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a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1788875269; h=from:from:sender:reply-to:subject:subject:date:date: message-id:message-id:to:to:cc:cc:mime-version:mime-version: content-type:content-transfer-encoding:content-transfer-encoding: in-reply-to:references:dkim-signature; bh=A0+1vx5ssYACbosB5yRUtT7K9nBFjhQE+WMx9lniBm8=; b=qvLtoNsOfoImuD4B3mLmoSRn8NxtUw+5WQSD5oUgqdwP4VM5CB1aAkLSNNkDYfdpPZ0uFL qt6V5pdkxC9OPYICqk5gq6GehO7lPDZuf58sexBD6XYSOpDWVc1fIb7mz8Xxulcyp6lN5C Q9lvW8Zg7+mogx4V907sdqfbfNWaDUw= Received: from smtp.kernel.org (quasi.space.kernel.org [100.103.45.18]) by sea.source.kernel.org (Postfix) with ESMTP id 4CE4A4195F; Tue, 8 Sep 2026 13:47:48 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id EF7C51F00A3A; Tue, 8 Sep 2026 13:47:47 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1788875268; bh=A0+1vx5ssYACbosB5yRUtT7K9nBFjhQE+WMx9lniBm8=; h=From:To:Cc:Subject:Date; b=FEm1mdvUsgl8JbaTjjjXn4ngQWgIsDJ3WlnaMSAqxVKqgSnG7Zq2/bhxpaSfntSxh DXisyx9vnI26ygC2pzU0jYMrWh1Y5CAljaY7Fg7FWr7YUC56AmYoL7AqguQluP/0EH Tz6W2kk2AvP2uxMTz1dbgqsgK98Pvb71PEp3id/q/8ix53CNS+oz3BtzMTKVB3PiTv KXi/ecHyHZKN+aBMxAMTMiqqS6Lg2e0tBhY8Oglm9I10opPeGcQaTCxSe8CQhoCVIB XXu8TiHbpx/4rwgdyf2qhb9iLhYSBSUj5MzRXg28dMljsBkKHCY114h17Qx0YMuDfm ZgetKviUSsrtA== From: SJ Park To: Andrew Morton Cc: Liew Rui Yan , stable@vger.kernel.org, SJ Park , damon@lists.linux.dev, linux-kernel@vger.kernel.org, linux-mm@kvack.org Subject: [PATCH v3] mm/damon/core: fix unconditionally skip last region Date: Tue, 8 Sep 2026 06:47:38 -0700 Message-ID: <20260908134739.96919-1-sj@kernel.org> X-Mailer: git-send-email 2.47.3 MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Rspam-User: X-Rspamd-Server: rspam09 X-Rspamd-Queue-Id: 6643C40009 X-Stat-Signature: 4exwcnimfsk59bcjx8c5znm7n653z887 X-HE-Tag: 1788875269-37660 X-HE-Meta: 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 amSKy+16 dF/fCpzzJmcrYpxuJXoP8W6bQym/Pl0o0iEL6ednDIMv4KtGwM57iPYS5ibWKohVcYXVEHvDwU1Rv/WZol+K9u0pN+//7HPWc9RyBvjT+e/ZxIgV1W6AsONIkvZL/gH8Gy5016RyWRfaWCM5O7BVBlwNZDzdG+qh2e8rd0b5L6zq3Hcj3iJbTGKT7tgy9j0/FeV84B5hUh1cP6WVyPf2/747MnuixF7+C9/kVvqPsBPoz1kjUg37VRbOGjtUKHxg8DrNszOybXcyl3VWHVIKB5KRkBGBEwVc4cuaS0GA3wIW2bwn8QpzMpDlJ/A== Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: 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 resets the charge_{target,addr}_from when last region is reached, only skips when it applied or cannot split. Fixes: 50585192bc2e ("mm/damon/schemes: skip already charged targets and regions") Cc: # v5.16.x Cc: Andrew Morton Signed-off-by: Liew Rui Yan Reviewed-by: SJ Park Signed-off-by: SJ Park --- Changes from v2: - v2: https://lore.kernel.org/20260830063159.6347-1-aethernet65535@gmail.com - Collect R-b: from SJ. Changes from v1: - Simplify example in commit message. - Add clarification regarding the severity of the bug to avoid causing users unnecessary afraid. - Modify the patch code, each time the last region is reached, only charge_{target,addr}_from is reset, but the return value depends on the situation. - Modify patch's title from 'mm/damon' to 'mm/damon/core', since it only changes core.c. - v1: https://lore.kernel.org/damon/20260828084737.290024-1-aethernet65535@gmail.com Changes from RFC v1: - Minimal fix, only fixes the issue where the last-region is skipped. - Add an example to the commit message to demonstrate that this error occurs very rarely. - RFC v1: https://lore.kernel.org/damon/20260825124616.5129-1-aethernet65535@gmail.com mm/damon/core.c | 25 ++++++++++++++----------- 1 file changed, 14 insertions(+), 11 deletions(-) diff --git a/mm/damon/core.c b/mm/damon/core.c index a360c41cda89c..7e6cd405161d4 100644 --- a/mm/damon/core.c +++ b/mm/damon/core.c @@ -2452,36 +2452,39 @@ static bool damos_skip_charged_region(struct damon_target *t, { 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, min_region_sz); if (!sz_to_skip) { - if (damon_sz_region(r) <= min_region_sz) - return true; + if (damon_sz_region(r) <= min_region_sz) { + skip = true; + goto out; + } sz_to_skip = min_region_sz; } damon_split_region_at(t, r, sz_to_skip); - return true; + skip = true; } + } +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, base-commit: ab263dd200a7a9101ce3c1374fd23139f29cdac4 -- 2.47.3