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

[Minchan Kim <minchan.kim@gmail.com>]

On Wed, Sep 08, 2010 at 12:12:30PM +0100, Mel Gorman wrote:
> 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@jp.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@jp.fujitsu.com>
> > > Signed-off-by: Mel Gorman <mel@csn.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.

It looks good to me. 
Reviewed-by: Minchan Kim <minchan.kim@gmail.com>

-- 
Kind regards,
Minchan Kim