From mboxrd@z Thu Jan 1 00:00:00 1970 Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.remote-ip=100.103.45.18 ARC-Seal: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; cv=none; t=1794272539; b=UenVcQKuXtyUEg0oVTmCtRyoqKdcKxQT9ziWysdwT7VCmkggqyc/ftZrOxChDPtHpgV7 55n0125fNDJ4/xlBzzNEwQa0msFjul12xisxeQ/udU7ZanXSbxO4sKzuufr92hyetiL2K Yq7Cu5oThoMS5IKG1EzQRSy8+wfgcFmyBSvI+GUqqRQE9uNOMxra2upxK9ik7lsm+1cCd J4VSKAnQjj//QtWbeTQAP9e2/h1Lxd1hQNAaJ0HjigbIBPzoyf+Brb45gAcAVrLGh7sYT bXt8wScXTHnuAW+f7LSgDPt0YbSqsIILq8HTRx5edcVIHy8eZrWvQmT3hzmQM+MizCg== ARC-Message-Signature: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; c=relaxed/relaxed; t=1794272539; h=Received:DKIM-Signature:Date:To:From:Subject:Message-Id; bh=20hEICLil4kCUjTHTP5j0xVG6xrZnV5pk0kULcwM08M=; b=LlIWOuGBO2+PgnXuqaVGaZPx/LCPZgne5wA6xTJ3Tus6NeAqeGvD+KBwsIWsnZnkflzk Qfgvoc6waAg2vdDMVjoslEAEO2x7E6rVOJny1Yyq3YROh93khNqAtY7oJ6bRtWUCbelkZ F5ofbjlWGJlvjSzlvrXlv2P5P9OgcN8EcxsRXK7WgwB5tm4A81Fwz6g/VcetZ7PtvN1bS FDg+nS9Xfyjsmmh2r40h7uZ45JE2TWPMti2agTHR2CYMnE9OOt61hXFbzkq9IBuQqofkp YuMeMCIK/16ydLbbEhRkLzcOhCP3vZTkCmVI9Tuz81/1wyZUg5v0+qbySKpF7PPgCEA== ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dkim=pass header.d=linux-foundation.org header.i=@linux-foundation.org header.a=rsa-sha256 header.s=korg header.b=M53apsbw; arc=none smtp.remote-ip=100.103.45.18 Received: from smtp.kernel.org (quasi.space.kernel.org [100.103.45.18]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature ECDSA (prime256v1)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 84654606A32A; Tue, 10 Nov 2026 01:02:19 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linux-foundation.org header.i=@linux-foundation.org header.a=rsa-sha256 header.s=korg header.b=M53apsbw Received: by smtp.kernel.org (Postfix) with ESMTPSA id 1D8AE1F0089F; Tue, 10 Nov 2026 01:02:19 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux-foundation.org; s=korg; t=1794272539; bh=20hEICLil4kCUjTHTP5j0xVG6xrZnV5pk0kULcwM08M=; h=Date:To:From:Subject; b=M53apsbwRQ1KxcaxC6OLKxtLt+9QCDxH2uz0DmtHag8ss9TSm7Y+nUUlaw8dG8gKU KCeYRih8r9QDDeOQIqaTfVjGV1oCEBCvJ8quRadGACIuFJP+8fI4iO9T1QwocIxBPD FZkbulQQT0kss14K1KUeeTRBNfx/wNphLUOCuMXk= Date: Mon, 09 Nov 2026 17:02:18 -0800 To: mm-commits@vger.kernel.org,stable@vger.kernel.org,sj@kernel.org, gkwang@linx-info.com,akpm@linux-foundation.org From: Andrew Morton Subject: + mm-damon-stat-avoid-overflow-in-estimated_memory_bandwidth-calculation.patch added to mm-hotfixes-unstable branch Message-Id: <20261110010219.1D8AE1F0089F@smtp.kernel.org> X-Mailing-List: stable@vger.kernel.org List-Id: List-Post: List-Help: List-Subscribe: List-Unsubscribe: List-Owner: Precedence: list The patch titled Subject: mm/damon/stat: avoid overflow in estimated_memory_bandwidth calculation has been added to the -mm mm-hotfixes-unstable branch. Its filename is mm-damon-stat-avoid-overflow-in-estimated_memory_bandwidth-calculation.patch This patch will shortly appear at https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/mm-damon-stat-avoid-overflow-in-estimated_memory_bandwidth-calculation.patch This patch will later appear in the mm-hotfixes-unstable branch at git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm Before you just go and hit "reply", please: a) Consider who else should be cc'ed b) Prefer to cc a suitable mailing list as well c) Ideally: find the original patch on the mailing list and do a reply-to-all to that, adding suitable additional cc's *** Remember to use Documentation/process/submit-checklist.rst when testing your code *** The -mm tree is included into linux-next via various branches at git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm and is updated there most days ------------------------------------------------------ From: Wang Guangke Subject: mm/damon/stat: avoid overflow in estimated_memory_bandwidth calculation Date: Mon, 9 Nov 2026 16:48:14 -0800 estimated_memory_bandwidth is calculated by access_bytes * USEC_PER_MSEC * MSEC_PER_SEC (= USEC_PER_SEC) / aggr_interval, and users read it via /sys/module/damon_stat/parameters/estimated_memory_bandwidth. On 32-bit systems, access_bytes * USEC_PER_SEC overflows unsigned long once access_bytes exceeds about 4294 (U32_MAX / USEC_PER_SEC), so users get a wrong value. Fix it by doing the calculation in 64-bit and splitting the division into quotient and remainder. The issue was reproduced on a 32-bit system (qemu-system-i386): the parameter estimated_memory_bandwidth reported 362 instead of the expected 1926150; with the fix, the value matches the expectation. Link: https://lore.kernel.org/20261110004816.100066-1-sj@kernel.org Fixes: fabdd1e911da ("mm/damon/stat: calculate and expose estimated memory bandwidth") Signed-off-by: Wang Guangke Signed-off-by: SJ Park Signed-off-by: Andrew Morton Reviewed-by: SJ Park Cc: --- mm/damon/stat.c | 15 +++++++++------ 1 file changed, 9 insertions(+), 6 deletions(-) --- a/mm/damon/stat.c~mm-damon-stat-avoid-overflow-in-estimated_memory_bandwidth-calculation +++ a/mm/damon/stat.c @@ -32,8 +32,8 @@ static bool enabled __read_mostly = IS_E module_param_cb(enabled, &enabled_param_ops, NULL, 0600); MODULE_PARM_DESC(enabled, "Enable of disable DAMON_STAT"); -static unsigned long estimated_memory_bandwidth __read_mostly; -module_param(estimated_memory_bandwidth, ulong, 0400); +static u64 estimated_memory_bandwidth __read_mostly; +module_param(estimated_memory_bandwidth, ullong, 0400); MODULE_PARM_DESC(estimated_memory_bandwidth, "Estimated memory bandwidth usage in bytes per second"); @@ -55,15 +55,18 @@ static void damon_stat_set_estimated_mem { struct damon_target *t; struct damon_region *r; - unsigned long access_bytes = 0; + u64 access_bytes = 0; + u64 remainder, bytes_per_us; damon_for_each_target(t, c) { damon_for_each_region(r, t) - access_bytes += (r->ar.end - r->ar.start) * + access_bytes += (u64)(r->ar.end - r->ar.start) * r->nr_accesses; } - estimated_memory_bandwidth = access_bytes * USEC_PER_MSEC * - MSEC_PER_SEC / c->attrs.aggr_interval; + bytes_per_us = div64_u64_rem(access_bytes, + c->attrs.aggr_interval, &remainder); + estimated_memory_bandwidth = bytes_per_us * USEC_PER_SEC + + div64_u64(remainder * USEC_PER_SEC, c->attrs.aggr_interval); } static int damon_stat_idletime(const struct damon_region *r) _ Patches currently in -mm which might be from gkwang@linx-info.com are mm-damon-stat-avoid-overflow-in-estimated_memory_bandwidth-calculation.patch