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 23D1BC433F5 for ; Thu, 28 Apr 2022 00:56:49 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id 5930C6B0071; Wed, 27 Apr 2022 20:56:49 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 5429D6B0072; Wed, 27 Apr 2022 20:56:49 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 3BCB06B0073; Wed, 27 Apr 2022 20:56:49 -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 2F30D6B0071 for ; Wed, 27 Apr 2022 20:56:49 -0400 (EDT) Received: from smtpin15.hostedemail.com (a10.router.float.18 [10.200.18.1]) by unirelay10.hostedemail.com (Postfix) with ESMTP id 060BBD10 for ; Thu, 28 Apr 2022 00:56:49 +0000 (UTC) X-FDA: 79404472938.15.40A1574 Received: from mga07.intel.com (mga07.intel.com [134.134.136.100]) by imf02.hostedemail.com (Postfix) with ESMTP id B0B8B80059 for ; Thu, 28 Apr 2022 00:56:44 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=intel.com; i=@intel.com; q=dns/txt; s=Intel; t=1651107408; x=1682643408; h=message-id:subject:from:to:cc:date:in-reply-to: references:mime-version:content-transfer-encoding; bh=bTii8rU78HdZ/UWhjpXzrq83u14xeBJWe0Ohqjd2PJU=; b=Ner2/lgRDqYxrfA9AkfoyNjRugkssVo3WF0ebCSlqRBtXh7Od+ie8v3C 8+n970K58gwuP9tp6iG/szpGtL4BgCAZvy8OUBbGpMUsUGkyAAevnqgxW PdS94MVlRvIL+GrtY73Z5alRfInuCtUDwz5NIRnwB0/wUWAUgqDM15Nob OJnjdTihK4WyR6YG3ScDAffi/FLpv07Nwj1NDshnaKhovlLZE67oBQkTk VV1MUUqGocCJQ2ljr6ZmpMMp8mP4ftySt+JvRQ1l5Qp952JTiPRj7Z5cD uvM1NiuzmZETPAixcmAHXjMDfrzjWuP4HR2BsEIcVlTk4tgG1PJX1zbtd g==; X-IronPort-AV: E=McAfee;i="6400,9594,10330"; a="329063097" X-IronPort-AV: E=Sophos;i="5.90,294,1643702400"; d="scan'208";a="329063097" Received: from orsmga008.jf.intel.com ([10.7.209.65]) by orsmga105.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 27 Apr 2022 17:56:44 -0700 X-IronPort-AV: E=Sophos;i="5.90,294,1643702400"; d="scan'208";a="580941009" 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; 27 Apr 2022 17:56:40 -0700 Message-ID: <9d9ef67127b1e2cf0b6c72f60cb7304dc573c28b.camel@intel.com> Subject: Re: [PATCH v2 0/5] mm: demotion: Introduce new node state N_DEMOTION_TARGETS From: "ying.huang@intel.com" To: Wei Xu , Aneesh Kumar K V Cc: 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 , feng.tang@intel.com Date: Thu, 28 Apr 2022 08:56:37 +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: rspam04 X-Rspamd-Queue-Id: B0B8B80059 X-Stat-Signature: 5qiijh353yo47dprs8twuqhcam88zj9c X-Rspam-User: Authentication-Results: imf02.hostedemail.com; dkim=pass header.d=intel.com header.s=Intel header.b="Ner2/lgR"; spf=none (imf02.hostedemail.com: domain of ying.huang@intel.com has no SPF policy when checking 134.134.136.100) smtp.mailfrom=ying.huang@intel.com; dmarc=pass (policy=none) header.from=intel.com X-HE-Tag: 1651107404-8144 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 11:27 -0700, Wei Xu wrote: > On Tue, Apr 26, 2022 at 10:06 PM Aneesh Kumar K V > wrote: > > > > On 4/25/22 10:26 PM, Wei Xu wrote: > > > On Sat, Apr 23, 2022 at 8:02 PM ying.huang@intel.com > > > wrote: > > > > > > > > .... > > > > > > 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). > > > > > > 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. > > > > > > > I have been wondering how we would handle this. For ex: If an > > application has specified an MPOL_BIND policy and restricted the > > allocation to be from Node0 and Node1, should we demote pages allocated > > by that application > > to Node10? The other alternative for that demotion is swapping. So from > > the page point of view, we either demote to a slow memory or pageout to > > swap. But then if we demote we are also breaking the MPOL_BIND rule. > > IMHO, the MPOL_BIND policy should be respected and demotion should be > skipped in such cases. Such MPOL_BIND policies can be an important > tool for applications to override and control their memory placement > when transparent memory tiering is enabled. If the application > doesn't want swapping, there are other ways to achieve that (e.g. > mlock, disabling swap globally, setting memcg parameters, etc). > > > > The above says we would need some kind of mem policy interaction, but > > what I am not sure about is how to find the memory policy in the > > demotion path. > > This is indeed an important and challenging problem. One possible > approach is to retrieve the allowed demotion nodemask from > page_referenced() similar to vm_flags. This works for mempolicy in struct vm_area_struct, but not for that in struct task_struct. Mutiple threads in a process may have different mempolicy. 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. > > > > > > > > -aneesh