Messages in this thread | | | Date | Thu, 15 Jul 2010 12:15:51 -0700 | From | Andrew Morton <> | Subject | Re: [PATCH v2 2/2] vmscan: shrink_slab() require number of lru_pages, not page order |
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On Tue, 13 Jul 2010 14:41:28 +0900 (JST) KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com> wrote:
> Now, shrink_slab() has following scanning equation. > > lru_scanned max_pass > basic_scan_objects = 4 x ------------- x ----------------------------- > lru_pages shrinker->seeks (default:2) > > scan_objects = min(basic_scan_objects, max_pass * 2) > > Then, If we pass very small value as lru_pages instead real number of > lru pages, shrink_slab() drop much objects rather than necessary. and > now, __zone_reclaim() pass 'order' as lru_pages by mistake. that makes > bad result. > > Example, If we receive very low memory pressure (scan = 32, order = 0), > shrink_slab() via zone_reclaim() always drop _all_ icache/dcache > objects. (see above equation, very small lru_pages make very big > scan_objects result) > > This patch fixes it. > > Signed-off-by: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com> > Reviewed-by: Minchan Kim <minchan.kim@gmail.com> > Acked-by: Christoph Lameter <cl@linux-foundation.org> > Acked-by: Rik van Riel <riel@redhat.com> > --- > mm/vmscan.c | 4 +++- > 1 files changed, 3 insertions(+), 1 deletions(-) > > diff --git a/mm/vmscan.c b/mm/vmscan.c > index 6ff51c0..1bf9f72 100644 > --- a/mm/vmscan.c > +++ b/mm/vmscan.c > @@ -2612,6 +2612,8 @@ static int __zone_reclaim(struct zone *zone, gfp_t gfp_mask, unsigned int order) > > nr_slab_pages0 = zone_page_state(zone, NR_SLAB_RECLAIMABLE); > if (nr_slab_pages0 > zone->min_slab_pages) { > + unsigned long lru_pages = zone_reclaimable_pages(zone); > + > /* > * shrink_slab() does not currently allow us to determine how > * many pages were freed in this zone. So we take the current > @@ -2622,7 +2624,7 @@ static int __zone_reclaim(struct zone *zone, gfp_t gfp_mask, unsigned int order) > * Note that shrink_slab will free memory on all zones and may > * take a long time. > */ > - while (shrink_slab(sc.nr_scanned, gfp_mask, order) && > + while (shrink_slab(sc.nr_scanned, gfp_mask, lru_pages) && > (zone_page_state(zone, NR_SLAB_RECLAIMABLE) + nr_pages > > nr_slab_pages0)) > ;
Wouldn't it be better to recalculate zone_reclaimable_pages() each time around the loop? For example, shrink_icache_memory()->prune_icache() will remove pagecache from an inode if it hits the tail of the list. This can change the number of reclaimable pages by squigabytes, but this code thinks nothing changed?
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