From mboxrd@z Thu Jan 1 00:00:00 1970 Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.remote-ip=100.103.45.18 ARC-Seal: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; cv=none; t=1794590906; b=Orh3fcy5OIVcaTfafesJ1Y08pjtsYWeKXHWqAZZCfA41GOpC4fWHHLhTf6zJd4+BNkDE 9rqxKpALneQD/OO0ziKHOMvc4dG2hn1lLnhGXq5E6vN7TPHSeR0aRsmyMtKbQoNJsWuaT h20e2LHmyrdOWBNXogjWBSqO0J4+so3V+/A8UI+0b2JU4+ZR3/54jrn3ciyl3/NtrHKQV L9xBz7iZDsOTDuBOCb3o5NOFZybXkjFI4expWo40GxxnsnILBtPRva4PEGr0EB8T4mmub 5J3x8YqOe7oKuzQrCGbqwPHUDwn6D0a1tehU25qnW/2Q2Aq+iZscm0LcVDQ1ldnsAFQ== ARC-Message-Signature: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; c=relaxed/relaxed; t=1794590906; h=Received:DKIM-Signature:From:To:Cc:Subject:Date:Message-ID:X-Mailer: In-Reply-To:References:User-Agent:X-stable:X-Patchwork-Hint: MIME-Version:Content-Transfer-Encoding; bh=TV/asRgHA8uzH+InN/CvWuTF7QMBJwzXnGD+M8mKX48=; b=BNcuPkTkdTqboGik+BDX85xwiVu0tEaLLWxTgYzi/ItY/maaIulnd8s0/BGrT9dLQMmO 5mlalRvo0jbaH8t/82sS6Fp1Kd2C7RfxYw6iNEtHgBJgFa3+5m2qPR77hctqNcsRynOdh Lx72018XH+dRAwhAHxqlZhew/LmBkj/A9kC/B37nJiMN53oh9x1PNyYNJhgtF+PIZEiMi B7Ig07t1toVy2JiC8DllIJ59hk4cdA/7F5+q7TA5Ob0DhnFI+K3oq+cvzvN/rcwYpVzzk 1bnw5WRKcLGe2WSHovXm5upYWeAZRl6ZL5DGEaX3NxSKidNzE/fk00L7a/1Rgndl4bQ== ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dkim=pass header.d=linuxfoundation.org header.i=@linuxfoundation.org header.a=rsa-sha256 header.s=korg header.b=1oOsCvdO; arc=none smtp.remote-ip=100.103.45.18 Received: from smtp.kernel.org (quasi.space.kernel.org [100.103.45.18]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature ECDSA (prime256v1)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 1D077606E237; Fri, 13 Nov 2026 17:28:26 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.a=rsa-sha256 header.s=korg header.b=1oOsCvdO Received: by smtp.kernel.org (Postfix) with ESMTPSA id C384E1F000C4; Fri, 13 Nov 2026 17:28:25 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linuxfoundation.org; s=korg; t=1794590906; bh=TV/asRgHA8uzH+InN/CvWuTF7QMBJwzXnGD+M8mKX48=; h=From:To:Cc:Subject:Date:In-Reply-To:References; b=1oOsCvdOq7TArZGMvn5dIsEkLIe39TM3HhUwLyyPSB4n0vTdOwp1e1oPFmL+Uwnar OGtRtmW11lB2GJCaHTbEqmFcEMs3pwTPCSpmn9Q7EHZsP8NQvB21B17mzVokS36CG3 zQI7RIyAMh7eSYN3VJwJoE08ZuVZsNEOpiPhrKkQ= From: Greg Kroah-Hartman To: stable@vger.kernel.org Cc: Greg Kroah-Hartman , patches@lists.linux.dev, SJ Park , Andrew Morton , Lian Wang , Kunwu Chan , Brendan Higgins , David Gow , Quanmin Yan , Sasha Levin Subject: [PATCH 6.12 094/670] mm/damon/core: handle uninitialized damos_quota_goal->last_psi_total Date: Fri, 13 Nov 2026 10:44:18 -0500 Message-ID: <20261113153815.086316727@linuxfoundation.org> X-Mailer: git-send-email 2.56.0 In-Reply-To: <20261113153811.177190860@linuxfoundation.org> References: <20261113153811.177190860@linuxfoundation.org> User-Agent: quilt/0.69 X-stable: review X-Patchwork-Hint: ignore X-Mailing-List: patches@lists.linux.dev List-Id: List-Post: List-Help: List-Subscribe: List-Unsubscribe: List-Owner: Precedence: list MIME-Version: 1.0 Content-Transfer-Encoding: 8bit 6.12-stable review patch. If anyone has any objections, please let me know. ------------------ From: SJ Park [ Upstream commit 29c6084658af41b5b1fefd873d26d441830ced34 ] 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. Check last_psi_total initialization and skip the tuning round when it is not initialized. For this, initialize last_psi_total with U64_MAX in the goal creation and the goal commit time. U64_MAX means the field is not initialized. The tuning round shows the value and adjusts it to guarantee the current quota is maintained for the round, and last_psi_total is correctly initialized on the next round. Before this change, committing a new PSI goal on an existing PSI goal with goal-only DAMON sysfs command (commit_schemes_quota_goals) just worked. After this change, the tuning round right after the commit will be unnecessarily skipped, because last_psi_total is unconditionally marked as not initialized in the damos_commit_quota_goal_union(). This is an intended tradeoff for simplicity. Skipping just one round of tuning is no problem. Meanwhile it makes both the code and the behavior simple to understand. Also update the quota goal commit unit test for changed last_psi_total setup behavior. The issue was discovered [1] by Sashiko. Link: https://lore.kernel.org/20260902002725.108635-3-sj@kernel.org Link: https://lore.kernel.org/20260718005316.89585-1-sj@kernel.org [1] Fixes: 2dbb60f789cb ("mm/damon/core: implement PSI metric DAMOS quota goal") Signed-off-by: SJ Park Signed-off-by: Andrew Morton Reviewed-by: Lian Wang Tested-by: Lian Wang Reviewed-by: Kunwu Chan Cc: Brendan Higgins Cc: David Gow Cc: Quanmin Yan Cc: # 6.9.x Signed-off-by: SJ Park Signed-off-by: Sasha Levin --- mm/damon/core.c | 12 ++++++++++-- 1 file changed, 10 insertions(+), 2 deletions(-) diff --git a/mm/damon/core.c b/mm/damon/core.c index fc4f9aa0a3620..4952ca7ac00dc 100644 --- a/mm/damon/core.c +++ b/mm/damon/core.c @@ -324,6 +324,8 @@ struct damos_quota_goal *damos_new_quota_goal( return NULL; goal->metric = metric; goal->target_value = target_value; + if (metric == DAMOS_QUOTA_SOME_MEM_PSI_US) + goal->last_psi_total = U64_MAX; INIT_LIST_HEAD(&goal->list); return goal; } @@ -707,7 +709,8 @@ static int 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 */ + else if (dst->metric == DAMOS_QUOTA_SOME_MEM_PSI_US) + dst->last_psi_total = U64_MAX; return 0; } @@ -1622,7 +1625,12 @@ static void damos_set_quota_goal_current_value(struct damos_quota_goal *goal) break; case DAMOS_QUOTA_SOME_MEM_PSI_US: now_psi_total = damos_get_some_mem_psi_total(); - goal->current_value = now_psi_total - goal->last_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; break; default: -- 2.53.0