linux-kernel - Re: [PATCH v2 1/2] vmscan: don't subtraction of unsined

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Date:	Fri, 9 Jul 2010 10:46:32 +0900
From:	Minchan Kim <minchan.kim@...il.com>
To:	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	LKML <linux-kernel@...r.kernel.org>,
	linux-mm <linux-mm@...ck.org>, Mel Gorman <mel@....ul.ie>,
	Rik van Riel <riel@...hat.com>,
	Johannes Weiner <hannes@...xchg.org>
Subject: Re: [PATCH v2 1/2] vmscan: don't subtraction of unsined

On Fri, Jul 9, 2010 at 10:16 AM, KOSAKI Motohiro
<kosaki.motohiro@...fujitsu.com> wrote:
>
>> > @@ -2628,16 +2628,16 @@ static int __zone_reclaim(struct zone *zone, gfp_t gfp_mask, unsigned int order)
>> >              * take a long time.
>> >              */
>> >             while (shrink_slab(sc.nr_scanned, gfp_mask, order) &&
>> > -                   zone_page_state(zone, NR_SLAB_RECLAIMABLE) >
>> > -                           slab_reclaimable - nr_pages)
>> > +                  (zone_page_state(zone, NR_SLAB_RECLAIMABLE) + nr_pages > n))
>> >                     ;
>> >
>> >             /*
>> >              * Update nr_reclaimed by the number of slab pages we
>> >              * reclaimed from this zone.
>> >              */
>> > -           sc.nr_reclaimed += slab_reclaimable -
>> > -                   zone_page_state(zone, NR_SLAB_RECLAIMABLE);
>> > +           m = zone_page_state(zone, NR_SLAB_RECLAIMABLE);
>> > +           if (m < n)
>> > +                   sc.nr_reclaimed += n - m;
>>
>> And it's not a completly trivial objection.  Your patch made the above
>> code snippet quite a lot harder to read (and hence harder to maintain).
>
> Initially, I proposed following patch to Christoph. but he prefer n and m.
> To be honest, I don't think this naming is big matter. so you prefer following
> I'll submit it.
>
>
>
>
> =====================================================================
> From 397199d69860061eaa5e1aaadac45c46c76b0522 Mon Sep 17 00:00:00 2001
> From: KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>
> Date: Wed, 30 Jun 2010 13:35:16 +0900
> Subject: [PATCH] vmscan: don't subtraction of unsined
>
> 'slab_reclaimable' and 'nr_pages' are unsigned. so, subtraction is
> unsafe.
>
> Signed-off-by: KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>
Reviewed-by: Minchan Kim <minchan.kim@...il.com>

I like this than n,m.

-- 
Kind regards,
Minchan Kim
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