linux-kernel - Re: [RFC PATCH] Remove redundant sched_numa

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Message-ID: <20210118105757.GA20777@suse.de>
Date:   Mon, 18 Jan 2021 10:57:57 +0000
From:   Mel Gorman <mgorman@...e.de>
To:     Imran Khan <imran.f.khan@...cle.com>
Cc:     mingo@...hat.com, peterz@...radead.org, vincent.guittot@...aro.org,
        juri.lelli@...hat.com, dietmar.eggemann@....com,
        rostedt@...dmis.org, bsegall@...gle.com, bristot@...hat.com,
        linux-kernel@...r.kernel.org
Subject: Re: [RFC PATCH] Remove redundant sched_numa_balancing check.

On Mon, Jan 18, 2021 at 09:32:18PM +1100, Imran Khan wrote:
> task_numa_fault is invoked from do_numa_page/do_huge_pmd_numa_page,
> for task_numa_work induced memory faults. task_numa_work is scheduled
> from task_tick_numa which is invoked only if sched_numa_balancing
> is true.
> 
> So task_numa_fault will not get invoked if sched_numa_balancing is
> false and hence we can avoid checking it again in task_numa_fault.
> 
> Signed-off-by: Imran Khan <imran.f.khan@...cle.com>

If NUMA balancing is disabled at runtime, there may still be PTEs that
are marked for NUMA balancing. While these still get handled at fault,
there is no point tracking the fault information in task_numa_fault and
this function can still get called after sched_numa_balancing is
disabled.

-- 
Mel Gorman
SUSE Labs