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From: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
To: Andrew Morton <akpm@linux-foundation.org>
Subject: Re: [PATCH 1/5] vmscan: remove all_unreclaimable check from direct reclaim path completely
Cc: kosaki.motohiro@jp.fujitsu.com, Minchan Kim <minchan.kim@gmail.com>,
        linux-kernel@vger.kernel.org, David Rientjes <rientjes@google.com>,
        Linus Torvalds <torvalds@linux-foundation.org>,
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        Hugh Dickins <hughd@google.com>,
        KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>,
        Nick Piggin <npiggin@kernel.dk>, Johannes Weiner <hannes@cmpxchg.org>
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Date: Thu, 24 Mar 2011 11:48:19 +0900 (JST)
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> On Thu, 24 Mar 2011 11:11:46 +0900 (JST) KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com> wrote:
> 
> > Subject: [PATCH] vmscan: remove all_unreclaimable check from direct reclaim path completely
> 
> zone.all_unreclaimable is there to prevent reclaim from wasting CPU
> cycles scanning a zone which has no reclaimable pages.  When originally
> implemented it did this very well.
>
> That you guys keep breaking it, or don't feel like improving it is not a
> reason to remove it!
> 
> If the code is unneeded and the kernel now reliably solves this problem
> by other means then this should have been fully explained in the
> changelog, but it was not even mentioned.

The changelog says, the logic was removed at 2008. three years ago.
even though it's unintentionally. and I and minchan tried to resurrect
the broken logic and resurrected a bug in the logic too. then, we
are discussed it should die or alive.

Which part is hard to understand for you?