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 E67E2C433EF for ; Thu, 28 Apr 2022 00:56:50 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S239312AbiD1BAA (ORCPT ); Wed, 27 Apr 2022 21:00:00 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:50530 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S230197AbiD1A76 (ORCPT ); Wed, 27 Apr 2022 20:59:58 -0400 Received: from mga11.intel.com (mga11.intel.com [192.55.52.93]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 6E8EDBE24 for ; Wed, 27 Apr 2022 17:56:44 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=intel.com; i=@intel.com; q=dns/txt; s=Intel; t=1651107405; x=1682643405; h=message-id:subject:from:to:cc:date:in-reply-to: references:mime-version:content-transfer-encoding; bh=bTii8rU78HdZ/UWhjpXzrq83u14xeBJWe0Ohqjd2PJU=; b=lEq8FlukVW+XI2bsP404NGWE1ht8ykpVcIvS8g+f2uWTO3WtT1GxxFTj zH83J7ZbQSZGHeTh98fkmzRSQRO1K0SY9y6bbYMzRvkz9q+2j2krF+mu+ XkMLjib0RErkohNyhLrcKFXnOzD7M27imWEicFExp10mKdHQ3yCCP2uAx 6FDKdvwncLwKoOKUkkaDewU/OmFOGdOfA7lTUoc2e4/BJWiUriCae915A o9WqlBqey9AcUU0TCYQAbnyHhhZBu7QaPvl/BXdcxobOEiUZEeHZRgYgK CKaxHXFt6TwcHHFrQmpSqS/tAFUCiF9n0r97grYwvA50CUB9GB8KEh2jp A==; X-IronPort-AV: E=McAfee;i="6400,9594,10330"; a="263707099" X-IronPort-AV: E=Sophos;i="5.90,294,1643702400"; d="scan'208";a="263707099" Received: from orsmga008.jf.intel.com ([10.7.209.65]) by fmsmga102.fm.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 Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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