From mboxrd@z Thu Jan 1 00:00:00 1970 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 305143128B8; Sat, 3 Oct 2026 15:48:25 +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=1791042508; cv=none; b=DzgFXombvAG3OVkg4pyWWHckc276GRxaLOaS7MLSuNe40S9DOHH3AjQFmGp9sxT/tnoar/rqhRBGKJ9iAQYgbWnAABfSGMRr08dV7mFAOo0ZjyhK7NMo65earcJ0OWVrq8+JCbYSIm4mdrx5W51B9KdlvALedG80d8Y1d2Rzj/8= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1791042508; c=relaxed/simple; bh=iSEehLHW+LcjYLM0ZXcO0oMMmdB6yw335xhofLx/GhE=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=GaVRFrqTQ8YWT92v+Iq2kuhOTtZbDLDXmxaRu07si1Tt4dfV2GgqnaDdsi0w+GL9soa2LT4NtkSsgBUbzqRhnkIrgrnBJTTW6sprwWQZ/XbPC/POEROsTdOcCEvJDgLIMRmEKKOyCjsGDdKD76Njx5EnkJcpHACkO+WphhcQWHY= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=mDDgH2kn; 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="mDDgH2kn" Received: by smtp.kernel.org (Postfix) with ESMTPSA id A338F1F0089B; Sat, 3 Oct 2026 15:48:23 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1791042505; bh=91Iq4Hbdda1nW+Qrueu6btrgVUjeTlDMkRIdyYJbrlk=; h=From:To:Cc:Subject:Date:In-Reply-To:References; b=mDDgH2knrpdl7NXzz9Py4XBKW+ZBSjxMAvGcHe+KQlpqH5cax1/JsEOlSdQCyGdwu fK4RPWA8Re6JhexHPCRoIY8S3CZKJvvG8H3pH4esFn/9jNsYTRqHvKyXTQ2jZ78baB 2L4iNh6F4TikeP/MhBvtU5IPzKVtWPUZ27Rq2Vz0MbGdOfRO/FzQSzNGgiguF5Pgmr cHLx+KKiaJMKA7bK+soSrf3OjnjsoJdAcjtCJqxspKEzup7o6og49HSppX75VO721j s8B+JRashW43Fcmo7tJnDrLLLhFJ6XYW/jsSBbLp9dGz7Y3pu4tfEbzlyQj7RsS9RP UFOGP0OJWSoeA== From: SJ Park To: stable@vger.kernel.org Cc: damon@lists.linux.dev, SJ Park , Andrew Morton , Kunwu Chan Subject: [PATCH 6.6.y] mm/damon/core: don't skip damos_adjust_quota() while esz is not zero Date: Sat, 3 Oct 2026 08:48:18 -0700 Message-ID: <20261003154818.24786-1-sj@kernel.org> X-Mailer: git-send-email 2.47.3 In-Reply-To: <2026100318-preteen-hazelnut-d38b@gregkh> References: <2026100318-preteen-hazelnut-d38b@gregkh> Precedence: bulk X-Mailing-List: damon@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit DAMOS could unexpectedly stop working when a user disables quota using the online parameters commit feature. Fix it by correcting a wrong quota unset check in damos_adjust_quota(). DAMON users could disable all quotas by unsetting time and size quotas, and removing all quota goals. The intention of disabling quotas would be making DAMOS run at full speed. When such quota disabled setup is detected, damos_adjust_quota() skips all its work. The skipped works include effective size quota (damos_quota->esz) updates and charged quota amount (damos_quota->charged_sz) resets. The intention is to avoid doing unnecessary work when quotas are disabled. However, users could do the setup while effective size quota is non-zero, by doing the disabling with the online DAMON parameters commit feature. In this case, because the effective size quota exists, DAMOS will keep working with the quota until it is fully charged. After the effective quota is fully charged, the charged quota amount (damos_quota->charged_sz) cannot be reset because damos_adjust_quota() skips it. Then, DAMOS stops working until the quota is newly set or DAMON is entirely restarted. The problem happens because damos_adjust_quota() assumes the user setup for disabling quota immediately disabled it. In reality, the quota is still working until the effective size quota is also updated to zero. Other logic for catching that uses damos_quota_is_set(), which understands the fact and therefore checks the effective size quota in addition to the user setup. Fix the issue by using damos_quota_is_set() in damos_adjust_quota() to determine if its works should be skipped. The user impact is a non-deterministic and unexpected DAMOS stop behavior. That is, users would disable quotas using the online parameters commit feature, expecting DAMOS will run at full speed. However, depending on the timing, the setup can be updated while the effective size quota is non-zero. Due to the above mentioned internal mechanism, DAMOS stops working instead of running at full speed. It is unexpected behavior. It is also non-deterministic because sometimes the setup is done when the effective size quota is zero, depending on the timing. It doesn't cause critical issues like crashes or leaks. Users can simply set a reasonable quota again, or restart DAMON. But definitely it is an unexpected and non-deterministic behavior that makes it difficult to reliably use. Also investigating the root cause of the behavior would be quite difficult. Link: https://lore.kernel.org/20260916135020.86483-1-sj@kernel.org Fixes: da87878010e5 ("mm/damon/sysfs: support online inputs update") Signed-off-by: SJ Park Signed-off-by: Andrew Morton Reviewed-by: Kunwu Chan Cc: # 5.19.x Signed-off-by: SJ Park --- mm/damon/core.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/mm/damon/core.c b/mm/damon/core.c index fe91b296f4c6..bd46a63b611c 100644 --- a/mm/damon/core.c +++ b/mm/damon/core.c @@ -1087,7 +1087,7 @@ static void damos_adjust_quota(struct damon_ctx *c, struct damos *s) unsigned long cumulated_sz; unsigned int score, max_score = 0; - if (!quota->ms && !quota->sz) + if (!quota->esz && !quota->ms && !quota->sz) return; /* First charge window */ -- 2.47.3