', i.e. @root, isn't excluded by
> mem_cgroup_low when reclaming from 'A', then 'B' won't be considered
> low and we will reclaim indiscriminately from both 'B' and 'C'.
>
> Signed-off-by: Sean Christopherson <sean.j.christopherson@intel.com>
> ---
> mm/memcontrol.c | 50 ++++++++++++++++++++++++++++++++------------------
> 1 file changed, 32 insertions(+), 18 deletions(-)
Good catch, wonder why it hasn't been reported before.
IMO the patch looks good - it makes the mem_cgroup_low()
code easier to follow.
Acked-by: Vladimir Davydov <vdavydov.dev@gmail.com>
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next prev parent reply other threads:[~2017-06-03 19:15 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-06-02 20:13 [PATCH] mm/memcontrol: exclude @root from checks in mem_cgroup_low Sean Christopherson
2017-06-02 20:22 ` Christopherson, Sean J
2017-06-03 19:15 ` Vladimir Davydov [this message]
2017-06-05 6:45 ` Balbir Singh
2017-06-05 15:16 ` Johannes Weiner
2017-06-06 10:29 ` Michal Hocko
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