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 B3EB8C433EF for ; Tue, 26 Apr 2022 08:42:58 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id 0EEDE6B0073; Tue, 26 Apr 2022 04:42:58 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 09E5A6B0074; Tue, 26 Apr 2022 04:42:58 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id E81216B0075; Tue, 26 Apr 2022 04:42:57 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (relay.hostedemail.com [64.99.140.26]) by kanga.kvack.org (Postfix) with ESMTP id D9EA06B0073 for ; Tue, 26 Apr 2022 04:42:57 -0400 (EDT) Received: from smtpin25.hostedemail.com (a10.router.float.18 [10.200.18.1]) by unirelay11.hostedemail.com (Postfix) with ESMTP id A6A2E80B84 for ; Tue, 26 Apr 2022 08:42:57 +0000 (UTC) X-FDA: 79398389994.25.05B44C4 Received: from mga18.intel.com (mga18.intel.com [134.134.136.126]) by imf25.hostedemail.com (Postfix) with ESMTP id DD668A0042 for ; Tue, 26 Apr 2022 08:42:49 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=intel.com; i=@intel.com; q=dns/txt; s=Intel; t=1650962576; x=1682498576; h=message-id:subject:from:to:cc:date:in-reply-to: references:mime-version:content-transfer-encoding; bh=PCKSkgxENXrIx/upYwDnX/aD/0BDc2Wep/1AmAXydiA=; b=a7D1SJVhJ4opoJqIz/XtmTtCycWBRdVc9p6D721rbf1dzG6xiqqh6cKY dukLlSIA/e+Ap6mz8Guvo7SG/UY3aex9LCM+ELJ0mAMxhZNR2DgNH4LVI C9Xa+ZUPMmDNfOVT5bpTmHRxoxrLg+2TLX60FZlYXCp1LoXfk/umY0HgN UGgHgp1BhNdsYLq9UISwfSvV5dLKJcDdenISpF1EIqc1rDaIIhTwzjeHZ nufI0crknFR8EZBgBkrQvLxwP2PU2jaxG7FgoRbJFuRPxmtnncporwcbP 4w+DaY3EJiZx+YPMAlV48xHbbb6iFkz61R89XTeR2BlG/+UeU1oDyIJBO A==; X-IronPort-AV: E=McAfee;i="6400,9594,10328"; a="247433748" X-IronPort-AV: E=Sophos;i="5.90,290,1643702400"; d="scan'208";a="247433748" Received: from orsmga008.jf.intel.com ([10.7.209.65]) by orsmga106.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 26 Apr 2022 01:42:55 -0700 X-IronPort-AV: E=Sophos;i="5.90,290,1643702400"; d="scan'208";a="579771450" Received: from yyu16-mobl.ccr.corp.intel.com ([10.254.212.128]) by orsmga008-auth.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 26 Apr 2022 01:42:51 -0700 Message-ID: <9a0fe756ae3af78f2612dcf2df9673053a7ebab2.camel@intel.com> Subject: Re: [PATCH v2 0/5] mm: demotion: Introduce new node state N_DEMOTION_TARGETS From: "ying.huang@intel.com" To: Aneesh Kumar K V , Jagdish Gediya , Wei Xu , Yang Shi , Dave Hansen , Dan Williams , Davidlohr Bueso Cc: Linux MM , Linux Kernel Mailing List , Andrew Morton , Baolin Wang , Greg Thelen , MichalHocko , Brice Goglin Date: Tue, 26 Apr 2022 16:42:49 +0800 In-Reply-To: References: <610ccaad03f168440ce765ae5570634f3b77555e.camel@intel.com> <8e31c744a7712bb05dbf7ceb2accf1a35e60306a.camel@intel.com> <78b5f4cfd86efda14c61d515e4db9424e811c5be.camel@intel.com> <200e95cf36c1642512d99431014db8943fed715d.camel@intel.com> <8735i1zurt.fsf@linux.ibm.com> Content-Type: text/plain; charset="UTF-8" User-Agent: Evolution 3.38.3-1 MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Rspam-User: X-Rspamd-Server: rspam11 X-Rspamd-Queue-Id: DD668A0042 X-Stat-Signature: td7no3oeryy3cd6o51zhed9j9t83yer7 Authentication-Results: imf25.hostedemail.com; dkim=pass header.d=intel.com header.s=Intel header.b=a7D1SJVh; spf=none (imf25.hostedemail.com: domain of ying.huang@intel.com has no SPF policy when checking 134.134.136.126) smtp.mailfrom=ying.huang@intel.com; dmarc=pass (policy=none) header.from=intel.com X-HE-Tag: 1650962569-703901 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, 2022-04-25 at 13:39 +0530, Aneesh Kumar K V wrote: > On 4/25/22 11:40 AM, ying.huang@intel.com wrote: > > On Mon, 2022-04-25 at 09:20 +0530, Aneesh Kumar K.V wrote: > > > "ying.huang@intel.com" writes: > > > > > > > Hi, All, > > > > > > > > On Fri, 2022-04-22 at 16:30 +0530, Jagdish Gediya wrote: > > > > > > > > [snip] > > > > > > > > > I think it is necessary to either have per node demotion targets > > > > > configuration or the user space interface supported by this patch > > > > > series. As we don't have clear consensus on how the user interface > > > > > should look like, we can defer the per node demotion target set > > > > > interface to future until the real need arises. > > > > > > > > > > Current patch series sets N_DEMOTION_TARGET from dax device kmem > > > > > driver, it may be possible that some memory node desired as demotion > > > > > target is not detected in the system from dax-device kmem probe path. > > > > > > > > > > It is also possible that some of the dax-devices are not preferred as > > > > > demotion target e.g. HBM, for such devices, node shouldn't be set to > > > > > N_DEMOTION_TARGETS. In future, Support should be added to distinguish > > > > > such dax-devices and not mark them as N_DEMOTION_TARGETS from the > > > > > kernel, but for now this user space interface will be useful to avoid > > > > > such devices as demotion targets. > > > > > > > > > > We can add read only interface to view per node demotion targets > > > > > from /sys/devices/system/node/nodeX/demotion_targets, remove > > > > > duplicated /sys/kernel/mm/numa/demotion_target interface and instead > > > > > make /sys/devices/system/node/demotion_targets writable. > > > > > > > > > > Huang, Wei, Yang, > > > > > What do you suggest? > > > > > > > > We cannot remove a kernel ABI in practice. So we need to make it right > > > > at the first time. Let's try to collect some information for the kernel > > > > ABI definitation. > > > > > > > > The below is just a starting point, please add your requirements. > > > > > > > > 1. Jagdish has some machines with DRAM only NUMA nodes, but they don't > > > > want to use that as the demotion targets. But I don't think this is a > > > > issue in practice for now, because demote-in-reclaim is disabled by > > > > default. > > > > > > It is not just that the demotion can be disabled. We should be able to > > > use demotion on a system where we can find DRAM only NUMA nodes. That > > > cannot be achieved by /sys/kernel/mm/numa/demotion_enabled. It needs > > > something similar to to N_DEMOTION_TARGETS > > > > > > > Can you show NUMA information of your machines with DRAM-only nodes and > > PMEM nodes? We can try to find the proper demotion order for the > > system. If you can not show it, we can defer N_DEMOTION_TARGETS until > > the machine is available. > > > Sure will find one such config. As you might have noticed this is very > easy to have in a virtualization setup because the hypervisor can assign > memory to a guest VM from a numa node that doesn't have CPU assigned to > the same guest. This depends on the other guest VM instance config > running on the system. So on any virtualization config that has got > persistent memory attached, this can become an easy config to end up with. > Why they want to do that? I am looking forward to a real issue, not theoritical possibility. > > > > > 2. For machines with PMEM installed in only 1 of 2 sockets, for example, > > > > > > > > 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 > > > > > > > > We have 2 choices, > > > > > > > > a) > > > > node demotion targets > > > > 0 1 > > > > 2 1 > > > > > > This is achieved by > > > > > > [PATCH v2 1/5] mm: demotion: Set demotion list differently > > > > > > > > > > > b) > > > > node demotion targets > > > > 0 1 > > > > 2 X > > > > > > > > > > > > > > a) is good to take advantage of PMEM. b) is good to reduce cross-socket > > > > traffic. Both are OK as defualt configuration. But some users may > > > > prefer the other one. So we need a user space ABI to override the > > > > default configuration. > > > > > > > > 3. For machines with HBM (High Bandwidth Memory), as in > > > > > > > > https://lore.kernel.org/lkml/39cbe02a-d309-443d-54c9-678a0799342d@gmail.com/ > > > > > > > > > [1] local DDR = 10, remote DDR = 20, local HBM = 31, remote HBM = 41 > > > > > > > > Although HBM has better performance than DDR, in ACPI SLIT, their > > > > distance to CPU is longer. We need to provide a way to fix this. The > > > > user space ABI is one way. The desired result will be to use local DDR > > > > as demotion targets of local HBM. > > > > > > > > > IMHO the above (2b and 3) can be done using per node demotion targets. Below is > > > what I think we could do with a single slow memory NUMA node 4. > > > > If we can use writable per-node demotion targets as ABI, then we don't > > need N_DEMOTION_TARGETS. > > > Not sure I understand that. Yes, once you have a writeable per node > demotion target it is easy to build any demotion order. Yes. > But that doesn't > mean we should not improve the default unless you have reason to say > that using N_DEMOTTION_TARGETS breaks any existing config. > Becuase N_DEMOTTION_TARGETS is a new kernel ABI to override the default, not the default itself.  [1/5] of this patchset improve the default behavior itself, and I think that's good. Because we must maintain the kernel ABI almost for ever, we need to be careful about adding new ABI and add less if possible. If writable per- node demotion targets can address your issue. Then it's unnecessary to add another redundant kernel ABI for that. > > > /sys/devices/system/node# cat node[0-4]/demotion_targets > > > 4 > > > 4 > > > 4 > > > 4 > > > > > > /sys/devices/system/node# echo 1 > node1/demotion_targets > > > bash: echo: write error: Invalid argument > > > /sys/devices/system/node# cat node[0-4]/demotion_targets > > > 4 > > > 4 > > > 4 > > > 4 > > > > > > /sys/devices/system/node# echo 0 > node1/demotion_targets > > > /sys/devices/system/node# cat node[0-4]/demotion_targets > > > 4 > > > 0 > > > 4 > > > 4 > > > > > > /sys/devices/system/node# echo 1 > node0/demotion_targets > > > bash: echo: write error: Invalid argument > > > /sys/devices/system/node# cat node[0-4]/demotion_targets > > > 4 > > > 0 > > > 4 > > > 4 > > > > > > Disable demotion for a specific node. > > > /sys/devices/system/node# echo > node1/demotion_targets > > > /sys/devices/system/node# cat node[0-4]/demotion_targets > > > 4 > > > > > > 4 > > > 4 > > > > > > Reset demotion to default > > > /sys/devices/system/node# echo -1 > node1/demotion_targets > > > /sys/devices/system/node# cat node[0-4]/demotion_targets > > > 4 > > > 4 > > > 4 > > > 4 > > > > > > When a specific device/NUMA node is used for demotion target via the user interface, it is taken > > > out of other NUMA node targets. > > > > IMHO, we should be careful about interaction between auto-generated and > > overridden demotion order. > > > > yes, we should avoid loop between that. In addition to that, we need to get same result after hot-remove then hot-add the same node. That is, the result should be stable after NOOP. I guess we can just always, - Generate the default demotion order automatically without any overriding. - Apply the overriding, after removing the invalid targets, etc. > But if you agree for the above > ABI we could go ahead and share the implementation code. I think we need to add a way to distinguish auto-generated and overriden demotion targets in the output of nodeX/demotion_targets. Otherwise it looks good to me. Best Regards, Huang, Ying > > > root@ubuntu-guest:/sys/devices/system/node# cat node[0-4]/demotion_targets > > > 4 > > > 4 > > > 4 > > > 4 > > > > > > /sys/devices/system/node# echo 4 > node1/demotion_targets > > > /sys/devices/system/node# cat node[0-4]/demotion_targets > > > > > > 4 > > > > > > > > > > > > If more than one node requies the same demotion target > > > /sys/devices/system/node# echo 4 > node0/demotion_targets > > > /sys/devices/system/node# cat node[0-4]/demotion_targets > > > 4 > > > 4 > > > > > > > > > > > > -aneesh > > > > > > -aneesh