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 9A1AEC433F5 for ; Thu, 28 Apr 2022 08:37:41 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id 3AB246B007B; Thu, 28 Apr 2022 04:37:41 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 35B606B007D; Thu, 28 Apr 2022 04:37:41 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 24AB46B007E; Thu, 28 Apr 2022 04:37:41 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (relay.a.hostedemail.com [64.99.140.24]) by kanga.kvack.org (Postfix) with ESMTP id 165776B007B for ; Thu, 28 Apr 2022 04:37:41 -0400 (EDT) Received: from smtpin19.hostedemail.com (a10.router.float.18 [10.200.18.1]) by unirelay08.hostedemail.com (Postfix) with ESMTP id E17A62152B for ; Thu, 28 Apr 2022 08:37:40 +0000 (UTC) X-FDA: 79405634280.19.0FEC02F Received: from mga02.intel.com (mga02.intel.com [134.134.136.20]) by imf17.hostedemail.com (Postfix) with ESMTP id BD98F40058 for ; Thu, 28 Apr 2022 08:37:31 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=intel.com; i=@intel.com; q=dns/txt; s=Intel; t=1651135060; x=1682671060; h=message-id:subject:from:to:cc:date:in-reply-to: references:mime-version:content-transfer-encoding; bh=HwmGF4rIcjwwV8q8uxbE8wsBmcCLazT1Q+3ogCoTicE=; b=lpbvA1pLH6TTtlbH7z+VYgA2Li6cT+VNDsDTTOGcm+HBE792ZblOyN3j x+tOxMubb+s2hAJYQPnHIrGtxGkB6rabe0gAPbFpPHRHRER/wCmn+UcVj 5HdGkeWNp8E8L+xBGlKCcHwMh98kavzZKECTPcSY4/x7Fkq2/2K4KXsL6 3vto7OiGF904XLebc7qjRwnhdTacH9eBCCI18ojuIFv1mlPkb+R67JTP0 BqX8vpccRkxMHetvt5lS2uBu2gVXXoLV/vgZEcosTrQkhapFG7KtGMxjI dJXIFH6hVQrUtb32WF1t6wGi4rh9CssiXnByzgnzJ9KQXcNalvyw1esCy w==; X-IronPort-AV: E=McAfee;i="6400,9594,10330"; a="253589080" X-IronPort-AV: E=Sophos;i="5.90,295,1643702400"; d="scan'208";a="253589080" Received: from orsmga008.jf.intel.com ([10.7.209.65]) by orsmga101.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 28 Apr 2022 01:37:38 -0700 X-IronPort-AV: E=Sophos;i="5.90,295,1643702400"; d="scan'208";a="581158956" Received: from shanlinl-mobl.ccr.corp.intel.com ([10.254.212.81]) by orsmga008-auth.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 28 Apr 2022 01:37:34 -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: Jagdish Gediya , Yang Shi , Dave Hansen , Dan Williams , Davidlohr Bueso , Linux MM , Linux Kernel Mailing List , Andrew Morton , "Aneesh Kumar K.V" , Baolin Wang , Greg Thelen , MichalHocko , Brice Goglin , Tim C Chen Date: Thu, 28 Apr 2022 16:37:32 +0800 In-Reply-To: References: <610ccaad03f168440ce765ae5570634f3b77555e.camel@intel.com> <8e31c744a7712bb05dbf7ceb2accf1a35e60306a.camel@intel.com> <78b5f4cfd86efda14c61d515e4db9424e811c5be.camel@intel.com> <200e95cf36c1642512d99431014db8943fed715d.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 X-Rspamd-Server: rspam02 X-Rspamd-Queue-Id: BD98F40058 X-Stat-Signature: wacgym47eeisrz849qezqhbcjb8j38bn X-Rspam-User: Authentication-Results: imf17.hostedemail.com; dkim=pass header.d=intel.com header.s=Intel header.b=lpbvA1pL; spf=none (imf17.hostedemail.com: domain of ying.huang@intel.com has no SPF policy when checking 134.134.136.20) smtp.mailfrom=ying.huang@intel.com; dmarc=pass (policy=none) header.from=intel.com X-HE-Tag: 1651135051-332453 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 Wed, 2022-04-27 at 09:27 -0700, Wei Xu wrote: > On Wed, Apr 27, 2022 at 12:11 AM ying.huang@intel.com > wrote: > > > > On Mon, 2022-04-25 at 09:56 -0700, Wei Xu wrote: > > > On Sat, Apr 23, 2022 at 8:02 PM ying.huang@intel.com > > > wrote: > > > > > > > > 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. > > > > > > > > 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 > > > > > > > > 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. > > > > > > I think 2(a) should be the system-wide configuration and 2(b) can be > > > achieved with NUMA mempolicy (which needs to be added to demotion). > > > > Unfortunately, some NUMA mempolicy information isn't available at > > demotion time, for example, mempolicy enforced via set_mempolicy() is > > for thread. But I think that cpusets can work for demotion. > > > > > In general, we can view the demotion order in a way similar to > > > allocation fallback order (after all, if we don't demote or demotion > > > lags behind, the allocations will go to these demotion target nodes > > > according to the allocation fallback order anyway). If we initialize > > > the demotion order in that way (i.e. every node can demote to any node > > > in the next tier, and the priority of the target nodes is sorted for > > > each source node), we don't need per-node demotion order override from > > > the userspace. What we need is to specify what nodes should be in > > > each tier and support NUMA mempolicy in demotion. > > > > This sounds interesting. Tier sounds like a natural and general concept > > for these memory types. It's attracting to use it for user space > > interface too. For example, we may use that for mem_cgroup limits of a > > specific memory type (tier). > > > > And if we take a look at the N_DEMOTION_TARGETS again from the "tier" > > point of view. The nodes are divided to 2 classes via > > N_DEMOTION_TARGETS. > > > > - The nodes without N_DEMOTION_TARGETS are top tier (or tier 0). > > > > - The nodes with N_DEMOTION_TARGETS are non-top tier (or tier 1, 2, 3, > > ...) > > > > Yes, this is one of the main reasons why we (Google) want this interface. > > > So, another possibility is to fit N_DEMOTION_TARGETS and its overriding > > into "tier" concept too. !N_DEMOTION_TARGETS == TIER0. > > > > - All nodes start with TIER0 > > > > - TIER0 can be cleared for some nodes via e.g. kmem driver > > > > TIER0 node list can be read or overriden by the user space via the > > following interface, > > > >   /sys/devices/system/node/tier0 > > > > In the future, if we want to customize more tiers, we can add tier1, > > tier2, tier3, ..... For now, we can add just tier0. That is, the > > interface is extensible in the future compared with > > .../node/demote_targets. > > > > This more explicit tier definition interface works, too. > In addition to make tiering definition explicit, more importantly, this makes it much easier to support more than 2 tiers. For example, for a system with HBM (High Bandwidth Memory), CPU+DRAM, DRAM only, and PMEM, that is, 3 tiers, we can put HBM in tier 0, CPU+DRAM and DRAM only in tier 1, and PMEM in tier 2, automatically, or via user space overridding. N_DEMOTION_TARGETS isn't natural to be extended to support this. Best Regards, Huang, Ying > > This isn't as flexible as the writable per-node demotion targets. But > > it may be enough for most requirements? > > I would think so. Besides, it doesn't really conflict with the > per-node demotion target interface if we really want to introduce the > latter. > > > Best Regards, > > Huang, Ying > > > > > Cross-socket demotion should not be too big a problem in practice > > > because we can optimize the code to do the demotion from the local CPU > > > node (i.e. local writes to the target node and remote read from the > > > source node). The bigger issue is cross-socket memory access onto the > > > demoted pages from the applications, which is why NUMA mempolicy is > > > important here. > > > > > > > 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. > > > > > > > > Best Regards, > > > > Huang, Ying > > > > > > > > > >