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 55A9A30DD1B; Wed, 30 Sep 2026 09:28:37 +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=1790760518; cv=none; b=h2AOP2KTqU01I32edSTw01NazVe5GluviARDj4seiOXkizvyBOir/SjZdM9wI1uKvy2xXyrH8aul4i51VX7y9ZPrdKhwxOr3OZgo98tc3L1sDHyjGb7vf85dCp93pD61/hD0OUyaXOP5r1veHEeSgzMM+ojVriGIg/3HiecuL38= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1790760518; c=relaxed/simple; bh=Xh9sEhecDpEPVFZGkk2gnqMsRkUSyI8LZGhckc58uIE=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=tsN9TG6aiCgmrgiq40bx3Oq8gTc0+73qjcKNLtKh4+3qaoS+wylr58yKB5+YxRvJy0PnHTdr/2Xl7v52HyEqqxNHLAV4M1p8TKR4DeCvHvhCu0H5QKFZLJifG8YIyPiQkDWZTs9fjT+6suuXW4+N0WwOLtlZYLkWwz/e9SXcHWY= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=Sqsc8pRz; 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="Sqsc8pRz" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 883221F000FF; Wed, 30 Sep 2026 09:28:35 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1790760516; bh=z3aHHfyyrs0l8iPbF3zXb6TAyOINt0wayQCovhUONWk=; h=From:To:Cc:Subject:Date:In-Reply-To:References; b=Sqsc8pRz+PJaFXnydT83DD1btS1vLMfBvBrfTKZIf5XAP2rbwBSv1Zs8wtEoH2egU E0GYb0LjkD3wggxA4GX9+/pEvOYYyWCjZI2rOB5MQRjeSbhBvFbokTYP09Ylb2Snl7 OfEiAIlaJ0jVuJmPEORYd2x1WVddOJjZ/AGEJRRSJBrntbuDPmreP8V1zNgmCL9h1D XS2g9KqmDninr1CsXi+qHUMF4mkikL7DF/fIifj/tzemoiiLr5tRYs8rvYaj4lb6ym ANiM9BHylcIvJxasMbmOgrQAMEwnEZDtEYaeKm65Xhss4jlRlSpGhUUrpSE2gD/dPn Vf5RQLJtiNBgA== From: SJ Park To: stable@vger.kernel.org Cc: damon@lists.linux.dev, Liew Rui Yan , SJ Park , Andrew Morton Subject: [PATCH 6.12.y] mm/damon/core: fix unconditionally skip last region Date: Wed, 30 Sep 2026 02:28:29 -0700 Message-ID: <20260930092829.45885-1-sj@kernel.org> X-Mailer: git-send-email 2.47.3 In-Reply-To: <2026092948-agency-overhand-3fd1@gregkh> References: <2026092948-agency-overhand-3fd1@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 --- mm/damon/core.c | 18 ++++++++++-------- 1 file changed, 10 insertions(+), 8 deletions(-) diff --git a/mm/damon/core.c b/mm/damon/core.c index 32737cc5f877b..802005d9186e8 100644 --- a/mm/damon/core.c +++ b/mm/damon/core.c @@ -1322,19 +1322,17 @@ 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) { @@ -1348,11 +1346,15 @@ static bool damos_skip_charged_region(struct damon_target *t, 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