[PATCH v4] mm/damon/core: allow esz to be set to zero

[SJ Park <sj@kernel.org>]

From: 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 esz
becomes zero.  However, damos_set_effective_quota() clamps the esz to
min_region_sz when quota->ms is set.

This is a minor issue, the main problem is that it doesn't match the
description in the documentation, which state that if the goal has
already been [over-]achieved, the quota will be set to zero.

Fix this by set quota (esz) as minimum as possible.

Fixes: 8bbde987c2b8 ("mm/damon/core: disallow time-quota setting zero esz")
Cc: <stable@vger.kernel.org> # v7.1.x
Cc: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Liew Rui Yan <aethernet65535@gmail.com>
Reviewed-by: SJ Park <sj@kernel.org>
Signed-off-by: SJ Park <sj@kernel.org>
---
Changes from v3:
- v3: https://lore.kernel.org/20260905124706.3398-1-aethernet65535@gmail.com
- Collect R-b: from SJ.
Changes from v2:
- v2: https://lore.kernel.org/damon/20260902082050.19566-1-aethernet65535@gmail.com                      - Changed implementation, more general implementation provided by SJ. [1]
[1] https://lore.kernel.org/damon/20260902150301.88535-1-sj@kernel.org

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 | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/mm/damon/core.c b/mm/damon/core.c
index 7e6cd405161d4..06cf2ab7e97d7 100644
--- a/mm/damon/core.c
+++ b/mm/damon/core.c
@@ -3242,6 +3242,7 @@ static void damos_set_effective_quota(struct damon_ctx *ctx, struct damos *s)
 	struct damos_quota *quota = &s->quota;
 	unsigned long throughput;
 	unsigned long esz = ULONG_MAX;
+	unsigned long esz_time;
 
 	if (!quota->ms && list_empty(&quota->goals)) {
 		quota->esz = quota->sz;
@@ -3262,8 +3263,8 @@ static void damos_set_effective_quota(struct damon_ctx *ctx, struct damos *s)
 					1000000, quota->total_charged_ns);
 		else
 			throughput = PAGE_SIZE * 1024;
-		esz = min(throughput * quota->ms, esz);
-		esz = max(ctx->min_region_sz, esz);
+		esz_time = max(throughput * quota->ms, ctx->min_region_sz);
+		esz = min(esz_time, esz);
 	}
 
 	if (quota->sz && quota->sz < esz)

base-commit: 6f8c7324e336e626bd993bc36f177dcf493a871f
-- 
2.47.3