[RFC PATCH] mm/damon/core: add short circuit for temporal-goal schemes in damos_adjust_quota()

[Liew Rui Yan]

When using the temporal auto-tuning algorithm, the effective size quota
becomes zero once the goal is [over-]achieved.

In this situation, damos_adjust_quota() still calculates
quota->min_score for it.  However, this min_score will not be used in
this window, because in damon_do_apply_schemes(), damos_quota_is_full()
will always returns true, preventing the scheme from being applied to
any region.

Therefore, add a short circuit for temporal-goal algorithm schemes to
early return from damos_adjust_quota() before calculating min_score.

Signed-off-by: Liew Rui Yan <aethernet65535@xxxxxxxxx>
---

I tested with virtme-ng + perf on a Proactive Memory Reclaim workload;
within measurement noise (~3%), no measurable difference was observed.

The purpose of this patch is to reduce unnecessary operations
(calculating min_score).  But, I'd like to know if this patch needs to
demonstrate that it provides better performance before it's merged.

---
 mm/damon/core.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/mm/damon/core.c b/mm/damon/core.c
index ce8c6f99106e..fdcea989f0e0 100644
--- a/mm/damon/core.c
+++ b/mm/damon/core.c
@@ -3320,6 +3320,8 @@ static void damos_adjust_quota(struct damon_ctx *c, struct damos *s)
 
 	if (!c->ops.get_scheme_score)
 		return;
+	if (quota->esz == 0)
+		return;
 
 	/* Fill up the score histogram */
 	memset(c->regions_score_histogram, 0,
-- 
2.55.0