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Subject: Re: [patch 1/3] vmscan: factor out page reference checks
From: Minchan Kim <minchan.kim@gmail.com>
To: Johannes Weiner <hannes@cmpxchg.org>
Cc: Andrew Morton <akpm@linux-foundation.org>,
       KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>,
       Rik van Riel <riel@redhat.com>, linux-mm@kvack.org,
       linux-kernel@vger.kernel.org
In-Reply-To: <20100223142158.GA29762@cmpxchg.org>
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Date: Tue, 23 Feb 2010 23:44:14 +0900
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On Tue, 2010-02-23 at 15:21 +0100, Johannes Weiner wrote:
> Hello Minchan,
> 
> On Tue, Feb 23, 2010 at 10:38:23PM +0900, Minchan Kim wrote:

<snip>

> > >  
> > >  		if (PageDirty(page)) {
> > > -			if (sc->order <= PAGE_ALLOC_COSTLY_ORDER && referenced)
> > > +			if (references == PAGEREF_RECLAIM_CLEAN)
> > 
> > How equal PAGEREF_RECLAIM_CLEAN and sc->order <= PAGE_ALLOC_COSTLY_ORDER
> > && referenced by semantic?
> 
> It is encoded in page_check_references().  When
> 	sc->order <= PAGE_ALLOC_COSTLY_ORDER && referenced
> it returns PAGEREF_RECLAIM_CLEAN.
> 
> So
> 
> 	- PageDirty() && order < COSTLY && referenced
> 	+ PageDirty() && references == PAGEREF_RECLAIM_CLEAN
> 
> is an equivalent transformation.  Does this answer your question?

Hmm. I knew it. My point was PAGEREF_RECLAIM_CLEAN seems to be a little
awkward. I thought PAGEREF_RECLAIM_CLEAN means if the page was clean, it
can be reclaimed.

I think it would be better to rename it with represent "Although it's
referenced page recently, we can reclaim it if VM try to reclaim high
order page".


> 
> 	Hannes


-- 
Kind regards,
Minchan Kim