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 EAAC63793A5; Wed, 30 Sep 2026 09:37:25 +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=1790761047; cv=none; b=KWr7OoTIwBQzabH1vQTKCiVVX05mDQK5yEGf7plZPFjpsw4S3SDtgIDJa77lovjXCxkZxunxNN27ca5PesR564ozeSQ6VL7MyNJuqOCdqq0eHMVBDOsiUX+/8T+N30zOBmoEl+WH0QDYkCY6RaEyX6pTl9yCNWzQTz/a8eBF7Ew= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1790761047; c=relaxed/simple; bh=+EkrZEMmFnWOQsnZgC6gn1VpWaNzay67cH2YrkxYNEA=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=KJblWA+CxbQlISTl/BKO9vNXGaipMLqf+QNlx65tkJPpzG27jnnBIwJsZ0nipo7tvuZ1QSgjMw4CBfRVhirjBqc9TgCkj9z0wwewxRse5O20OKU9DrJkfe1T2aC3ZNnELr6ZO2XgYCb03Rbpy/v9gMzw0GuRJ5lYNHop2/i9Kx4= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=gPijUOYF; 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="gPijUOYF" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 4BC7C1F000FF; Wed, 30 Sep 2026 09:37:24 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1790761045; bh=TJhwfM7LT6ym6ruDowV8au+YTRMbhrcGdOAEosWhPaE=; h=From:To:Cc:Subject:Date:In-Reply-To:References; b=gPijUOYFBY30whKuElizvUvyUjYt+04gtiid8sSvsY6VYVxmYt8e/gXTp6fRfCJcp dLuwLlA6PBNCe2OUTyDisXpCEzgvT9bzfnoAcKT1VFIYHEnoPhA7qtTUtg2bUF004z 4c3hr3yfEPump9x1zWbrmuFK4lDqpArWr2vkmyMHsz20AKCsmKKTQ4xng5j3YH+Q/6 fgBcDa8/0rrJdEt9qzQRcoTC6yvTinooUOkOL0IbmGLEUkmNp1CLznSyMugcZUccNm ifL94d2gY8NxjjShq627tQlNd2WWH2Ca7AfPGz+B5hRPFEmH+A0JSiD+qj7gaSZje2 jKA/QHXUfzNew== From: SJ Park To: stable@vger.kernel.org Cc: damon@lists.linux.dev, Liew Rui Yan , SJ Park , Andrew Morton Subject: [PATCH 6.6.y] mm/damon/core: fix unconditionally skip last region Date: Wed, 30 Sep 2026 02:37:07 -0700 Message-ID: <20260930093707.48739-1-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 --- 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 0713fda22682c..5ede1733369f5 100644 --- a/mm/damon/core.c +++ b/mm/damon/core.c @@ -883,19 +883,17 @@ 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) { @@ -909,11 +907,15 @@ 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