From nobody Sun Sep 27 02:51:50 2026 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-alma10-1.taild15c8.ts.net [100.103.45.18]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 88C3A389DF3; Thu, 27 Aug 2026 04:29:29 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=100.103.45.18 ARC-Seal: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1787804970; cv=none; b=eZhqyRM2KFPt4+exmCtrJ9rmNc0cKFsGiXY7wO4Mj1uqQJHXiSigxV+IZgP3mnGSdKsMOancCTdHuo8y3BUeIkcq1FUTz3q8yMJoLUxY1XNZys8t3xJfzCP++/bqTDgrQvP8zXmq8FzOcPvHFua2H1j/kUyl8yEb67gZ6Ss02ag= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1787804970; c=relaxed/simple; bh=Tc+7cBVCBQnf77YrHoF37bzyflc3XoGdTlEbrJuLgSM=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=SmcQOcU3OaqzcVlwORhzzbePTmEYhGG7zTWVgAoEMDwDZyLNs3U8zwbEALnqyZodVrdhDzSblKZagJ5RlAymcBfaiNpDm4v2O3l4NzzYpHqnWkkmsiRrHhI+IykJTqdwYk9xjQs+EPN1ahfLTPr6PX7ookYr0O2YKKwvt0fXdRk= ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=k2Hocz03; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="k2Hocz03" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 3A8A41F00A3A; Thu, 27 Aug 2026 04:29:29 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1787804969; 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> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="utf-8" 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 =3D damos_get_some_mem_psi_total(); + break; case DAMOS_QUOTA_NODE_MEM_USED_BP: case DAMOS_QUOTA_NODE_MEM_FREE_BP: dst->nid =3D src->nid; @@ -1143,7 +1146,6 @@ static void damos_commit_quota_goal( dst->target_value =3D src->target_value; if (dst->metric =3D=3D DAMOS_QUOTA_USER_INPUT) dst->current_value =3D src->current_value; - /* keep last_psi_total as is, since it will be updated in next cycle */ damos_commit_quota_goal_union(dst, src); } =20 @@ -3741,6 +3743,17 @@ static int kdamond_wait_activation(struct damon_ctx = *ctx) return -EBUSY; } =20 +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 !=3D DAMOS_QUOTA_SOME_MEM_PSI_US) + continue; + goal->last_psi_total =3D damos_get_some_mem_psi_total(); + } +} + static void kdamond_init_ctx(struct damon_ctx *ctx) { unsigned long sample_interval =3D 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); } } =20 --=20 2.47.3 From nobody Sun Sep 27 02:51:50 2026 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-alma10-1.taild15c8.ts.net [100.103.45.18]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id DFA5B38AC78; Thu, 27 Aug 2026 04:29:29 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=100.103.45.18 ARC-Seal: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1787804971; cv=none; b=btwkJ8mYDVqU73gpWQw+GVHfXhMECsHXdeB5isi2wc+06+PMDTp49GMx5TvZxlCMPRrLRiOi4zw6mjzlxWD7M9lPwsyGZMX7EMJ57exbXQNelWNCJUbQyCQ+8xgcMZqYX0SptU9GC5LE91qQBNUNqXGuxacDRmOqh7HwgH/GcBY= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1787804971; c=relaxed/simple; bh=Iv5b61T2zG01D+beUShN6F2FTZvVX8oN+yVJrw+ujzE=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=OK8kZmBMMK8QmaSloM8GOMjjHdpVa1kCKVAngXdEMBgPtDE5txRD1NWKBDYe4/Z402hyiqwGJs1lDU9AC7pcf9J3s5F1yTcpXdwH4VrUBxZiqTQiNa/aF3JdjqmE0r1gb41+LujB0jDiLZkkzB5lTqRSX4m+fY3sujYZHnHOlg4= ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=izYrMHPw; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="izYrMHPw" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 8FF341F00A3E; Thu, 27 Aug 2026 04:29:29 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1787804969; bh=nERbAFEHHSw5ax7MRWud0rpkMohS2ci96UJ8OD+KyJc=; h=From:To:Cc:Subject:Date:In-Reply-To:References; b=izYrMHPwxZ/T5mohTVMD2kb/EMqa5Sw1xgHZkTwTlhGJXkBmsvABfHygDlg84j6ry RueknLBCEZsnFp53JM/LEDbEMLrOb6zFh2FHV64Qer50CtGPcbnjnPAzGRuqKBPBu4 0fij/rL9wBRUJOzRG5fDySXAvMbil4F1h/J1oo5taORYj0Vqb2OrZY1Axz5UiKcCMK 0dLPK/8O3Xia6oTGIISTWtU7e7aXGERZuNtsa9AzZwtciEBXNy6Ntb+fA0g7cjR1OO 3svM2t9PAz+hdYacgQaho2YIQT1+SRnsdveN2DRY5Rk8nGMcXdTbOP45kA+Ow0VsOd EMBggIeJ1YlwQ== From: SJ Park To: Cc: SJ Park , stable@vger.kernel.org, Andrew Morton , Quanmin Yan , damon@lists.linux.dev, linux-kernel@vger.kernel.org, linux-mm@kvack.org Subject: [PATCH 2/2] mm/damon/sysfs: set next refresh jiffies per sysfs context Date: Wed, 26 Aug 2026 21:29:19 -0700 Message-ID: <20260827042920.93580-3-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> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="utf-8" When 'refresh_ms' is set, DAMON sysfs interface periodically updates auto-tuned parameters and DAMOS stats. The timestamp for the next refresh is initialized when a DAMON context starts, and updated in its damon_call() callback function. That is, each DAMON context updates it. However, the timestamp is a global variable that is shared with all the contexts. When there are multiple DAMON contexts having different refresh_ms, the update frequency will be changed, depending on the order of the contexts. When there are multiple kdamonds, it will be even more chaotic. Fix the problem by having the timestamp per each context. The user impact is not very critical. It does not leak, corrupt or crash. The update will not be faster or slower than the lowest and largest refresh_ms values of the contexts, respectively. The user can also manually ask the updates on demand using kdamond state commands. That said, clearly this is a bug. Fixes: 9fd7bb5083d1 ("mm/damon/sysfs: change next_update_jiffies to a globa= l variable") Cc: # 6.18.x Signed-off-by: SJ Park --- mm/damon/sysfs.c | 11 +++++------ 1 file changed, 5 insertions(+), 6 deletions(-) diff --git a/mm/damon/sysfs.c b/mm/damon/sysfs.c index e3858ffab4b22..f05b256c90ee7 100644 --- a/mm/damon/sysfs.c +++ b/mm/damon/sysfs.c @@ -1789,6 +1789,7 @@ struct damon_sysfs_kdamond { struct damon_sysfs_contexts *contexts; struct damon_ctx *damon_ctx; unsigned int refresh_ms; + unsigned long next_refresh_jiffies; }; =20 static struct damon_sysfs_kdamond *damon_sysfs_kdamond_alloc(void) @@ -2215,17 +2216,15 @@ static struct damon_ctx *damon_sysfs_build_ctx( return ctx; } =20 -static unsigned long damon_sysfs_next_update_jiffies; - static int damon_sysfs_repeat_call_fn(void *data) { struct damon_sysfs_kdamond *sysfs_kdamond =3D data; =20 if (!sysfs_kdamond->refresh_ms) return 0; - if (time_before(jiffies, damon_sysfs_next_update_jiffies)) + if (time_before(jiffies, sysfs_kdamond->next_refresh_jiffies)) return 0; - damon_sysfs_next_update_jiffies =3D jiffies + + sysfs_kdamond->next_refresh_jiffies =3D jiffies + msecs_to_jiffies(sysfs_kdamond->refresh_ms); =20 if (!mutex_trylock(&damon_sysfs_lock)) @@ -2273,8 +2272,8 @@ static int damon_sysfs_turn_damon_on(struct damon_sys= fs_kdamond *kdamond) } kdamond->damon_ctx =3D ctx; =20 - damon_sysfs_next_update_jiffies =3D - jiffies + msecs_to_jiffies(kdamond->refresh_ms); + kdamond->next_refresh_jiffies =3D jiffies + + msecs_to_jiffies(kdamond->refresh_ms); =20 repeat_call_control->fn =3D damon_sysfs_repeat_call_fn; repeat_call_control->data =3D kdamond; --=20 2.47.3