linux-kernel - Re: [RFC 10/10] autonuma, memory tiering: Adjust hot threshold automatically

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Message-ID: <20191101093145.GT4131@hirez.programming.kicks-ass.net>
Date:   Fri, 1 Nov 2019 10:31:45 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     "Huang, Ying" <ying.huang@...el.com>
Cc:     linux-mm@...ck.org, linux-kernel@...r.kernel.org,
        Andrew Morton <akpm@...ux-foundation.org>,
        Michal Hocko <mhocko@...e.com>, Rik van Riel <riel@...hat.com>,
        Mel Gorman <mgorman@...e.de>, Ingo Molnar <mingo@...nel.org>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Dan Williams <dan.j.williams@...el.com>,
        Fengguang Wu <fengguang.wu@...el.com>
Subject: Re: [RFC 10/10] autonuma, memory tiering: Adjust hot threshold
 automatically

On Fri, Nov 01, 2019 at 03:57:27PM +0800, Huang, Ying wrote:

> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
> index 0a83e9cf6685..22bdbb7afac2 100644
> --- a/kernel/sched/fair.c
> +++ b/kernel/sched/fair.c
> @@ -1486,6 +1486,41 @@ static bool numa_migration_check_rate_limit(struct pglist_data *pgdat,
>  	return true;
>  }
>  
> +#define NUMA_MIGRATION_ADJUST_STEPS	16
> +
> +static void numa_migration_adjust_threshold(struct pglist_data *pgdat,
> +					    unsigned long rate_limit,
> +					    unsigned long ref_threshold)
> +{
> +	unsigned long now = jiffies, last_threshold_jiffies;
> +	unsigned long unit_threshold, threshold;
> +	unsigned long try_migrate, ref_try_migrate, mdiff;
> +
> +	last_threshold_jiffies = pgdat->autonuma_threshold_jiffies;
> +	if (now > last_threshold_jiffies +
> +	    msecs_to_jiffies(sysctl_numa_balancing_scan_period_max) &&
> +	    cmpxchg(&pgdat->autonuma_threshold_jiffies,
> +		    last_threshold_jiffies, now) == last_threshold_jiffies) {

That is seriously unreadable gunk.

> +
> +		ref_try_migrate = rate_limit *
> +			sysctl_numa_balancing_scan_period_max / 1000;
> +		try_migrate = node_page_state(pgdat, NUMA_TRY_MIGRATE);
> +		mdiff = try_migrate - pgdat->autonuma_threshold_try_migrate;
> +		unit_threshold = ref_threshold / NUMA_MIGRATION_ADJUST_STEPS;
> +		threshold = pgdat->autonuma_threshold;
> +		if (!threshold)
> +			threshold = ref_threshold;
> +		if (mdiff > ref_try_migrate * 11 / 10)
> +			threshold = max(threshold - unit_threshold,
> +					unit_threshold);
> +		else if (mdiff < ref_try_migrate * 9 / 10)
> +			threshold = min(threshold + unit_threshold,
> +					ref_threshold);

And that is violating codingstyle.

> +		pgdat->autonuma_threshold_try_migrate = try_migrate;
> +		pgdat->autonuma_threshold = threshold;
> +	}
> +}


Maybe if you use variable names that are slightly shorter than half your
line length?