On Wed, Feb 28, 2024 at 10:55:00AM +0900, Byungchul Park wrote: > 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; Unfortunately, I don't think that anon = swappiness * file_cost file = (200 - swappiness) * anon_cost is more readable. Sure it's the same, but I think it's clearer to actually see that `anon = total_cost / anon_cost` ratio in the code.
