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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>,
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> On Thu, 24 Mar 2011 11:48:19 +0900 (JST) KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com> wrote:
> 
> > > 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?
> 
> The part which isn't there: how does the kernel now address the problem
> which that code fixed?

Ah, got it.
The history says the problem haven't occur for three years. thus I
meant

past: code exist, but broken and don't work for three years.
new:  code removed.

What's different? But last minchan's mail pointed out recent
drain_all_pages() stuff depend on a return value of try_to_free_pages.

thus, I've made new patch and sent it. please see it?