On 9/5/24 10:24, SeongJae Park wrote:
damon_feed_loop_next_input() is fragile to overflows. Rewrite code to
avoid overflows. This is not yet well tested on 32bit archs.
Reported-by: Guenter Roeck <linux@xxxxxxxxxxxx>
Closes: https://lore.kernel.org/944f3d5b-9177-48e7-8ec9-7f1331a3fea3@xxxxxxxxxxxx
Fixes: 9294a037c015 ("mm/damon/core: implement goal-oriented feedback-driven quota auto-tuning")
Signed-off-by: SeongJae Park <sj@xxxxxxxxxx>
Passes all my testing except for
Failed unit tests:
arm:mps2-an385:damon_test_ops_registration
arm:mps2-an385:damon
xtensa:de212:damon_test_ops_registration
xtensa:de212:damon
which unrelated and not surprising since those are nommu systems.
Tested-by: Guenter Roeck <linux@xxxxxxxxxxxx>
Thanks,
Guenter
---
As mentioned on the commit message, this is not yet sufficiently tested
on 32bit machines. That's why this is RFC.
mm/damon/core.c | 33 +++++++++++++++++++++++++++------
1 file changed, 27 insertions(+), 6 deletions(-)
diff --git a/mm/damon/core.c b/mm/damon/core.c
index 32677f13f437..1d951c2a1d85 100644
--- a/mm/damon/core.c
+++ b/mm/damon/core.c
@@ -1494,15 +1494,36 @@ static unsigned long damon_feed_loop_next_input(unsigned long last_input,
unsigned long score)
{
const unsigned long goal = 10000;
- unsigned long score_goal_diff = max(goal, score) - min(goal, score);
- unsigned long score_goal_diff_bp = score_goal_diff * 10000 / goal;
- unsigned long compensation = last_input * score_goal_diff_bp / 10000;
/* Set minimum input as 10000 to avoid compensation be zero */
const unsigned long min_input = 10000;
+ unsigned long score_goal_diff;
+ unsigned long compensation;
+
+ if (score == goal)
+ return last_input;
+
+ /* last_input, score <= ULONG_MAX */
+ if (score < goal) {
+ score_goal_diff = goal - score;
+ } else {
+ /* if score_goal_diff > goal, will return min_input anyway */
+ score_goal_diff = min(score - goal, goal);
+ }
+
+ if (last_input < ULONG_MAX / score_goal_diff)
+ compensation = last_input * score_goal_diff / goal;
+ else
+ compensation = last_input / goal * score_goal_diff;
+
+ /* compensation <= last_input <= ULONG_MAX */
+
+ if (goal > score) {
+ if (last_input < ULONG_MAX - compensation)
+ return last_input + compensation;
+ return ULONG_MAX;
+ }
- if (goal > score)
- return last_input + compensation;
- if (last_input > compensation + min_input)
+ if (last_input - compensation > min_input)
return last_input - compensation;
return min_input;
}
