linux-kernel - Re: [patch V3 0/8] extensible prctl task isolation interface and vmstat sync

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Date:   Wed, 25 Aug 2021 07:02:21 -0300
From:   Marcelo Tosatti <mtosatti@...hat.com>
To:     linux-kernel@...r.kernel.org
Cc:     Nitesh Lal <nilal@...hat.com>,
        Nicolas Saenz Julienne <nsaenzju@...hat.com>,
        Frederic Weisbecker <frederic@...nel.org>,
        Christoph Lameter <cl@...ux.com>,
        Juri Lelli <juri.lelli@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Alex Belits <abelits@...its.com>, Peter Xu <peterx@...hat.com>,
        Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [patch V3 0/8] extensible prctl task isolation interface and
 vmstat sync


+CC Thomas.

On Tue, Aug 24, 2021 at 12:24:23PM -0300, Marcelo Tosatti wrote:
> 
> The logic to disable vmstat worker thread, when entering
> nohz full, does not cover all scenarios. For example, it is possible
> for the following to happen:
> 
> 1) enter nohz_full, which calls refresh_cpu_vm_stats, syncing the stats.
> 2) app runs mlock, which increases counters for mlock'ed pages.
> 3) start -RT loop
> 
> Since refresh_cpu_vm_stats from nohz_full logic can happen _before_
> the mlock, vmstat shepherd can restart vmstat worker thread on
> the CPU in question.
> 
> To fix this, add task isolation prctl interface to quiesce
> deferred actions when returning to userspace.
> 
> The patchset is based on ideas and code from the 
> task isolation patchset from Alex Belits:
> https://lwn.net/Articles/816298/
> 
> Please refer to Documentation/userspace-api/task_isolation.rst
> (patch 2) for details.
> 
> Note: the prctl interface is independent of nohz_full=.
> 
> ---------
> 
> v3: 
> 
>  - Split in smaller patches		 (Nitesh Lal).
>  - Misc cleanups			 (Nitesh Lal).
>  - Clarify nohz_full is not a dependency (Nicolas Saenz).
>  - Incorrect values for prctl definitions (kernel robot).
>  - Save configured state, so applications  
>    can activate externally configured
>    task isolation parameters.
>  - Remove "system default" notion (chisol should
>    make it obsolete).
>  - Update documentation: add new section with explanation
>    about configuration/activation and code example.
>  - Update samples.
>  - Report configuration/activation state at
>    /proc/pid/task_isolation.
>  - Condense dirty information of per-CPU vmstats counters 
>    in a bool.
>  - In-kernel KVM support.
>  - Add support to configure inheritance on fork and exec.
> 
> v2:
> 
> - Finer-grained control of quiescing (Frederic Weisbecker / Nicolas Saenz).
> 
> - Avoid potential regressions by allowing applications
>   to use ISOL_F_QUIESCE_DEFMASK (whose default value
>   is configurable in /sys/).         (Nitesh Lal / Nicolas Saenz).
> 
> v2 can be found at:
> https://lore.kernel.org/patchwork/project/lkml/list/?series=510225
> 
> 
> ---
> 
>  Documentation/userspace-api/task_isolation.rst |  281 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
>  arch/x86/kvm/x86.c                             |    3 
>  fs/proc/base.c                                 |   68 +++++++++++++++++++
>  include/linux/sched.h                          |    5 +
>  include/linux/task_isolation.h                 |  131 ++++++++++++++++++++++++++++++++++++++
>  include/linux/vmstat.h                         |   17 ++++
>  include/uapi/linux/prctl.h                     |   27 +++++++
>  init/init_task.c                               |    3 
>  kernel/Makefile                                |    2 
>  kernel/entry/common.c                          |    2 
>  kernel/exit.c                                  |    2 
>  kernel/fork.c                                  |   23 ++++++
>  kernel/sys.c                                   |   26 +++++++
>  kernel/task_isolation.c                        |  315 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
>  mm/vmstat.c                                    |  167 ++++++++++++++++++++++++++++++++++++------------
>  samples/Kconfig                                |    7 ++
>  samples/Makefile                               |    1 
>  samples/task_isolation/Makefile                |    9 ++
>  samples/task_isolation/task_isol.c             |   83 ++++++++++++++++++++++++
>  samples/task_isolation/task_isol.h             |    9 ++
>  samples/task_isolation/task_isol_userloop.c    |   56 ++++++++++++++++
>  21 files changed, 1194 insertions(+), 43 deletions(-)
> 
>