From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from frasgout.his.huawei.com (frasgout.his.huawei.com [185.176.79.56]) (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 4E4381F2BB5 for ; Mon, 6 Oct 2025 09:53:51 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=185.176.79.56 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1759744435; cv=none; b=eyt3JuUMTcNrimC0WzkWTkti+kVsAvMNIhPjjDOmDpK4Mycj/ApNWdgAG8e9rs10YGmSCryrqYw+Ce6trdTc/i8ApHyx+Ep6RX0liKDUUPklqt5ZIzPB/Z8WEsPqprfzLRVMc6lSkPs3DenV4uwYi0MJO590ZBpxbaalm6OA8/Q= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1759744435; c=relaxed/simple; bh=NFKU/d1VNslHPHjRed4LBghQn+v8hjBZCkuybwQb9Vc=; h=Date:From:To:CC:Subject:Message-ID:In-Reply-To:References: MIME-Version:Content-Type; b=gMHsNB4Nr9cqrUb2Af/k2REG7A11iUO2DY6o4rRo/v8s2h4TtAqtOD+6KnmGbseGfr8VsRGfZpMpfVNDLZfrm1bwLann0XR/KBYia96Wm2+inGBfe5cMUxnsqrcKjlKCu8JFYAtOMptUMzaDIZgnDqqkM6dRz3pfvTPsoRnXFAI= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=quarantine dis=none) header.from=huawei.com; spf=pass smtp.mailfrom=huawei.com; arc=none smtp.client-ip=185.176.79.56 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=quarantine dis=none) header.from=huawei.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=huawei.com Received: from mail.maildlp.com (unknown [172.18.186.216]) by frasgout.his.huawei.com (SkyGuard) with ESMTP id 4cgF2P1b5Dz6L51s; Mon, 6 Oct 2025 17:53:17 +0800 (CST) Received: from dubpeml100005.china.huawei.com (unknown [7.214.146.113]) by mail.maildlp.com (Postfix) with ESMTPS id CFE04140276; Mon, 6 Oct 2025 17:53:49 +0800 (CST) Received: from localhost (10.203.177.15) by dubpeml100005.china.huawei.com (7.214.146.113) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.2.1544.11; Mon, 6 Oct 2025 10:53:48 +0100 Date: Mon, 6 Oct 2025 10:53:46 +0100 From: Jonathan Cameron To: Bharata B Rao CC: , , , , , , , , , , , , , , , , , , , , , , , , , , , Subject: Re: [RFC PATCH v2 8/8] mm: sched: Move hot page promotion from NUMAB=2 to kpromoted Message-ID: <20251006105346.00004634@huawei.com> In-Reply-To: References: <20250910144653.212066-1-bharata@amd.com> <20250910144653.212066-9-bharata@amd.com> <20251003133818.000017af@huawei.com> X-Mailer: Claws Mail 4.3.0 (GTK 3.24.42; x86_64-w64-mingw32) Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset="US-ASCII" Content-Transfer-Encoding: 7bit X-ClientProxiedBy: lhrpeml100011.china.huawei.com (7.191.174.247) To dubpeml100005.china.huawei.com (7.214.146.113) On Mon, 6 Oct 2025 11:27:21 +0530 Bharata B Rao wrote: > On 03-Oct-25 6:08 PM, Jonathan Cameron wrote: > > On Wed, 10 Sep 2025 20:16:53 +0530 > > Bharata B Rao wrote: > > > >> Currently hot page promotion (NUMA_BALANCING_MEMORY_TIERING > >> mode of NUMA Balancing) does hot page detection (via hint faults), > >> hot page classification and eventual promotion, all by itself and > >> sits within the scheduler. > >> > >> With the new hot page tracking and promotion mechanism being > >> available, NUMA Balancing can limit itself to detection of > >> hot pages (via hint faults) and off-load rest of the > >> functionality to the common hot page tracking system. > >> > >> pghot_record_access(PGHOT_HINT_FAULT) API is used to feed the > >> hot page info. In addition, the migration rate limiting and > >> dynamic threshold logic are moved to kpromoted so that the same > >> can be used for hot pages reported by other sources too. > >> > >> Signed-off-by: Bharata B Rao > > > > Making a direct replacement without any fallback to previous method > > is going to need a lot of data to show there are no important regressions. > > > > So bold move if that's the intent! > > Firstly I am only moving the existing hot page heuristics that is part of > NUMAB=2 to kpromoted so that the same can be applied to hot pages being > identified by other sources. So the hint fault mechanism that is inherent > to NUMAB=2 still remains. That makes sense. > > In fact, kscand effort started as a potential replacement for the existing > hot page promotion mechanism by getting rid of hint faults and moving the > page table scanning out of process context. Understood and I'm in favor of the that approach but not sure it will be a fit for all workloads. > > In any case, I will start including numbers from the next post. Great. > >> > >> static unsigned int sysctl_pghot_freq_window = KPROMOTED_FREQ_WINDOW; > >> > >> +/* Restrict the NUMA promotion throughput (MB/s) for each target node. */ > >> +static unsigned int sysctl_pghot_promote_rate_limit = 65536; > > > > If the comment correlates with the value, this is 64 GiB/s? That seems > > unlikely if I guess possible. > > IIUC, the existing logic tries to limit promotion rate to 64 GiB/s by > limiting the number of candidate pages that are promoted within the > 1s observation interval. > > Are you saying that achieving the rate of 64 GiB/s is not possible > or unlikely? Seem rather too high to me, but maybe I just have the wrong mental model of what we should be moving. > > > > >> + > >> #ifdef CONFIG_SYSCTL > >> static const struct ctl_table pghot_sysctls[] = { > >> { > >> @@ -44,8 +50,17 @@ static const struct ctl_table pghot_sysctls[] = { > >> .proc_handler = proc_dointvec_minmax, > >> .extra1 = SYSCTL_ZERO, > >> }, > >> + { > >> + .procname = "pghot_promote_rate_limit_MBps", > >> + .data = &sysctl_pghot_promote_rate_limit, > >> + .maxlen = sizeof(unsigned int), > >> + .mode = 0644, > >> + .proc_handler = proc_dointvec_minmax, > >> + .extra1 = SYSCTL_ZERO, > >> + }, > >> }; > >> #endif > >> + > > Put that in earlier patch to reduce noise here. > > This patch moves the hot page heuristics to kpromoted and hence this > related sysctl is also being moved in this patch. I just mean the blank line - not the block above. This is just a patch set tidying up comment. Jonathan