linux-kernel - Re: [PATCH 06/10] mm: remove unnecessary use-once cache bias from LRU balancing

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Message-ID: <1465266031.16365.153.camel@redhat.com>
Date:	Mon, 06 Jun 2016 22:20:31 -0400
From:	Rik van Riel <riel@...hat.com>
To:	Johannes Weiner <hannes@...xchg.org>, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	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 06/10] mm: remove unnecessary use-once cache bias from
 LRU balancing

On Mon, 2016-06-06 at 15:48 -0400, Johannes Weiner wrote:
> When the splitlru patches divided page cache and swap-backed pages
> into separate LRU lists, the pressure balance between the lists was
> biased to account for the fact that streaming IO can cause memory
> pressure with a flood of pages that are used only once. New page
> cache
> additions would tip the balance toward the file LRU, and repeat
> access
> would neutralize that bias again. This ensured that page reclaim
> would
> always go for used-once cache first.
> 
> Since e9868505987a ("mm,vmscan: only evict file pages when we have
> plenty"), page reclaim generally skips over swap-backed memory
> entirely as long as there is used-once cache present, and will apply
> the LRU balancing when only repeatedly accessed cache pages are left
> -
> at which point the previous use-once bias will have been neutralized.
> 
> This makes the use-once cache balancing bias unnecessary. Remove it.
> 

The code in get_scan_count() still seems to use the statistics
of which you just removed the updating.

What am I overlooking?

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