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vmscan: fix initial shrinker size handling

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commit 635697c663 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@openvz.org>
Cc: Dave Chinner <david@fromorbit.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Mel Gorman <mgorman@suse.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
This commit is contained in:
Konstantin Khlebnikov
2011-12-08 14:33:51 -08:00
committed by Greg Kroah-Hartman
parent ad04b9e911
commit 909e0a4e5c
1 changed files with 6 additions and 3 deletions
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9
mm/vmscan.c
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@@ -248,12 +248,16 @@ 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;
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_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);