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SubjectRe: [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@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.

> > - 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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