Re: Make vmstat deferrable again (was Re: [PATCH] mm,vmscan: Use accurate values for zone_reclaimable() checks)

[Sergey Senozhatsky <sergey.senozhatsky@gmail.com>]

On (10/23/15 06:43), Christoph Lameter wrote:
> Is this ok?

kernel/sched/loadavg.c: In function a??calc_load_enter_idlea??:
kernel/sched/loadavg.c:195:2: error: implicit declaration of function a??quiet_vmstata?? [-Werror=implicit-function-declaration]
  quiet_vmstat();
    ^

> Subject: Fix vmstat: make vmstat_updater deferrable again and shut down on idle
> 
> Currently the vmstat updater is not deferrable as a result of commit
> ba4877b9ca51f80b5d30f304a46762f0509e1635. This in turn can cause multiple
> interruptions of the applications because the vmstat updater may run at
> different times than tick processing. No good.
> 
> Make vmstate_update deferrable again and provide a function that
> shuts down the vmstat updater when we go idle by folding the differentials.
> Shut it down from the load average calculation logic introduced by nohz.
> 
> Note that the shepherd thread will continue scanning the differentials
> from another processor and will reenable the vmstat workers if it
> detects any changes.
> 
> Fixes: ba4877b9ca51f80b5d30f304a46762f0509e1635 (do not use deferrable delay)
> Signed-off-by: Christoph Lameter <cl@linux.com>
> 
> Index: linux/mm/vmstat.c
> ===================================================================
> --- linux.orig/mm/vmstat.c
> +++ linux/mm/vmstat.c
> @@ -1395,6 +1395,20 @@ static void vmstat_update(struct work_st
>  }
> 
>  /*
> + * Switch off vmstat processing and then fold all the remaining differentials
> + * until the diffs stay at zero. The function is used by NOHZ and can only be
> + * invoked when tick processing is not active.
> + */
> +void quiet_vmstat(void)
> +{
> +	do {
> +		if (!cpumask_test_and_set_cpu(smp_processor_id(), cpu_stat_off))
> +			cancel_delayed_work(this_cpu_ptr(&vmstat_work));

shouldn't preemption be disable for smp_processor_id() here?

	-ss

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