mm/damon/core: handle zero schemes apply interval

DAMON's logics to determine if this is the time to apply damos schemes
assumes next_apply_sis is always set larger than current
passed_sample_intervals.  And therefore assume continuously incrementing
passed_sample_intervals will make it reaches to the next_apply_sis in
future.  The logic hence does apply the scheme and update next_apply_sis
only if passed_sample_intervals is same to next_apply_sis.

If Schemes apply interval is set as zero, however, next_apply_sis is set
same to current passed_sample_intervals, respectively.  And
passed_sample_intervals is incremented before doing the next_apply_sis
check.  Hence, next_apply_sis becomes larger than next_apply_sis, and the
logic says it is not the time to apply schemes and update next_apply_sis.
In other words, DAMON stops applying schemes until passed_sample_intervals
overflows.

Based on the documents and the common sense, a reasonable behavior for
such inputs would be applying the schemes for every sampling interval.
Handle the case by removing the assumption.

Link: https://lkml.kernel.org/r/20241031183757.49610-3-sj@kernel.org
Fixes: 42f994b71404 ("mm/damon/core: implement scheme-specific apply interval")
Signed-off-by: SeongJae Park <sj@kernel.org>
Cc: <stable@vger.kernel.org>	[6.7.x]
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

diff --git a/mm/damon/core.c b/mm/damon/core.c
index 3131a07569e4eb2f3b4559b1b7221f0d3ef25cab..ce700e694b63666fa8d85e8ad0c4cf892d5c2057 100644 (file)
--- a/mm/damon/core.c
+++ b/mm/damon/core.c
@@ -1412,7 +1412,7 @@ static void damon_do_apply_schemes(struct damon_ctx *c,
        damon_for_each_scheme(s, c) {
                struct damos_quota *quota = &s->quota;
 
-               if (c->passed_sample_intervals != s->next_apply_sis)
+               if (c->passed_sample_intervals < s->next_apply_sis)
                        continue;
 
                if (!s->wmarks.activated)
@@ -1622,7 +1622,7 @@ static void kdamond_apply_schemes(struct damon_ctx *c)
        bool has_schemes_to_apply = false;
 
        damon_for_each_scheme(s, c) {
-               if (c->passed_sample_intervals != s->next_apply_sis)
+               if (c->passed_sample_intervals < s->next_apply_sis)
                        continue;
 
                if (!s->wmarks.activated)
@@ -1642,9 +1642,9 @@ static void kdamond_apply_schemes(struct damon_ctx *c)
        }
 
        damon_for_each_scheme(s, c) {
-               if (c->passed_sample_intervals != s->next_apply_sis)
+               if (c->passed_sample_intervals < s->next_apply_sis)
                        continue;
-               s->next_apply_sis +=
+               s->next_apply_sis = c->passed_sample_intervals +
                        (s->apply_interval_us ? s->apply_interval_us :
                         c->attrs.aggr_interval) / sample_interval;
        }