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Subject[PATCH 1/2] vmscan: fix initial shrinker size handling
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Shrinker function can returns -1, it means it cannot do anything without a risk of deadlock.
For example prune_super() do this if it cannot grab superblock refrence, even if nr_to_scan=0.
Currenly we interpret this like ULONG_MAX size shrinker, evaluate total_scan according this,
and next time this shrinker can get really big pressure. Let's skip such shrinkers instead.

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

Signed-off-by: Konstantin Khlebnikov <khlebnikov@openvz.org>
---
mm/vmscan.c | 9 ++++++---
1 files changed, 6 insertions(+), 3 deletions(-)
diff --git a/mm/vmscan.c b/mm/vmscan.c
index 29b3612..f174561 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -248,14 +248,18 @@ 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
@@ -266,7 +270,6 @@ 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);


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