linux-kernel - Re: [PATCH 08/10] vmscan: isolated_lru_pages() stop neighbour search if neighbour cannot be isolated

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Date:	Wed, 8 Sep 2010 12:12:30 +0100
From:	Mel Gorman <mel@....ul.ie>
To:	Minchan Kim <minchan.kim@...il.com>
Cc:	linux-mm@...ck.org, linux-fsdevel@...r.kernel.org,
	Linux Kernel List <linux-kernel@...r.kernel.org>,
	Rik van Riel <riel@...hat.com>,
	Johannes Weiner <hannes@...xchg.org>,
	Wu Fengguang <fengguang.wu@...el.com>,
	Andrea Arcangeli <aarcange@...hat.com>,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	Dave Chinner <david@...morbit.com>,
	Chris Mason <chris.mason@...cle.com>,
	Christoph Hellwig <hch@....de>,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH 08/10] vmscan: isolated_lru_pages() stop neighbour
	search if neighbour cannot be isolated

On Wed, Sep 08, 2010 at 12:37:08AM +0900, Minchan Kim wrote:
> On Mon, Sep 06, 2010 at 11:47:31AM +0100, Mel Gorman wrote:
> > From: KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>
> > 
> > isolate_lru_pages() does not just isolate LRU tail pages, but also isolate
> > neighbour pages of the eviction page. The neighbour search does not stop even
> > if neighbours cannot be isolated which is excessive as the lumpy reclaim will
> > no longer result in a successful higher order allocation. This patch stops
> > the PFN neighbour pages if an isolation fails and moves on to the next block.
> > 
> > Signed-off-by: KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>
> > Signed-off-by: Mel Gorman <mel@....ul.ie>
> > ---
> >  mm/vmscan.c |   24 ++++++++++++++++--------
> >  1 files changed, 16 insertions(+), 8 deletions(-)
> > 
> > diff --git a/mm/vmscan.c b/mm/vmscan.c
> > index 64f9ca5..ff52b46 100644
> > --- a/mm/vmscan.c
> > +++ b/mm/vmscan.c
> > @@ -1047,14 +1047,18 @@ static unsigned long isolate_lru_pages(unsigned long nr_to_scan,
> >  				continue;
> >  
> >  			/* Avoid holes within the zone. */
> > -			if (unlikely(!pfn_valid_within(pfn)))
> > +			if (unlikely(!pfn_valid_within(pfn))) {
> > +				nr_lumpy_failed++;
> >  				break;
> > +			}
> >  
> >  			cursor_page = pfn_to_page(pfn);
> >  
> >  			/* Check that we have not crossed a zone boundary. */
> > -			if (unlikely(page_zone_id(cursor_page) != zone_id))
> > -				continue;
> > +			if (unlikely(page_zone_id(cursor_page) != zone_id)) {
> > +				nr_lumpy_failed++;
> > +				break;
> > +			}
> >  
> >  			/*
> >  			 * If we don't have enough swap space, reclaiming of
> > @@ -1062,8 +1066,10 @@ static unsigned long isolate_lru_pages(unsigned long nr_to_scan,
> >  			 * pointless.
> >  			 */
> >  			if (nr_swap_pages <= 0 && PageAnon(cursor_page) &&
> > -					!PageSwapCache(cursor_page))
> > -				continue;
> > +			    !PageSwapCache(cursor_page)) {
> > +				nr_lumpy_failed++;
> > +				break;
> > +			}
> >  
> >  			if (__isolate_lru_page(cursor_page, mode, file) == 0) {
> >  				list_move(&cursor_page->lru, dst);
> > @@ -1074,9 +1080,11 @@ static unsigned long isolate_lru_pages(unsigned long nr_to_scan,
> >  					nr_lumpy_dirty++;
> >  				scan++;
> >  			} else {
> > -				if (mode == ISOLATE_BOTH &&
> 
> Why can we remove ISOLATION_BOTH check?

Because this is lumpy reclaim and whether we are isolating inactive, active
or both doesn't matter. The fact we failed to isolate the page and it has
a reference count means that a contiguous allocation in that area will fail.

> Is it a intentionall behavior change?
> 

Yes.

> > -						page_count(cursor_page))
> > -					nr_lumpy_failed++;
> > +				/* the page is freed already. */
> > +				if (!page_count(cursor_page))
> > +					continue;
> > +				nr_lumpy_failed++;
> > +				break;
> >  			}
> >  		}
> >  	}

-- 
Mel Gorman
Part-time Phd Student                          Linux Technology Center
University of Limerick                         IBM Dublin Software Lab
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