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

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Date:	Tue, 29 Jun 2010 10:14:35 -0500 (CDT)
From:	Christoph Lameter <cl@...ux-foundation.org>
To:	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>
cc:	LKML <linux-kernel@...r.kernel.org>, linux-mm <linux-mm@...ck.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Mel Gorman <mel@....ul.ie>, Rik van Riel <riel@...hat.com>,
	Minchan Kim <minchan.kim@...il.com>,
	Johannes Weiner <hannes@...xchg.org>
Subject: Re: [PATCH 2/2] vmscan: don't subtraction of unsined 

On Mon, 28 Jun 2010, KOSAKI Motohiro wrote:

> It's unsigned. negative mean very big value. so
>
> "zone_page_state(zone, NR_SLAB_RECLAIMABLE) > slab_reclaimable - nr_pages)" will
> be evaluated false.

There were some suggestions on how to address this later in the patch.

> ok, your mysterious 'order' parameter (as pointed [1/2]) almostly prevent this case.
> because passing 'order' makes very heavy slab pressure and it avoid negative occur.
>
> but unnaturall coding style can make confusing to reviewers. ya, it's not
> big issue. but I also don't find no fixing reason.

This is not a coding issue but one of logic. The order parameter is
mysterious to me too. So is the lru_pages logic.

> > The comparison could be a problem here. So
> >
> > 			zone_page_state(zone, NR_SLAB_RECLAIMABLE) + nr_pages >
> > 				slab_reclaimable
> >
> > ?
>
> My patch take the same thing. but It avoided two line comparision.
> Do you mean you like this style? (personally, I don't). If so, I'll
> repost this patch.

Yes. I also do not like long cryptic names for local variables.
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