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 146AA4D1783; Fri, 9 Oct 2026 13:50:06 +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=1791553809; cv=none; b=e1+hjeSirBdmkynkNRNtEL9tELS6e1q3yKXAsT0anL14UWpIER20fxDn5DZhTLI/EaijMdPpB5AOup37E6kmIuHHFfZsKLmwez2zNaXdzG8Wi+K+tbJbqiGzn9si0CE+yNzQ7LfAaCqrnlpnJVww+bBu7YRXMUA6ZQ5Lq2w/dUU= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1791553809; c=relaxed/simple; bh=D18RrHPud1qI2Cz1IspOwsOX9/qc/GepackvpuKD5XY=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=FCQLqcOVB5nau1YANVSs5XJYYWz542wd9F5QtBMAf5PAZzCns5LAcrbZeJ22GCfw4y456v/OBuDciZBVSXAyaI51qD1ZjeRMUbBqAKp2TfUd/boKzCGw0LAUzWmP/l8stw8ECbrygDmCMIhtAMn0FjgJBmqOGYmxrA4gWAHc8U0= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=POPZCRVT; 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="POPZCRVT" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 4190F1F000FF; Fri, 9 Oct 2026 13:50:05 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1791553806; bh=NGYamTbhyF8fPIDsPezdQjUGd6YDkrBY2lo9+2JMLnM=; h=From:To:Cc:Subject:Date:In-Reply-To:References; b=POPZCRVTopIVD6QueeAp/dbl/2w0eQjppiua1Xgapd3r3bYqxeOThVbyppGzpk+Ua FdxU9T/jq3b0gprHOqC08n2+VSwbkSBFDcXCv/mm8c9ZF9Zaq1use1gra0+sx/neEK 9mZuxnkBuRKpHgwau3IiHViu0chKTSycGzEVW5YYuTfNPfGXSkD5q+YON8/dPfypzD YA7884+MinfTyzde+PG6yLPhO9XUZXFjPbF6uRZiXKo+1j+jGn3CemPeBGvzRjbkJ0 Fno1psmye9lcBTBlPAMduLnRV7SnTFfNAT3v7CMc+eWrQEHmxsHMSOZ8B33jWPfSCl 7ld4as1g2mg4A== From: SJ Park To: stable@vger.kernel.org Cc: damon@lists.linux.dev, Liew Rui Yan , Andrew Morton , SeongJae Park , linux-kernel@vger.kernel.org, linux-mm@kvack.org Subject: [PATCH 6.6.y v3 2/2] mm/damon/core: fix unconditionally skip last region Date: Fri, 9 Oct 2026 06:49:49 -0700 Message-ID: <20261009134949.11507-3-sj@kernel.org> X-Mailer: git-send-email 2.47.3 In-Reply-To: <20261009134949.11507-1-sj@kernel.org> References: <2026092948-moonrise-persecute-3597@gregkh> <20261009134949.11507-1-sj@kernel.org> 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 | 25 ++++++++++++++----------- 1 file changed, 14 insertions(+), 11 deletions(-) diff --git a/mm/damon/core.c b/mm/damon/core.c index c86cac855b9b..c459eae4bbae 100644 --- a/mm/damon/core.c +++ b/mm/damon/core.c @@ -884,36 +884,39 @@ 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, 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); - 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, -- 2.47.3