vmscan: fix initial shrinker size handling

635697c6 · Konstantin Khlebnikov <[email protected]> · 2011-12-08 14:33:51 -08:00

A shrinker function can return -1, means that it cannot do anything
without a risk of deadlock.  For example prune_super() does this if it
cannot grab a superblock refrence, even if nr_to_scan=0.  Currently we
interpret this -1 as a ULONG_MAX size shrinker and evaluate `total_scan'
according to this.  So the next time around this shrinker can cause
really big pressure.  Let's skip such shrinkers instead.

Also make total_scan signed, otherwise the check (total_scan < 0) below
never works.

Signed-off-by: Konstantin Khlebnikov <[email protected]>
Cc: Dave Chinner <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>

Commit: 635697c663f38106063d5659f0cf2e45afcd4bb5
Parents: 09d9673d

Changes

1 files changed · +6 −3

File	Status	Add	Del	Content
mm/vmscan.c	modified	+6	−3	View file

mm/vmscan.c

View file

diff --git a/mm/vmscan.c b/mm/vmscan.c
index a1893c0..f525544 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -247,14 +247,18 @@ unsigned long shrink_slab(struct shrink_control *shrink,
 
 	list_for_each_entry(shrinker, &shrinker_list, list) {
 		unsigned long long delta;
-		unsigned long total_scan;
-		unsigned long max_pass;
+		long total_scan;
+		long max_pass;
 		int shrink_ret = 0;
 		long nr;
 		long new_nr;
 		long batch_size = shrinker->batch ? shrinker->batch
 						  : SHRINK_BATCH;
 
+		max_pass = do_shrinker_shrink(shrinker, shrink, 0);
+		if (max_pass <= 0)
+			continue;
+
 		/*
 		 * copy the current shrinker scan count into a local variable
 		 * and zero it so that other concurrent shrinker invocations
@@ -265,7 +269,6 @@ unsigned long shrink_slab(struct shrink_control *shrink,
 		} while (cmpxchg(&shrinker->nr, nr, 0) != nr);
 
 		total_scan = nr;
-		max_pass = do_shrinker_shrink(shrinker, shrink, 0);
 		delta = (4 * nr_pages_scanned) / shrinker->seeks;
 		delta *= max_pass;
 		do_div(delta, lru_pages + 1);