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 A01D623E334 for ; Wed, 30 Sep 2026 02:34:10 +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=1790735658; cv=none; b=D/0egSh9tza5kaKO5a2Q0yF/4XR5/5MQMIJOz/Sf8vvA/EyW8mmXrz6PBq/rWCwjIqJARCaQ/eqi88/UWhMROvt2zsVDOYQno6sGL+jgEq6wDDkgq597bIY1fgkHfH7/ZNslKOQ4pGyp4PGMQ2pFB79DmWDfVvyZDfxHFxYYOsM= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1790735658; c=relaxed/simple; bh=3xTrTjeMBVPDnAXbwgdZMsY9C6ChZhrBQeC3UZ5d2C4=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=W7jzZvHmYA4t6JDV7e6VZHWH7aFFcOglWKqsY/LmfNeoiAvHEgjq9idPRYUcJ5LRK0XdU51r41TfMR3nkNlwBZ7FfqHtrOKBWjmM+Jv03EP+laXARdhu193zZF5iJukFQM1s294/FxH7Lc09NUifsEsNcc7L7Xcay3OFy8WxL4Q= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=TFl4HFTv; 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="TFl4HFTv" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 2AD001F00899; Wed, 30 Sep 2026 02:34:04 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1790735644; bh=5uc0pW3yq/naLdLk09cygXzXt9AXYUdsgTAkV9FolUo=; h=From:To:Cc:Subject:Date:In-Reply-To:References; b=TFl4HFTvGz/oUBZp/y9fY7c/9PdHRngFhtSw4M/aD09Oj7Rggdw+hEB50X5rUwvdI rqhP2nS6wEiuS1+xELrWxD6Pt8inmr7J4WLrmMAyK8Y4PyPQisKYu8HCJqAwa0QLOt 4D3xPHjb6CcN8ExOhPpVncO4crKVQmXONrpJPhVVSWYNcbKThR2g+vF641skoXjAB6 GViEFb9SLRHU2MwaQ+qZp4I1Gkjie7MKNZfOu+1AkggkmPc/ijPX69Q8HZkG01FZJW H5TzSOHRTp/oI/kcispuMsjqM2tlCxef09iIgzu4uMadFjjasFlr2EPLqFftAiBVKb H7MI/ASdXAjEA== From: Sasha Levin To: stable@vger.kernel.org Cc: Liew Rui Yan , SJ Park , Andrew Morton , Sasha Levin Subject: [PATCH 6.12.y 3/3] mm/damon/core: fix unconditionally skip last region Date: Tue, 29 Sep 2026 22:34:01 -0400 Message-ID: <20260930023401.3420697-3-sashal@kernel.org> X-Mailer: git-send-email 2.53.0 In-Reply-To: <20260930023401.3420697-1-sashal@kernel.org> References: <2026092948-agency-overhand-3fd1@gregkh> <20260930023401.3420697-1-sashal@kernel.org> Precedence: bulk X-Mailing-List: stable@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit From: Liew Rui Yan [ Upstream commit b3723b596b548c837a766aae3553c14a7b15af2b ] 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 Signed-off-by: Sasha Levin --- 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 53d479da2007e..2a24e817e5360 100644 --- a/mm/damon/core.c +++ b/mm/damon/core.c @@ -1325,36 +1325,39 @@ 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, -- 2.53.0