linux-kernel - [patch 0/5] optionally sync per-CPU vmstats counter on return to userspace

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Message-ID: <20210701210336.358118649@fuller.cnet>
Date:   Thu, 01 Jul 2021 18:03:36 -0300
From:   Marcelo Tosatti <mtosatti@...hat.com>
To:     linux-kernel@...r.kernel.org
Cc:     Christoph Lameter <cl@...ux.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Frederic Weisbecker <frederic@...nel.org>,
        Juri Lelli <juri.lelli@...hat.com>,
        Nitesh Lal <nilal@...hat.com>
Subject: [patch 0/5] optionally sync per-CPU vmstats counter on return to userspace

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, optionally sync the vmstat counters when returning
from userspace, controllable by a new "vmstat_sync" isolcpus
flags (default off).

See individual patches for details.