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bh=8OhKNZlcbIRJFXZB0BB5LWgKdrRUKnRyLDo/v7ocG2I=; h=From:To:Cc:Subject:Date:In-Reply-To:References; b=k2Hocz03j8gNlThKs7aOx21XiilaMgxNp5HiTEagJ2jw0S1YA31Qu0dnzA5e0wM0Q 6cszBKjC5flBpySgaW+OX/GVYik/CWO8K7n3x9JfiEVVKsWyay0PmeR9Ry8aS2qWtM j6pvS/EwqMjgPkBxa3FxCMRSLaFWwARxLtHQnB19qRnHimv9mEk2cNlDELapYEG912 sxuP8M6I+tcwvP9q+nJ5plp+Ha/WRDSNCvW2z8ibZIV8noyp+3TnObKsGwb9CsX/zo LDj0+Bl2L4yAgBH7isgbQPx6so87RibHJywVlLPHJyXc9F+1e8fiPLTI2e+6Hm/8rO 40mx2wW3AKMog== From: SJ Park To: Cc: SJ Park , stable@vger.kernel.org, Andrew Morton , damon@lists.linux.dev, linux-kernel@vger.kernel.org, linux-mm@kvack.org Subject: [PATCH 1/2] mm/damon/core: initialize damos_quota_goal->last_psi_total Date: Wed, 26 Aug 2026 21:29:18 -0700 Message-ID: <20260827042920.93580-2-sj@kernel.org> X-Mailer: git-send-email 2.47.3 In-Reply-To: <20260827042920.93580-1-sj@kernel.org> References: <20260827042920.93580-1-sj@kernel.org> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Rspam-User: X-Stat-Signature: 4drqafk8dxe8z6unxbwhps7b5azntbum X-Rspamd-Queue-Id: 20F6980003 X-Rspamd-Server: rspam06 X-HE-Tag: 1787804969-481254 X-HE-Meta: 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 8kOktZjl WyVuFQiJ8gHM17dPe7WYuKX5tZ5eyJ1/nMcXxGuhPISfpzroDoX1cajDBDgiKAtYNNLRh9/Xu1cezSdzMkX74ML2V9SvMC3JuhnVMqgpdsfMOGRajrZPsnTPRdHqcgebNRUjyqYwsbLdq/IjrJ4jY2CEfPjOFgMzyJKoS3CPyWrZDv0d9jo+5Ps2FLIxnLwbu+RZ/fhh/jsniHhKldpfKP7CZgSLBHAFPoZyhf6OBUM0Iw3aE2WXrZOCnMZdLh5IVpLrq2zkLrxrESnCVz1rsl5T75Q== Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: When DAMOS_QUOTA_SOME_MEM_PSI_US metric damos quota goal is set, the PSI delta for the feedback loop is calculated using damos_quota_goal->last_psi_total. However, it is initialized only after the first feedback loop. The first iteration of the loop uses the uninitialized value. As a result, the feedback loop can change the effective quota in an unexpected way at the first iteration. The user impact of the issue is not big, because the issue impacts only the first iteration of the feedback loop. The feedback loop also has an internal cap of the quota adjustment. The wrong adjustment will soon be corrected over a few iterations. For this reason, doing no initialization at commit time was intentional. It is also explicitly commented. That said, nobody likes behaviors that are unexpected or difficult to be expected. Fixing it is also simple and not expensive. Initialize the field at the beginning of kdamond and each commit of SOME_MEM_PSI_US type quota goals. The issue was discovered [1] by Sashiko. [1] https://lore.kernel.org/20260718005316.89585-1-sj@kernel.org Fixes: 2dbb60f789cb ("mm/damon/core: implement PSI metric DAMOS quota goal") Cc: # 6.9.x Signed-off-by: SJ Park --- mm/damon/core.c | 16 +++++++++++++++- 1 file changed, 15 insertions(+), 1 deletion(-) diff --git a/mm/damon/core.c b/mm/damon/core.c index f8dddbff74a77..0d4a571482fb9 100644 --- a/mm/damon/core.c +++ b/mm/damon/core.c @@ -1122,6 +1122,9 @@ static void damos_commit_quota_goal_union( struct damos_quota_goal *dst, struct damos_quota_goal *src) { switch (dst->metric) { + case DAMOS_QUOTA_SOME_MEM_PSI_US: + dst->last_psi_total = damos_get_some_mem_psi_total(); + break; case DAMOS_QUOTA_NODE_MEM_USED_BP: case DAMOS_QUOTA_NODE_MEM_FREE_BP: dst->nid = src->nid; @@ -1143,7 +1146,6 @@ static void damos_commit_quota_goal( dst->target_value = src->target_value; if (dst->metric == DAMOS_QUOTA_USER_INPUT) dst->current_value = src->current_value; - /* keep last_psi_total as is, since it will be updated in next cycle */ damos_commit_quota_goal_union(dst, src); } @@ -3741,6 +3743,17 @@ static int kdamond_wait_activation(struct damon_ctx *ctx) return -EBUSY; } +static void damos_init_quota_goal_last_psi(struct damos *s) +{ + struct damos_quota_goal *goal; + + damos_for_each_quota_goal(goal, &s->quota) { + if (goal->metric != DAMOS_QUOTA_SOME_MEM_PSI_US) + continue; + goal->last_psi_total = damos_get_some_mem_psi_total(); + } +} + static void kdamond_init_ctx(struct damon_ctx *ctx) { unsigned long sample_interval = ctx->attrs.sample_interval ? @@ -3757,6 +3770,7 @@ static void kdamond_init_ctx(struct damon_ctx *ctx) damon_for_each_scheme(scheme, ctx) { damos_set_next_apply_sis(scheme, ctx); damos_set_filters_default_reject(scheme); + damos_init_quota_goal_last_psi(scheme); } } -- 2.47.3