linux-kernel - Re: [PATCH 08/10] mm: deactivations shouldn't bias the LRU balance

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Message-ID: <20160608081515.GD28620@bbox>
Date:	Wed, 8 Jun 2016 17:15:15 +0900
From:	Minchan Kim <minchan@...nel.org>
To:	Johannes Weiner <hannes@...xchg.org>
CC:	<linux-mm@...ck.org>, <linux-kernel@...r.kernel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Rik van Riel <riel@...hat.com>, Mel Gorman <mgorman@...e.de>,
	Andrea Arcangeli <aarcange@...hat.com>,
	Andi Kleen <andi@...stfloor.org>,
	Michal Hocko <mhocko@...e.cz>,
	Tim Chen <tim.c.chen@...ux.intel.com>, <kernel-team@...com>
Subject: Re: [PATCH 08/10] mm: deactivations shouldn't bias the LRU balance

On Mon, Jun 06, 2016 at 03:48:34PM -0400, Johannes Weiner wrote:
> Operations like MADV_FREE, FADV_DONTNEED etc. currently move any
> affected active pages to the inactive list to accelerate their reclaim
> (good) but also steer page reclaim toward that LRU type, or away from
> the other (bad).
> 
> The reason why this is undesirable is that such operations are not
> part of the regular page aging cycle, and rather a fluke that doesn't
> say much about the remaining pages on that list. They might all be in
> heavy use. But once the chunk of easy victims has been purged, the VM
> continues to apply elevated pressure on the remaining hot pages. The
> other LRU, meanwhile, might have easily reclaimable pages, and there
> was never a need to steer away from it in the first place.
> 
> As the previous patch outlined, we should focus on recording actually
> observed cost to steer the balance rather than speculating about the
> potential value of one LRU list over the other. In that spirit, leave
> explicitely deactivated pages to the LRU algorithm to pick up, and let
> rotations decide which list is the easiest to reclaim.
> 
> Signed-off-by: Johannes Weiner <hannes@...xchg.org>

Nice description. Agreed.

Acked-by: Minchan Kim <minchan@...nel.org>