linux-kernel - Re: [RFC 4/6] mm, thp: move collapsing from khugepaged to task

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Message-ID: <20150223142514.GX5029@twins.programming.kicks-ass.net>
Date:	Mon, 23 Feb 2015 15:25:14 +0100
From:	Peter Zijlstra <peterz@...radead.org>
To:	Vlastimil Babka <vbabka@...e.cz>
Cc:	linux-mm@...ck.org, linux-kernel@...r.kernel.org,
	Andrew Morton <akpm@...ux-foundation.org>,
	Hugh Dickins <hughd@...gle.com>,
	Andrea Arcangeli <aarcange@...hat.com>,
	"Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
	Rik van Riel <riel@...hat.com>, Mel Gorman <mgorman@...e.de>,
	Michal Hocko <mhocko@...e.cz>,
	Ebru Akagunduz <ebru.akagunduz@...il.com>,
	Alex Thorlton <athorlton@....com>,
	David Rientjes <rientjes@...gle.com>,
	Ingo Molnar <mingo@...nel.org>
Subject: Re: [RFC 4/6] mm, thp: move collapsing from khugepaged to task_work
 context

On Mon, Feb 23, 2015 at 01:58:40PM +0100, Vlastimil Babka wrote:
> @@ -7713,8 +7820,15 @@ static void task_tick_fair(struct rq *rq, struct task_struct *curr, int queued)
>  		entity_tick(cfs_rq, se, queued);
>  	}
>  
> -	if (numabalancing_enabled)
> -		task_tick_numa(rq, curr);
> +	/*
> +	 * For latency considerations, don't schedule the THP work together
> +	 * with NUMA work. NUMA has higher priority, assuming remote accesses
> +	 * have worse penalty than TLB misses.
> +	 */
> +	if (!(numabalancing_enabled && task_tick_numa(rq, curr))
> +						&& khugepaged_enabled())
> +		task_tick_thp(rq, curr);
> +
>  
>  	update_rq_runnable_avg(rq, 1);
>  }

That's a bit yucky; and I think there's no problem moving that
update_rq_runnable_avg() thing up a bit; which would get you:

static void task_tick_fair(..)
{

	...

	update_rq_runnable_avg();

	if (numabalancing_enabled && task_tick_numa(rq, curr))
		return;

	if (khugepaged_enabled() && task_tick_thp(rq, curr))
		return;
}

Clearly the return on that second conditional is a tad pointless, but
OCD :-)
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