From a4fe1631f313f75c7dced10d9e7eda816bf0937f Mon Sep 17 00:00:00 2001 From: Johannes Weiner Date: Wed, 3 Jun 2020 16:02:50 -0700 Subject: mm: vmscan: drop unnecessary div0 avoidance rounding in get_scan_count() When we calculate the relative scan pressure between the anon and file LRU lists, we have to assume that reclaim_stat can contain zeroes. To avoid div0 crashes, we add 1 to all denominators like so: anon_prio = swappiness; file_prio = 200 - anon_prio; [...] /* * The amount of pressure on anon vs file pages is inversely * proportional to the fraction of recently scanned pages on * each list that were recently referenced and in active use. */ ap = anon_prio * (reclaim_stat->recent_scanned[0] + 1); ap /= reclaim_stat->recent_rotated[0] + 1; fp = file_prio * (reclaim_stat->recent_scanned[1] + 1); fp /= reclaim_stat->recent_rotated[1] + 1; spin_unlock_irq(&pgdat->lru_lock); fraction[0] = ap; fraction[1] = fp; denominator = ap + fp + 1; While reclaim_stat can contain 0, it's not actually possible for ap + fp to be 0. One of anon_prio or file_prio could be zero, but they must still add up to 200. And the reclaim_stat fraction, due to the +1 in there, is always at least 1. So if one of the two numerators is 0, the other one can't be. ap + fp is always at least 1. Drop the + 1. Signed-off-by: Johannes Weiner Signed-off-by: Andrew Morton Cc: Joonsoo Kim Cc: Michal Hocko Cc: Minchan Kim Cc: Rik van Riel Link: http://lkml.kernel.org/r/20200520232525.798933-8-hannes@cmpxchg.org Signed-off-by: Linus Torvalds --- mm/vmscan.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) (limited to 'mm/vmscan.c') diff --git a/mm/vmscan.c b/mm/vmscan.c index c711efc42cfc..a5a7a8d0764c 100644 --- a/mm/vmscan.c +++ b/mm/vmscan.c @@ -2348,7 +2348,7 @@ static void get_scan_count(struct lruvec *lruvec, struct scan_control *sc, fraction[0] = ap; fraction[1] = fp; - denominator = ap + fp + 1; + denominator = ap + fp; out: for_each_evictable_lru(lru) { int file = is_file_lru(lru); -- cgit v1.2.3