From: Karl Mehltretter The patch in mm-unstable of subject "mm/damon/core: handle uninitialized damos_quota_goal->last_psi_total" scores a PSI quota goal without a previous sample as achieved. This leaves the consist tuner's input unchanged, but the temporal tuner sets its quota to zero for an achieved goal. A running scheme with a nonzero temporal quota therefore loses a charge window after a quota-goal commit. Use the effective quota to preserve the temporal tuner's previous goal-achievement state during an unmeasured round, as SJ suggested [1]. Score the goal as achieved when the effective quota is zero and as not achieved otherwise. A new scheme's initially zero quota stays zero, and the consist tuner's behavior is unchanged. Move the PSI current-value calculation and last_psi_total update into a helper that takes the current PSI total. This lets a unit test cover the unmeasured and measured rounds without depending on system memory pressure. Link: https://lore.kernel.org/damon/20260916001311.101024-1-sj@kernel.org/ [1] Fixes: 2dbb60f789cb ("mm/damon/core: implement PSI metric DAMOS quota goal") Cc: # 6.9.x Cc: Lian Wang Cc: Kunwu Chan Suggested-by: SJ Park Assisted-by: LLM Signed-off-by: Karl Mehltretter Reviewed-by: SJ Park Signed-off-by: SJ Park --- This is a fixup of a patch [1] that is still in mm-unstable tree. [1] https://lore.kernel.org/20260902002725.108635-3-sj@kernel.org Changes from v2 - v2: https://lore.kernel.org/20260921020013.33105-1-kmehltretter@gmail.com - Split out of the series for squashing into the broken patch. - Collect R-b: from SJ. - Update commit message to make clear this is a fixup of a patch in mm-unstable. Changes since v1 - v1: https://lore.kernel.org/20260915060937.3423-1-kmehltretter@gmail.com/ - Use the previous effective quota for the temporal decision, including when it is zero. Keep resetting last_psi_total for new and updated goals. - Move the current-value calculation and last_psi_total update into a helper. Test both tuners with explicit samples and check last_psi_total after each call. mm/damon/core.c | 30 +++++++++++++++++++++++------- 1 file changed, 23 insertions(+), 7 deletions(-) diff --git a/mm/damon/core.c b/mm/damon/core.c index 4687b909d42c..733025b36745 100644 --- a/mm/damon/core.c +++ b/mm/damon/core.c @@ -2956,6 +2956,28 @@ static inline u64 damos_get_some_mem_psi_total(void) #endif /* CONFIG_PSI */ +static void damos_set_psi_current_val(u64 now_psi_total, + struct damos_quota_goal *goal, struct damos *s) +{ + u64 last_psi_total = goal->last_psi_total; + + goal->last_psi_total = now_psi_total; + if (last_psi_total != U64_MAX) { + goal->current_value = now_psi_total - last_psi_total; + return; + } + /* uninitialized last_psi_total; make no effect this round */ + if (s->quota.goal_tuner == DAMOS_QUOTA_GOAL_TUNER_CONSIST) { + goal->current_value = goal->target_value; + return; + } + /* let temporal tuner show the same achievement as in the last round */ + if (!s->quota.esz) + goal->current_value = goal->target_value; + else + goal->current_value = 0; +} + #ifdef CONFIG_NUMA static bool invalid_mem_node(int nid) { @@ -3208,13 +3230,7 @@ static void damos_set_quota_goal_current_value(struct damon_ctx *c, break; case DAMOS_QUOTA_SOME_MEM_PSI_US: now_psi_total = damos_get_some_mem_psi_total(); - /* uninitialized last_psi_total; make no effect this round */ - if (goal->last_psi_total == U64_MAX) - goal->current_value = goal->target_value; - else - goal->current_value = now_psi_total - - goal->last_psi_total; - goal->last_psi_total = now_psi_total; + damos_set_psi_current_val(now_psi_total, goal, s); break; case DAMOS_QUOTA_NODE_MEM_USED_BP: case DAMOS_QUOTA_NODE_MEM_FREE_BP: base-commit: 4b811cf44e3dd87981f18631be832027385f7d4f -- 2.47.3