Hi Jonghyeon,
On Wed, 30 Mar 2022 19:53:02 +0900 Jonghyeon Kim <tome01@xxxxxxxxxx> wrote:
> In the DAMON, the minimum wait time of the schemes decides whether the
> kernel wakes up 'kdamon_fn()'. But since the minimum wait time is
> initialized to zero, there are corner cases against the original objective.
>
> For example, if we have several schemes for one target, and if the wait
> time of the first scheme is zero, the minimum wait time will set zero,
> which means 'kdamond_fn()' should wake up to apply this scheme. However,
> in the following scheme, wait time can be set to non-zero. Thus, the
> mininum wait time will be set to non-zero, which can cause sleeping this
> interval for 'kdamon_fn()' due to one deactivated last scheme.
Good catch, thanks!
>
> This commit prevents making DAMON monitoring inactive state due to other
> deactivated schemes.
>
> Signed-off-by: Jonghyeon Kim <tome01@xxxxxxxxxx>
Reviewed-by: SeongJae Park <sj@xxxxxxxxxx>
Thanks,
SJ
> ---
> mm/damon/core.c | 5 ++++-
> 1 file changed, 4 insertions(+), 1 deletion(-)
>
> diff --git a/mm/damon/core.c b/mm/damon/core.c
> index c1e0fed4e877..5ce8d7c867f0 100644
> --- a/mm/damon/core.c
> +++ b/mm/damon/core.c
> @@ -1019,12 +1019,15 @@ static int kdamond_wait_activation(struct damon_ctx *ctx)
> struct damos *s;
> unsigned long wait_time;
> unsigned long min_wait_time = 0;
> + bool init_wait_time = false;
>
> while (!kdamond_need_stop(ctx)) {
> damon_for_each_scheme(s, ctx) {
> wait_time = damos_wmark_wait_us(s);
> - if (!min_wait_time || wait_time < min_wait_time)
> + if (!init_wait_time || wait_time < min_wait_time) {
> + init_wait_time = true;
> min_wait_time = wait_time;
> + }
> }
> if (!min_wait_time)
> return 0;
> --
> 2.17.1
>
