[PATCH] mm: vmscan: remove redundant querying to shrinker

[Heesub Shin]

shrink_slab() queries each slab cache to get the number of
elements in it. In most cases such queries are cheap but,
on some caches. For example, Android low-memory-killer,
which is operates as a slab shrinker, does relatively
long calculation once invoked and it is quite expensive.

This patch removes redundant queries to shrinker function
in the loop of shrink batch.

Signed-off-by: Heesub Shin <heesub.shin@xxxxxxxxxxx>
---
 mm/vmscan.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/mm/vmscan.c b/mm/vmscan.c
index fa6a853..11b6695 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -282,9 +282,8 @@ unsigned long shrink_slab(struct shrink_control *shrink,
 					max_pass, delta, total_scan);
 
 		while (total_scan >= batch_size) {
-			int nr_before;
+			int nr_before = max_pass;
 
-			nr_before = do_shrinker_shrink(shrinker, shrink, 0);
 			shrink_ret = do_shrinker_shrink(shrinker, shrink,
 							batch_size);
 			if (shrink_ret == -1)
@@ -293,6 +292,7 @@ unsigned long shrink_slab(struct shrink_control *shrink,
 				ret += nr_before - shrink_ret;
 			count_vm_events(SLABS_SCANNED, batch_size);
 			total_scan -= batch_size;
+			max_pass = shrink_ret;
 
 			cond_resched();
 		}
-- 
1.8.3.1

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