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 22FCB23393F for ; Sun, 30 Aug 2026 05:23:50 +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=1788067432; cv=none; b=f+tmMQvNEJH+DTadw0QjQ7nuvI8Xh/ftM6cGeuYPWHjTQrhlDjTh6izVoU0gdjT6tz6+wbq5UrvWr/hVMUzmVxTD20Db7rtxlx+nOQD0ffb986VsP0aLM1b1vVPxJ6CqmO96UcbNh8I2PRNo6B1zWfR7kKesHA99BtgJggoiRog= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1788067432; c=relaxed/simple; bh=jVLOL2Dt6ATOphZWvaEvoZKvJXCpyfLywS8JhCN8BlA=; h=From:Subject:To:Cc:In-Reply-To:References:Content-Type:Date: Message-Id; b=TXbjgBwPAOmooj6uMVKQVkBqs+pitcoK5J2jDUlvhuEYuKGSyA4DPBpPDA6zdzm38+pE/YPa8/BbfQv9aRE0QCyolCjc5BhU3+REJx9pprd/w8zjurgr8gBtNwSlSlrR0hPa+QBy2oRL9Z+TI9eywVCXM0iEFembQElyY5eFSGA= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=JWzC/lKE; 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="JWzC/lKE" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 909971F000E9; Sun, 30 Aug 2026 05:23:50 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1788067430; bh=6vbyfazQzLMf8uAiHs2quInpNP8lgEIoGl39bxfbhzM=; h=From:Subject:Reply-To:To:Cc:In-Reply-To:References:Date; b=JWzC/lKErxEJM+vs+9JLxVNrzDyDIvw+xH6+eO1g+8G/J2SOFBHPg72MvuF8FdwhQ qzddV50K3drPEHv2/71kn6dOUkEJ2IKAJj0dwAgqsZaGiSWYQkAmoOjVFnhWLLyqqw KHGRGHDq+yJGbkIIBl6egMP48AQN8NnEObZepCfBBdO96ExiSXjeDj/ipCzetMbH7K BfXxcVQqTEEzVmg52fh1RWdnzHtaWYk3Ri9biD1mLDxTtD4qbEKp4c0M8c45NWIpyj QsnEix5Nt8DrGPnwpLb1jwWuqyFxyLfdsgTtaPVp4ObeyAThlNqAlxhqX8+5EK2ZfI 4tEPxg4CXHhMA== From: sashiko-bot@kernel.org Subject: Re: [PATCH 4/6] mm/damon: support flush-assisted access bit clearing for monitoring Reply-To: sashiko-reviews@lists.linux.dev To: "Krishna Iyer" Cc: damon@lists.linux.dev In-Reply-To: <20260830051407.50008-5-kiyer@crusoe.ai> References: <20260830051407.50008-1-kiyer@crusoe.ai> <20260830051407.50008-5-kiyer@crusoe.ai> Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: quoted-printable Date: Sun, 30 Aug 2026 05:23:50 +0000 Message-Id: <20260830052350.909971F000E9@smtp.kernel.org> Precedence: bulk X-Mailing-List: damon@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: > DAMON's access sampling clears the accessed bit of the sampled page and > re-reads it one sampling interval later. The clearing uses the > non-flushing primitives, deliberately trading accuracy for low > overhead: cached TLB translations survive the clearing, and accesses > through such cached translations do not perform page table walks, hence > do not set the accessed bit again. The bit therefore re-arms at the > TLB-refill rate rather than the actual access rate. >=20 > For most setups this is a good trade-off, since TLB pressure re-walks > hot pages frequently anyway. It breaks down when translations are > long-lived, most prominently on virtualization hosts backing guest > memory with 1 GiB hugetlb pages: covering hundreds of GiB takes only > hundreds of TLB entries, translations essentially never get evicted, > and secondary MMU (e.g. KVM/EPT) accessed bits cleared via > mmu_notifier_clear_young() are rarely set again. Measurements on a > [ ... ] >=20 > DAMOS filter paths keep the non-flushing behavior unconditionally. >=20 > Assisted-by: Claude:claude-fable-5 > Signed-off-by: Krishna Iyer Sashiko has reviewed this patch and found no issues. It looks great! --=20 Sashiko AI review =C2=B7 https://sashiko.dev/#/patchset/20260830051407.5000= 8-1-kiyer@crusoe.ai?part=3D4