From d460acb5bdffc19b492b70b8f416c24dc03c474e Mon Sep 17 00:00:00 2001 From: Chris Wilson Date: Wed, 6 Sep 2017 16:19:26 -0700 Subject: [PATCH] mm: track actual nr_scanned during shrink_slab() Some shrinkers may only be able to free a bunch of objects at a time, and so free more than the requested nr_to_scan in one pass. Whilst other shrinkers may find themselves even unable to scan as many objects as they counted, and so underreport. Account for the extra freed/scanned objects against the total number of objects we intend to scan, otherwise we may end up penalising the slab far more than intended. Similarly, we want to add the underperforming scan to the deferred pass so that we try harder and harder in future passes. Link: http://lkml.kernel.org/r/20170822135325.9191-1-chris@chris-wilson.co.uk Signed-off-by: Chris Wilson Cc: Michal Hocko Cc: Johannes Weiner Cc: Hillf Danton Cc: Minchan Kim Cc: Vlastimil Babka Cc: Mel Gorman Cc: Shaohua Li Cc: Christoph Lameter Cc: Pekka Enberg Cc: David Rientjes Cc: Joonsoo Kim Cc: Joonas Lahtinen Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- include/linux/shrinker.h | 7 +++++++ mm/vmscan.c | 7 ++++--- 2 files changed, 11 insertions(+), 3 deletions(-) diff --git a/include/linux/shrinker.h b/include/linux/shrinker.h index 4fcacd915d45..51d189615bda 100644 --- a/include/linux/shrinker.h +++ b/include/linux/shrinker.h @@ -18,6 +18,13 @@ struct shrink_control { */ unsigned long nr_to_scan; + /* + * How many objects did scan_objects process? + * This defaults to nr_to_scan before every call, but the callee + * should track its actual progress. + */ + unsigned long nr_scanned; + /* current node being shrunk (for NUMA aware shrinkers) */ int nid; diff --git a/mm/vmscan.c b/mm/vmscan.c index f957afe900ec..095817820a56 100644 --- a/mm/vmscan.c +++ b/mm/vmscan.c @@ -393,14 +393,15 @@ static unsigned long do_shrink_slab(struct shrink_control *shrinkctl, unsigned long nr_to_scan = min(batch_size, total_scan); shrinkctl->nr_to_scan = nr_to_scan; + shrinkctl->nr_scanned = nr_to_scan; ret = shrinker->scan_objects(shrinker, shrinkctl); if (ret == SHRINK_STOP) break; freed += ret; - count_vm_events(SLABS_SCANNED, nr_to_scan); - total_scan -= nr_to_scan; - scanned += nr_to_scan; + count_vm_events(SLABS_SCANNED, shrinkctl->nr_scanned); + total_scan -= shrinkctl->nr_scanned; + scanned += shrinkctl->nr_scanned; cond_resched(); }