linux-kernel - Re: [patch 3/5] mm: vmstat: optionally flush per-CPU vmstat counters on return to userspace

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Message-ID: <alpine.DEB.2.22.394.2107121056560.409981@gentwo.de>
Date:   Mon, 12 Jul 2021 11:05:58 +0200 (CEST)
From:   Christoph Lameter <cl@...two.de>
To:     Marcelo Tosatti <mtosatti@...hat.com>
cc:     linux-kernel@...r.kernel.org, Thomas Gleixner <tglx@...utronix.de>,
        Frederic Weisbecker <frederic@...nel.org>,
        Juri Lelli <juri.lelli@...hat.com>,
        Nitesh Lal <nilal@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Nicolas Saenz <nsaenzju@...hat.com>
Subject: Re: [patch 3/5] mm: vmstat: optionally flush per-CPU vmstat counters
 on return to userspace

On Fri, 9 Jul 2021, Marcelo Tosatti wrote:

> +
> +	if (!static_branch_unlikely(&vmstat_sync_enabled))
> +		return;
> +
> +	cpu = smp_processor_id();
> +
> +	if (housekeeping_cpu(cpu, HK_FLAG_QUIESCE_URET))
> +		return;
> +
> +	per_cpu(vmstat_dirty, smp_processor_id()) = true;
> +}

And you are going to insert this into all the performance critical VM
statistics handling. Inline?

And why do you need to do such things as to determine the processor? At
mininum do this using this cpu operations like the vmstat functions
currently do. And, lucky us, now we also have
more issues why we should disable preemption etc etc while handling vm
counters.