[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]
Message-ID: <df091a2c-b9cc-46ce-9107-b3300cf06abc@roeck-us.net>
Date: Thu, 5 Sep 2024 14:40:45 -0700
From: Guenter Roeck <linux@...ck-us.net>
To: SeongJae Park <sj@...nel.org>
Cc: damon@...ts.linux.dev, linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: Re: [RFC PATCH] mm/damon/core: avoid overflow in
damon_feed_loop_next_input()
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@...ck-us.net>
> Closes: https://lore.kernel.org/944f3d5b-9177-48e7-8ec9-7f1331a3fea3@roeck-us.net
> Fixes: 9294a037c015 ("mm/damon/core: implement goal-oriented feedback-driven quota auto-tuning")
> Signed-off-by: SeongJae Park <sj@...nel.org>
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@...ck-us.net>
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;
> }
Powered by blists - more mailing lists