Date:   Thu, 25 Jul 2019 10:33:10 +0800
From:   王贇 <yun.wang@...ux.alibaba.com>
To:     Peter Zijlstra <peterz@...radead.org>, hannes@...xchg.org,
        mhocko@...nel.org, vdavydov.dev@...il.com,
        Ingo Molnar <mingo@...hat.com>
Cc:     linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        mcgrof@...nel.org, keescook@...omium.org,
        linux-fsdevel@...r.kernel.org, cgroups@...r.kernel.org,
        Michal Koutný <mkoutny@...e.com>,
        Hillf Danton <hdanton@...a.com>
Subject: Re: [PATCH v2 0/4] per-cgroup numa suite

Hi, Peter

Now we have all these stuff in cpu cgroup, with the new statistic
folks should be able to estimate their per-cgroup workloads on
numa platform, and numa group + cling would help to address the
issue when their workloads can't be settled on one node.

How do you think about this version :-)

Regards,
Michael Wang

On 2019/7/16 上午11:38, 王贇 wrote:
> During our torturing on numa stuff, we found problems like:
> 
>   * missing per-cgroup information about the per-node execution status
>   * missing per-cgroup information about the numa locality
> 
> That is when we have a cpu cgroup running with bunch of tasks, no good
> way to tell how it's tasks are dealing with numa.
> 
> The first two patches are trying to complete the missing pieces, but
> more problems appeared after monitoring these status:
> 
>   * tasks not always running on the preferred numa node
>   * tasks from same cgroup running on different nodes
> 
> The task numa group handler will always check if tasks are sharing pages
> and try to pack them into a single numa group, so they will have chance to
> settle down on the same node, but this failed in some cases:
> 
>   * workloads share page caches rather than share mappings
>   * workloads got too many wakeup across nodes
> 
> Since page caches are not traced by numa balancing, there are no way to
> realize such kind of relationship, and when there are too many wakeup,
> task will be drag from the preferred node and then migrate back by numa
> balancing, repeatedly.
> 
> Here the third patch try to address the first issue, we could now give hint
> to kernel about the relationship of tasks, and pack them into single numa
> group.
> 
> And the forth patch introduced numa cling, which try to address the wakup
> issue, now we try to make task stay on the preferred node on wakeup in fast
> path, in order to address the unbalancing risk, we monitoring the numa
> migration failure ratio, and pause numa cling when it reach the specified
> degree.
> 
> Since v1:
>   * move statistics from memory cgroup into cpu group
>   * statistics now accounting in hierarchical way
>   * locality now accounted into 8 regions equally
>   * numa cling no longer override select_idle_sibling, instead we
>     prevent numa swap migration with tasks cling to dst-node, also
>     prevent wake affine to drag tasks away which already cling to
>     prev-cpu
>   * other refine on comments and names
> 
> Michael Wang (4):
>   v2 numa: introduce per-cgroup numa balancing locality statistic
>   v2 numa: append per-node execution time in cpu.numa_stat
>   v2 numa: introduce numa group per task group
>   v4 numa: introduce numa cling feature
> 
>  include/linux/sched.h        |   8 +-
>  include/linux/sched/sysctl.h |   3 +
>  kernel/sched/core.c          |  85 ++++++++
>  kernel/sched/debug.c         |   7 +
>  kernel/sched/fair.c          | 510 ++++++++++++++++++++++++++++++++++++++++++-
>  kernel/sched/sched.h         |  41 ++++
>  kernel/sysctl.c              |   9 +
>  7 files changed, 651 insertions(+), 12 deletions(-)
> 

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