linux-kernel - Re: [patch 6/8] mm: vmscan: clean up get_scan

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Message-ID: <20121213110759.GA1009@suse.de>
Date:	Thu, 13 Dec 2012 11:07:59 +0000
From:	Mel Gorman <mgorman@...e.de>
To:	Johannes Weiner <hannes@...xchg.org>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Rik van Riel <riel@...hat.com>,
	Michal Hocko <mhocko@...e.cz>, Hugh Dickins <hughd@...gle.com>,
	linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: Re: [patch 6/8] mm: vmscan: clean up get_scan_count()

On Wed, Dec 12, 2012 at 04:43:38PM -0500, Johannes Weiner wrote:
> Reclaim pressure balance between anon and file pages is calculated
> through a tuple of numerators and a shared denominator.
> 
> Exceptional cases that want to force-scan anon or file pages configure
> the numerators and denominator such that one list is preferred, which
> is not necessarily the most obvious way:
> 
>     fraction[0] = 1;
>     fraction[1] = 0;
>     denominator = 1;
>     goto out;
> 
> Make this easier by making the force-scan cases explicit and use the
> fractionals only in case they are calculated from reclaim history.
> 
> And bring the variable declarations/definitions in order.
> 
> Signed-off-by: Johannes Weiner <hannes@...xchg.org>

Acked-by: Mel Gorman <mgorman@...e.de>

The if at the end looks like it should have been a switch maybe?

switch(scan_balance) {
case SCAN_EQUAL:
	/* Scan relative to size */
	break;
case SCAN_FRACT:
	/* Scan proportional to swappiness */
	scan = div64_u64(scan * fraction[file], denominator);
case SCAN_FILE:
case SCAN_ANON:
	/* Scan only file or only anon LRU */
	if ((scan_balance == SCAN_FILE) != file)
		scan = 0;
	break;
default:
	/* Look ma, no brain */
	BUG();
}

-- 
Mel Gorman
SUSE Labs
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