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

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Message-ID: <bcef7a38-7c60-0949-3d3b-1462638a5d4c@oracle.com>
Date:   Tue, 19 Jan 2021 06:13:57 +1100
From:   Imran Khan <imran.f.khan@...cle.com>
To:     Mel Gorman <mgorman@...e.de>
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 18/1/21 9:57 pm, Mel Gorman wrote:
> 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.
> 

Okay, understood. Thanks for clarifying.