[RFC PATCH 3/5] mm/damon/core: floor effective quota size at minimum region size

[Ravi Jonnalagadda]

The CONSIST quota goal tuner initializes esz_bp to 0, producing an
effective quota size (esz) of 1 byte on the first tick.
damos_quota_is_full() rejects all regions when esz < min_region_sz
(default PAGE_SIZE = 4096), so no regions can be tried and no
feedback reaches the tuner — a bootstrapping deadlock.

Floor esz at ctx->min_region_sz after the tuner computes it, guarded
by an esz != 0 check.  The guard preserves the temporal tuner's
intentional stop behavior: when score >= 10000 (goal met), temporal
sets esz_bp = 0 to halt migration; the floor must not override that.

Signed-off-by: Ravi Jonnalagadda <ravis.opensrc@xxxxxxxxx>
---
 mm/damon/core.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/mm/damon/core.c b/mm/damon/core.c
index fd1db234ca304..d33c4360cbd60 100644
--- a/mm/damon/core.c
+++ b/mm/damon/core.c
@@ -2650,6 +2650,10 @@ static void damos_set_effective_quota(struct damon_ctx *ctx, struct damos *s)
 		esz = quota->esz_bp / 10000;
 	}
 
+	/* avoid cold-start deadlock, but respect tuner stop signal (esz=0) */
+	if (esz)
+		esz = max_t(unsigned long, esz, ctx->min_region_sz);
+
 	if (quota->ms) {
 		if (quota->total_charged_ns)
 			throughput = mult_frac(quota->total_charged_sz,
-- 
2.43.0