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 kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by smtp.lore.kernel.org (Postfix) with ESMTP id 10CCAC433EF for ; Tue, 26 Apr 2022 10:38:01 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id 1A7B36B0073; Tue, 26 Apr 2022 06:38:01 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 12F996B0074; Tue, 26 Apr 2022 06:38:01 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id F12426B0075; Tue, 26 Apr 2022 06:38:00 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (relay.hostedemail.com [64.99.140.27]) by kanga.kvack.org (Postfix) with ESMTP id DB2566B0073 for ; Tue, 26 Apr 2022 06:38:00 -0400 (EDT) Received: from smtpin05.hostedemail.com (a10.router.float.18 [10.200.18.1]) by unirelay13.hostedemail.com (Postfix) with ESMTP id BA6E060EA7 for ; Tue, 26 Apr 2022 10:38:00 +0000 (UTC) X-FDA: 79398679920.05.5348D72 Received: from frasgout.his.huawei.com (frasgout.his.huawei.com [185.176.79.56]) by imf13.hostedemail.com (Postfix) with ESMTP id 22E2320044 for ; Tue, 26 Apr 2022 10:37:53 +0000 (UTC) Received: from fraeml744-chm.china.huawei.com (unknown [172.18.147.200]) by frasgout.his.huawei.com (SkyGuard) with ESMTP id 4KndXQ0PCPz6F94R; Tue, 26 Apr 2022 18:33:58 +0800 (CST) Received: from lhreml710-chm.china.huawei.com (10.201.108.61) by fraeml744-chm.china.huawei.com (10.206.15.225) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256) id 15.1.2375.24; Tue, 26 Apr 2022 12:37:57 +0200 Received: from localhost (10.202.226.42) by lhreml710-chm.china.huawei.com (10.201.108.61) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256) id 15.1.2375.24; Tue, 26 Apr 2022 11:37:56 +0100 Date: Tue, 26 Apr 2022 11:37:55 +0100 From: Jonathan Cameron To: Aneesh Kumar K V CC: Jagdish Gediya , "ying.huang@intel.com" , , , , , , , , , Subject: Re: [PATCH v3 0/7] mm: demotion: Introduce new node state N_DEMOTION_TARGETS Message-ID: <20220426113755.00004721@Huawei.com> In-Reply-To: <132150b3-73f8-ea94-2839-91b92e5d2991@linux.ibm.com> References: <20220422195516.10769-1-jvgediya@linux.ibm.com> <4b986b46afb2fe888c127d8758221d0f0d3ec55f.camel@intel.com> <20220425145735.000007ca@Huawei.com> <132150b3-73f8-ea94-2839-91b92e5d2991@linux.ibm.com> Organization: Huawei Technologies Research and Development (UK) Ltd. X-Mailer: Claws Mail 4.0.0 (GTK+ 3.24.29; i686-w64-mingw32) MIME-Version: 1.0 Content-Type: text/plain; charset="US-ASCII" Content-Transfer-Encoding: 7bit X-Originating-IP: [10.202.226.42] X-ClientProxiedBy: lhreml731-chm.china.huawei.com (10.201.108.82) To lhreml710-chm.china.huawei.com (10.201.108.61) X-CFilter-Loop: Reflected X-Stat-Signature: yh1n3d9qp5axwzryr94khhykwh3b3mt8 X-Rspamd-Server: rspam07 X-Rspamd-Queue-Id: 22E2320044 X-Rspam-User: Authentication-Results: imf13.hostedemail.com; dkim=none; spf=pass (imf13.hostedemail.com: domain of jonathan.cameron@huawei.com designates 185.176.79.56 as permitted sender) smtp.mailfrom=jonathan.cameron@huawei.com; dmarc=pass (policy=quarantine) header.from=huawei.com X-HE-Tag: 1650969473-53401 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On Mon, 25 Apr 2022 20:23:56 +0530 Aneesh Kumar K V wrote: > On 4/25/22 7:27 PM, Jonathan Cameron wrote: > > On Mon, 25 Apr 2022 16:45:38 +0530 > > Jagdish Gediya wrote: > > > > .... > > >> $ numactl -H > >> available: 2 nodes (0-1) > >> node 0 cpus: 0 1 2 3 4 5 6 7 > >> node 0 size: 14272 MB > >> node 0 free: 13392 MB > >> node 1 cpus: > >> node 1 size: 2028 MB > >> node 1 free: 1971 MB > >> node distances: > >> node 0 1 > >> 0: 10 40 > >> 1: 40 10 > >> > >> 1) without N_DEMOTION_TARGETS patch series, 1 is demotion target > >> for 0 even when 1 is DRAM node and there is no demotion targets for 1. > > > > I'm not convinced the distinction between DRAM and persistent memory is > > valid. There will definitely be systems with a large pool > > of remote DRAM (and potentially no NV memory) where the right choice > > is to demote to that DRAM pool. > > > > Basing the decision on whether the memory is from kmem or > > normal DRAM doesn't provide sufficient information to make the decision. > > > >> > >> $ cat /sys/bus/nd/devices/dax0.0/target_node > >> 2 > >> $ > >> # cd /sys/bus/dax/drivers/ > >> :/sys/bus/dax/drivers# ls > >> device_dax kmem > >> :/sys/bus/dax/drivers# cd device_dax/ > >> :/sys/bus/dax/drivers/device_dax# echo dax0.0 > unbind > >> :/sys/bus/dax/drivers/device_dax# echo dax0.0 > ../kmem/new_id > >> :/sys/bus/dax/drivers/device_dax# numactl -H > >> available: 3 nodes (0-2) > >> node 0 cpus: 0 1 2 3 4 5 6 7 > >> node 0 size: 14272 MB > >> node 0 free: 13380 MB > >> node 1 cpus: > >> node 1 size: 2028 MB > >> node 1 free: 1961 MB > >> node 2 cpus: > >> node 2 size: 0 MB > >> node 2 free: 0 MB > >> node distances: > >> node 0 1 2 > >> 0: 10 40 80 > >> 1: 40 10 80 > >> 2: 80 80 10 > >> > >> 2) Once this new node brought online, without N_DEMOTION_TARGETS > >> patch series, 1 is demotion target for 0 and 2 is demotion target > >> for 1. > >> > >> With this patch series applied, > >> 1) No demotion target for either 0 or 1 before dax device is online > > > > I'd argue that is wrong. At this state you have a tiered memory system > > be it one with just DRAM. Using it as such is correct behavior that > > we should not be preventing. Sure some usecases wouldn't want that > > arrangement but some do want it. > > > > I missed this in my earlier reply. Are you suggesting that we would want > Node 1 (DRAM only memory numa node) to act as demotion target for Node > 0? Any reason why we would want to do that? That is clearly opposite of > what we are trying to do here. IMHO node using Node1 as demotion target > for Node0 is a better default? In this case, because of the small size that probably wouldn't make sense. But, if that were a CXL memory pool with multiple TB of DDR then yes we would want the default case to use that memory for the demotion path. So I don't think DDR vs NV via kmem alone is the right basis for a decision on the default behavior. Sure we can make this all a userspace problem. Jonathan > > > > -aneesh