From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id AB350C433EF for ; Thu, 21 Apr 2022 07:09:01 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1385598AbiDUHLq (ORCPT ); Thu, 21 Apr 2022 03:11:46 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:41108 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1355444AbiDUHLn (ORCPT ); Thu, 21 Apr 2022 03:11:43 -0400 Received: from mga09.intel.com (mga09.intel.com [134.134.136.24]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 1BBD4167CE for ; Thu, 21 Apr 2022 00:08:54 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=intel.com; i=@intel.com; q=dns/txt; s=Intel; t=1650524934; x=1682060934; h=message-id:subject:from:to:cc:date:in-reply-to: references:mime-version:content-transfer-encoding; bh=HaRBg4+XLdpGv2/lsuEUgBRp2eJFtmoR9sNtCjPghKE=; b=PpPdGehbnIYwWFQLm6y6aNovYeU4xkAyPc3uXRlvgvCKv87KrK5xNRHs 8LJQPQxzO/tMK8jOFpK3lZQEzFfpfqGKMDI6q1De/w0HTOwfV6EnJIIMO 9MbSsyYo2gB+FNOO49SdCb2bkPWgUipTRcbewlR8EVGy4Vw8fsuJr/Tbc 4vfTXIgPMc/Dvd/lGxOUgb9h7JRNJlqa04h7u3Ea3LtGXvxoxuzprDmxR F//Y75PLNrUvUk5xBgQnzmLGuxkXqlDa4kRg1u7/zzf9tqY4eNXBNuVcH dsl3M7pxmxsoGzl7S7WZfwY3aSThPMhY6gq7nvbSg5KWae6ROj59BlYlY w==; X-IronPort-AV: E=McAfee;i="6400,9594,10323"; a="263728412" X-IronPort-AV: E=Sophos;i="5.90,278,1643702400"; d="scan'208";a="263728412" Received: from orsmga008.jf.intel.com ([10.7.209.65]) by orsmga102.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 21 Apr 2022 00:08:53 -0700 X-IronPort-AV: E=Sophos;i="5.90,278,1643702400"; d="scan'208";a="577062744" Received: from hanyulon-mobl1.ccr.corp.intel.com ([10.254.214.143]) by orsmga008-auth.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 21 Apr 2022 00:08:50 -0700 Message-ID: Subject: Re: [PATCH v2 0/5] mm: demotion: Introduce new node state N_DEMOTION_TARGETS From: "ying.huang@intel.com" To: Wei Xu Cc: Yang Shi , Jagdish Gediya , Linux MM , Linux Kernel Mailing List , Andrew Morton , "Aneesh Kumar K.V" , Baolin Wang , Dave Hansen , Dan Williams , Greg Thelen Date: Thu, 21 Apr 2022 15:08:48 +0800 In-Reply-To: References: <20220413092206.73974-1-jvgediya@linux.ibm.com> <6365983a8fbd8c325bb18959c51e9417fd821c91.camel@intel.com> Content-Type: text/plain; charset="UTF-8" User-Agent: Evolution 3.38.3-1 MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, 2022-04-20 at 23:49 -0700, Wei Xu wrote: > On Wed, Apr 20, 2022 at 11:24 PM ying.huang@intel.com > wrote: > > > > On Wed, 2022-04-20 at 22:41 -0700, Wei Xu wrote: > > > On Wed, Apr 20, 2022 at 8:12 PM Yang Shi wrote: > > > > > > > > On Thu, Apr 14, 2022 at 12:00 AM ying.huang@intel.com > > > > wrote: > > > > > > > > > > On Wed, 2022-04-13 at 14:52 +0530, Jagdish Gediya wrote: > > > > > > Current implementation to find the demotion targets works > > > > > > based on node state N_MEMORY, however some systems may have > > > > > > dram only memory numa node which are N_MEMORY but not the > > > > > > right choices as demotion targets. > > > > > > > > > > > > This patch series introduces the new node state > > > > > > N_DEMOTION_TARGETS, which is used to distinguish the nodes which > > > > > > can be used as demotion targets, node_states[N_DEMOTION_TARGETS] > > > > > > is used to hold the list of nodes which can be used as demotion > > > > > > targets, support is also added to set the demotion target > > > > > > list from user space so that default behavior can be overridden. > > > > > > > > > > It appears that your proposed user space interface cannot solve all > > > > > problems. For example, for system as follows, > > > > > > > > > > Node 0 & 2 are cpu + dram nodes and node 1 are slow memory node near > > > > > node 0, > > > > > > > > > > available: 3 nodes (0-2) > > > > > node 0 cpus: 0 1 > > > > > node 0 size: n MB > > > > > node 0 free: n MB > > > > > node 1 cpus: > > > > > node 1 size: n MB > > > > > node 1 free: n MB > > > > > node 2 cpus: 2 3 > > > > > node 2 size: n MB > > > > > node 2 free: n MB > > > > > node distances: > > > > > node 0 1 2 > > > > >   0: 10 40 20 > > > > >   1: 40 10 80 > > > > >   2: 20 80 10 > > > > > > > > > > Demotion order 1: > > > > > > > > > > node demotion_target > > > > >  0 1 > > > > >  1 X > > > > >  2 X > > > > > > > > > > Demotion order 2: > > > > > > > > > > node demotion_target > > > > >  0 1 > > > > >  1 X > > > > >  2 1 > > > > > > > > > > The demotion order 1 is preferred if we want to reduce cross-socket > > > > > traffic. While the demotion order 2 is preferred if we want to take > > > > > full advantage of the slow memory node. We can take any choice as > > > > > automatic-generated order, while make the other choice possible via user > > > > > space overridden. > > > > > > > > > > I don't know how to implement this via your proposed user space > > > > > interface. How about the following user space interface? > > > > > > > > > > 1. Add a file "demotion_order_override" in > > > > >         /sys/devices/system/node/ > > > > > > > > > > 2. When read, "1" is output if the demotion order of the system has been > > > > > overridden; "0" is output if not. > > > > > > > > > > 3. When write "1", the demotion order of the system will become the > > > > > overridden mode. When write "0", the demotion order of the system will > > > > > become the automatic mode and the demotion order will be re-generated. > > > > > > > > > > 4. Add a file "demotion_targets" for each node in > > > > >         /sys/devices/system/node/nodeX/ > > > > > > > > > > 5. When read, the demotion targets of nodeX will be output. > > > > > > > > > > 6. When write a node list to the file, the demotion targets of nodeX > > > > > will be set to the written nodes. And the demotion order of the system > > > > > will become the overridden mode. > > > > > > > > TBH I don't think having override demotion targets in userspace is > > > > quite useful in real life for now (it might become useful in the > > > > future, I can't tell). Imagine you manage hundred thousands of > > > > machines, which may come from different vendors, have different > > > > generations of hardware, have different versions of firmware, it would > > > > be a nightmare for the users to configure the demotion targets > > > > properly. So it would be great to have the kernel properly configure > > > > it *without* intervening from the users. > > > > > > > > So we should pick up a proper default policy and stick with that > > > > policy unless it doesn't work well for the most workloads. I do > > > > understand it is hard to make everyone happy. My proposal is having > > > > every node in the fast tier has a demotion target (at least one) if > > > > the slow tier exists sounds like a reasonable default policy. I think > > > > this is also the current implementation. > > > > > > > > > > This is reasonable. I agree that with a decent default policy, > > > > > > > I agree that a decent default policy is important. As that was enhanced > > in [1/5] of this patchset. > > > > > the > > > overriding of per-node demotion targets can be deferred. The most > > > important problem here is that we should allow the configurations > > > where memory-only nodes are not used as demotion targets, which this > > > patch set has already addressed. > > > > Do you mean the user space interface proposed by [3/5] of this patchset? > > Yes. > > > IMHO, if we want to add a user space interface, I think that it should > > be powerful enough to address all existing issues and some potential > > future issues, so that it can be stable. I don't think it's a good idea > > to define a partial user space interface that works only for a specific > > use case and cannot be extended for other use cases. > > I actually think that they can be viewed as two separate problems: one > is to define which nodes can be used as demotion targets (this patch > set), and the other is how to initialize the per-node demotion path > (node_demotion[]). We don't have to solve both problems at the same > time. > > If we decide to go with a per-node demotion path customization > interface to indirectly set N_DEMOTION_TARGETS, I'd prefer that there > is a single global control to turn off all demotion targets (for the > machines that don't use memory-only nodes for demotion). > There's one already. In commit 20b51af15e01 ("mm/migrate: add sysfs interface to enable reclaim migration"), a sysfs interface /sys/kernel/mm/numa/demotion_enabled is added to turn off all demotion targets. Best Regards, Huang, Ying