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 C23893BFAD0; Wed, 30 Sep 2026 10:18:57 +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=1790763539; cv=none; b=Q0A03X1lVdCbhG5/YvUk/JDm3UVK0eIFIXXnWZ5xKmhzoE4rFgKJQqyZEgroVlSIVef8hbqQnYtL8fPcXdIz+zqw01njok5Hrp/u54ilX7dEcYXMOiGcOWrsZ5sMtz7M93X+qExCX7L7X9IkmhiniS/BU8RdirfsvngbmGuCPJc= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1790763539; c=relaxed/simple; bh=tj0g8fJaYKaUE2oxkXi40N5hVCetqNIfKT/mFUeLA+0=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=Mw/BWMj2EEYg9ToleMc0cCC08X1sc4KRYiISvNLuSo23xXBWXD8TNOeWczwhurNKkFmbNLZ0teebwryI9PCAqyH+cEQai4QicHyoJ6mKEtfPeveuPEgX93esdIGa3LAjt2Dzl+zBhyxz+BKjhbsqZ/AsYOZ4ia8bb+/wlrhg4ys= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=Fj6J0N0w; 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="Fj6J0N0w" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 0C6E91F000FF; Wed, 30 Sep 2026 10:18:55 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1790763537; bh=aIdp5NFz5jYFmYd/Zp5vP5FJaAUez+gZx8uHmrXspSg=; h=From:To:Cc:Subject:Date:In-Reply-To:References; b=Fj6J0N0wnpX5kI/d7oGj7n8D4HXPboWV2ajKtDICn3tbvOuJKUKauKGOVgsR44nvx 0v74ZsgR0HFXOVOgt9M6nZrUcxtQimZ8/T1t2BFzutkPi0JSCWPK3JmkR2JhHBqODi pJpPZqVQ7uV9ncsf4FBduYSqU8G50Gs9hmY+YEjDr4B/KJse8+SchvTOB4CWzG8k/1 hE04yCnYckI2O0DcpvZioyoWCUgtXvrR0hKB8CBJMjvO9zoXHGlso/3f3DJNdvuyTz s9ihz08ILHdHOswB5tk68CZYT6TCTG0V1aNZLRpzSkz7P9j+PaBC91Qv/NjTdcAlMc qQfvxyY+lVlnQ== From: SJ Park To: stable@vger.kernel.org Cc: Liew Rui Yan , damon@lists.linux.dev, SJ Park , Andrew Morton Subject: [PATCH 6.6.y v2] mm/damon/core: fix unconditionally skip last region Date: Wed, 30 Sep 2026 03:18:52 -0700 Message-ID: <20260930101853.58786-1-sj@kernel.org> X-Mailer: git-send-email 2.47.3 In-Reply-To: <2026092948-moonrise-persecute-3597@gregkh> References: <2026092948-moonrise-persecute-3597@gregkh> Precedence: bulk X-Mailing-List: damon@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit From: Liew Rui Yan Once quota set, the charge_{target,addr}_from unconditionally skips and resets at the last region of the tracked target, so the last region can be skipped even when it has not been processed. Example: 1. Target has 2 regions: R1 (0-100 bytes) and R2 (100-200 bytes). 2. Quota is configured to process only 100 bytes per window. 3. Window 1: Processes R1 (0-100). Quota is full. charge_{target, addr}_from is saved at (Target, 100). 4. Window 2: The loop reaches R2. Because R2 is damon_last_region(t), the old code unconditionally returns true, skipping R2 entirely and resetting the charge_{target,addr}_from. Result: R2 is permanently skipped even though it has never been processed. However, it is important to note that this is a very minor issue. This is because it is triggered only when the previous window saved/kept charge_{target,addr}_from, and in the next window, all regions except the last region were skipped by damos_skip_charged_region(). Fix this by only resetting the charge_{target,addr}_from when last region is reached, only skipping when it is applied or cannot split. Link: https://lore.kernel.org/20260908134739.96919-1-sj@kernel.org Fixes: 50585192bc2e ("mm/damon/schemes: skip already charged targets and regions") Signed-off-by: Liew Rui Yan Reviewed-by: SJ Park Signed-off-by: SJ Park Signed-off-by: Andrew Morton Cc: # v5.16.x (cherry picked from commit b3723b596b548c837a766aae3553c14a7b15af2b) Signed-off-by: SJ Park --- Changes from v1 - v1: https://lore.kernel.org/20260930093707.48739-1-sj@kernel.org - Add missed damon_sz_region(r) <= min_region_sz case change. mm/damon/core.c | 24 ++++++++++++++---------- 1 file changed, 14 insertions(+), 10 deletions(-) diff --git a/mm/damon/core.c b/mm/damon/core.c index 0713fda22682c..c31683c12dd48 100644 --- a/mm/damon/core.c +++ b/mm/damon/core.c @@ -883,37 +883,41 @@ static bool damos_skip_charged_region(struct damon_target *t, struct damon_region *r = *rp; struct damos_quota *quota = &s->quota; unsigned long sz_to_skip; + bool skip = false; /* Skip previously charged regions */ if (quota->charge_target_from) { if (t != quota->charge_target_from) return true; - if (r == damon_last_region(t)) { - quota->charge_target_from = NULL; - quota->charge_addr_from = 0; - return true; - } if (quota->charge_addr_from && - r->ar.end <= quota->charge_addr_from) - return true; + r->ar.end <= quota->charge_addr_from) { + skip = true; + goto out; + } if (quota->charge_addr_from && r->ar.start < quota->charge_addr_from) { sz_to_skip = ALIGN_DOWN(quota->charge_addr_from - r->ar.start, DAMON_MIN_REGION); if (!sz_to_skip) { - if (damon_sz_region(r) <= DAMON_MIN_REGION) - return true; + if (damon_sz_region(r) <= DAMON_MIN_REGION) { + skip = true; + goto out; + } sz_to_skip = DAMON_MIN_REGION; } damon_split_region_at(t, r, sz_to_skip); r = damon_next_region(r); *rp = r; + skip = false; } + } +out: + if (r == damon_last_region(t)) { quota->charge_target_from = NULL; quota->charge_addr_from = 0; } - return false; + return skip; } static void damos_update_stat(struct damos *s, -- 2.47.3