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Date: Thu, 7 Jul 2016 10:56:13 +0100
From: Mel Gorman <mgorman@techsingularity.net>
Subject: Re: [PATCH 08/31] mm, vmscan: simplify the logic deciding whether
 kswapd sleeps
Message-ID: <20160707095613.GQ11498@techsingularity.net>
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To: Minchan Kim <minchan@kernel.org>
Cc: Andrew Morton <akpm@linux-foundation.org>, Linux-MM <linux-mm@kvack.org>, Rik van Riel <riel@surriel.com>, Vlastimil Babka <vbabka@suse.cz>, Johannes Weiner <hannes@cmpxchg.org>, LKML <linux-kernel@vger.kernel.org>

On Thu, Jul 07, 2016 at 02:51:21PM +0900, Minchan Kim wrote:
> > It becomes difficult to tell the difference between "no wakeup and init to
> > zone 0" and "wakeup and reclaim for zone 0". At least that's the problem
> > I ran into when I tried before settling on -1.
> 
> Sorry for bothering you several times. I cannot parse what you mean.
> I didn't mean -1 is problem here but why do we need below two lines
> I removed?
> 

What you have should be fine. The hazard initially was that both
classzone_idx and kswapd_classzone_idx are enum and the signedness of
enum is implementation-dependent. Using max_t avoids that but it's a
subtle. I prefer the  obvious check of kswapd_classzone_idx == 1 because
it is clearer that we're checking for an initialised value instead of
depending on a side-effect of the casting in max_t to do the right thing.

I can apply it if you wish, I just don't think it helps.

-- 
Mel Gorman
SUSE Labs

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