[PATCH v2] mm/damon/core: allow esz to be set to zero

[Liew Rui Yan <aethernet65535@gmail.com>]

When the temporal quota goal tuner determines that the goal has been
achieved (score >= 10000), it sets esz_bp to zero so that the effective
quota (esz) becomes zero.  However, damos_set_effective_quota() clamps
the quota to min_region_sz, preventing the quota from ever reaching
zero.

Fix this by adding a check for zero esz_bp.

Fixes: 8bbde987c2b8 ("mm/damon/core: disallow time-quota setting zero esz")
Cc: <stable@vger.kernel.org> # v7.1.x
Signed-off-by: Liew Rui Yan <aethernet65535@gmail.com>
---

Changes from v1:
- v1: https://lore.kernel.org/damon/20260901105951.106246-1-aethernet65535@gmail.com
- Changed implementation.  The initial solution skipped the
  min_region_sz clamping when esz was already zero.  However, this would
  revert the fix from commit 8bbde987c2b8 and cause a regression.  This
  revision fixes the issue by adding a specific check for a zero esz_bp.
- Changed patch title, original title: fix quota could not be set to
  zero

---
 mm/damon/core.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/mm/damon/core.c b/mm/damon/core.c
index e13a154aa4b9..8e3ded1a2cf6 100644
--- a/mm/damon/core.c
+++ b/mm/damon/core.c
@@ -3133,6 +3133,9 @@ static void damos_set_effective_quota(struct damon_ctx *ctx, struct damos *s)
 	if (quota->sz && quota->sz < esz)
 		esz = quota->sz;
 
+	if (!quota->esz_bp)
+		esz = 0;
+
 	quota->esz = esz;
 }
 
-- 
2.55.0