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Subject[PATCH] mm/vmscan: try to optimize branch procedures.
Date
1. Use unlikely to try to improve branch prediction. The
*total_scan < 0* branch is unlikely to reach, so use unlikely.

2. Optimize *next_deferred >= scanned* condition.
*next_deferred >= scanned* condition could be optimized into
*next_deferred > scanned*, because when *next_deferred == scanned*,
next_deferred shoud be 0, which is covered by the else branch.

3. Merge two branch blocks into one. The *next_deferred > 0* branch
could be merged into *next_deferred > scanned* to simplify the code.

Signed-off-by: Jiang Biao <jiang.biao2@zte.com.cn>
---
mm/vmscan.c | 10 ++++------
1 file changed, 4 insertions(+), 6 deletions(-)

diff --git a/mm/vmscan.c b/mm/vmscan.c
index eb2f031..5f5d4ab 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -338,7 +338,7 @@ static unsigned long do_shrink_slab(struct shrink_control *shrinkctl,
delta *= freeable;
do_div(delta, nr_eligible + 1);
total_scan += delta;
- if (total_scan < 0) {
+ if (unlikely(total_scan < 0)) {
pr_err("shrink_slab: %pF negative objects to delete nr=%ld\n",
shrinker->scan_objects, total_scan);
total_scan = freeable;
@@ -407,18 +407,16 @@ static unsigned long do_shrink_slab(struct shrink_control *shrinkctl,
cond_resched();
}

- if (next_deferred >= scanned)
- next_deferred -= scanned;
- else
- next_deferred = 0;
/*
* move the unused scan count back into the shrinker in a
* manner that handles concurrent updates. If we exhausted the
* scan, there is no need to do an update.
*/
- if (next_deferred > 0)
+ if (next_deferred > scanned) {
+ next_deferred -= scanned;
new_nr = atomic_long_add_return(next_deferred,
&shrinker->nr_deferred[nid]);
+ }
else
new_nr = atomic_long_read(&shrinker->nr_deferred[nid]);

--
2.7.4
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