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 4972EC433FE for ; Wed, 27 Apr 2022 04:27:18 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1357654AbiD0Ea0 (ORCPT ); Wed, 27 Apr 2022 00:30:26 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:43330 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1357635AbiD0EaY (ORCPT ); Wed, 27 Apr 2022 00:30:24 -0400 Received: from mail-vk1-xa2e.google.com (mail-vk1-xa2e.google.com [IPv6:2607:f8b0:4864:20::a2e]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 0C8C113DE0 for ; Tue, 26 Apr 2022 21:27:14 -0700 (PDT) Received: by mail-vk1-xa2e.google.com with SMTP id bc42so365302vkb.12 for ; Tue, 26 Apr 2022 21:27:14 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20210112; h=mime-version:references:in-reply-to:from:date:message-id:subject:to :cc; bh=ZP5hHWgOyitdI74hmT/MtqQOkUerntDv5R3vS847K7c=; b=msHG7B/GXY/y31IUcUaVHCWDF7Hw61PO55rLvlbKp1on35EG8XwTxDQMO6DyFAGTrY ni8A+Qnp9vNN2P9fros/klc7Ws0ffGCc6zOIOuiZe6Ca/tWGyfy5llUgfrilNXwaKpOV toFnsSxxk438vmHEsrURVtNNtv4Bwq8qT01y+M+fTwxj53JV+oKOc3N/GRV1Ren99YHl DtyVD8V2jno/3EcFX9BAKmSX6mPlwM4OA1OXiE/eSm3aUxZL2Y3gY7VOBfIPV4BukeqS jrjJTZw0gX3wSqN65P30/rS0/IpxPAYeKwN0eXVZ1uFtquaArK8+RvuWjaUA7MnvaEeI T1XQ== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; h=x-gm-message-state:mime-version:references:in-reply-to:from:date :message-id:subject:to:cc; bh=ZP5hHWgOyitdI74hmT/MtqQOkUerntDv5R3vS847K7c=; b=ieSXoEHl3fT33WeTKV39ENeImh95X+kdoTgLD69qXTAgEB5fGsb1/m7jATFMqma+0q fab4qnI5Ack9qMT+Av7YFa0C0k0Wt1urFLQE3gpnb+Ivi4am3NwE9qRNW/+/ZoTUXUxh tdVBpyahHJafEk6Ldcs70728fwN3mv4/NDuyhDME+uFLNVAGm8q2dJOkqk4sUMV9DEuI 4TEV+jdjZ7NU5icBW00ZvPn9ogyM12Xuz3fCXSj/6FM+3IU01xCdrlZue9sM6/cn8wBK duQJY3Gmp96KnucOy9cyWIgIppdHvoa8jKRl9VHqWCIQ99uuBh/OaHDPMK+d8ZVh/g+9 /X3w== X-Gm-Message-State: AOAM533JOLGbt1c2m3m2RrTS4Oh590b7eK7ATw/wSaG1My8uftlG9aI+ 8bvI5ua+JjwwobMOOVYYyJXBsYeVFOlIX6H0GRPCSQ== X-Google-Smtp-Source: ABdhPJwvryGFVUfJKXOoOIJLt5p0ocVqbSvHREAnjaOFYYjecqgwQZBPWFSqo1OPWWplBFIbDy7MnB1JhoCooK+S9tg= X-Received: by 2002:a1f:38c2:0:b0:349:9667:9232 with SMTP id f185-20020a1f38c2000000b0034996679232mr8140821vka.16.1651033632966; Tue, 26 Apr 2022 21:27:12 -0700 (PDT) MIME-Version: 1.0 References: <610ccaad03f168440ce765ae5570634f3b77555e.camel@intel.com> <8e31c744a7712bb05dbf7ceb2accf1a35e60306a.camel@intel.com> <78b5f4cfd86efda14c61d515e4db9424e811c5be.camel@intel.com> <200e95cf36c1642512d99431014db8943fed715d.camel@intel.com> <8735i1zurt.fsf@linux.ibm.com> <9a0fe756ae3af78f2612dcf2df9673053a7ebab2.camel@intel.com> In-Reply-To: <9a0fe756ae3af78f2612dcf2df9673053a7ebab2.camel@intel.com> From: Wei Xu Date: Tue, 26 Apr 2022 21:27:01 -0700 Message-ID: Subject: Re: [PATCH v2 0/5] mm: demotion: Introduce new node state N_DEMOTION_TARGETS To: "ying.huang@intel.com" Cc: Aneesh Kumar K V , Jagdish Gediya , Yang Shi , Dave Hansen , Dan Williams , Davidlohr Bueso , Linux MM , Linux Kernel Mailing List , Andrew Morton , Baolin Wang , Greg Thelen , MichalHocko , Brice Goglin Content-Type: text/plain; charset="UTF-8" Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Apr 26, 2022 at 1:43 AM ying.huang@intel.com wrote: > > 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. I still think the kernel should initialize the per-node demotion order in a way similar to allocation fallback order and there is no need for a userspace interface to override per-node demotion order. But I don't object to such a per-node demotion order override interface proposed here. On the other hand, I think it is better to preserve the system-wide /sys/devices/system/node/demotion_targets as writable. If the userspace only wants to specify a specific set of nodes as the demotion tier and is perfectly fine with the per-node demotion order generated by the kernel, why should we enforce the userspace to have to manually define the per-node demotion order as well? > > > > /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 > >