The current way to calculate fractions for SACN_FRACT is little readable
and more complicated than it should be. It also performs unnecessary
division and adjustment to avoid zero operands. Prune away by
multiplying the fractions by 'anon_cost * file_cost / (3 * total_cost)':
where:
total_cost = sc->anon_cost + sc->file_cost
anon_cost = total_cost + sc->anon_cost
file_cost = total_cost + sc->file_cost
before:
fraction[0] = swappiness * 3 * total_cost / anon_cost
fraction[1] = (200 - swappiness) * 3 * total_cost / file_cost
after:
fraction[0] = swappiness * file_cost
fraction[1] = (200 - swappiness) * anon_cost
Worth noting that this patch doesn't change the formula.
Signed-off-by: Byungchul Park <byungchul@xxxxxx>
---
mm/vmscan.c | 14 +++-----------
1 file changed, 3 insertions(+), 11 deletions(-)
diff --git a/mm/vmscan.c b/mm/vmscan.c
index 4657440854db..7b33fcc1cbdc 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -2339,7 +2339,6 @@ static void get_scan_count(struct lruvec *lruvec, struct scan_control *sc,
u64 fraction[ANON_AND_FILE];
u64 denominator = 0; /* gcc */
enum scan_balance scan_balance;
- unsigned long ap, fp;
enum lru_list lru;
/*
@@ -2416,17 +2415,10 @@ static void get_scan_count(struct lruvec *lruvec, struct scan_control *sc,
total_cost = sc->anon_cost + sc->file_cost;
anon_cost = total_cost + sc->anon_cost;
file_cost = total_cost + sc->file_cost;
- total_cost = anon_cost + file_cost;
- ap = swappiness * (total_cost + 1);
- ap /= anon_cost + 1;
-
- fp = (200 - swappiness) * (total_cost + 1);
- fp /= file_cost + 1;
-
- fraction[0] = ap;
- fraction[1] = fp;
- denominator = ap + fp;
+ fraction[0] = swappiness * file_cost;
+ fraction[1] = (200 - swappiness) * anon_cost;
+ denominator = fraction[0] + fraction[1];
out:
for_each_evictable_lru(lru) {
int file = is_file_lru(lru);
--
2.17.1
