gregkh at linuxfoundation
Jul 30, 2012, 10:31 AM
Post #1 of 1
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[ 41/41] vmscan: fix initial shrinker size handling
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From: Greg KH <gregkh [at] linuxfoundation>
3.0-stable review patch. If anyone has any objections, please let me know.
------------------
From: Konstantin Khlebnikov <khlebnikov [at] openvz>
commit 635697c663f38106063d5659f0cf2e45afcd4bb5 upstream.
Stable note: The commit [acf92b48: vmscan: shrinker->nr updates race and
go wrong] aimed to reduce excessive reclaim of slab objects but
had bug in how it treated shrinker functions that returned -1.
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 <khlebnikov [at] openvz>
Cc: Dave Chinner <david [at] fromorbit>
Signed-off-by: Andrew Morton <akpm [at] linux-foundation>
Signed-off-by: Linus Torvalds <torvalds [at] linux-foundation>
Signed-off-by: Mel Gorman <mgorman [at] suse>
Signed-off-by: Greg Kroah-Hartman <gregkh [at] linuxfoundation>
---
mm/vmscan.c | 9 ++++++---
1 file changed, 6 insertions(+), 3 deletions(-)
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -248,12 +248,16 @@ unsigned long shrink_slab(struct 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;
+ 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
@@ -264,7 +268,6 @@ unsigned long shrink_slab(struct 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);
--
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