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 90E82C4332F for ; Thu, 24 Feb 2022 03:32:08 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S229502AbiBXDcf (ORCPT ); Wed, 23 Feb 2022 22:32:35 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:55702 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229437AbiBXDcd (ORCPT ); Wed, 23 Feb 2022 22:32:33 -0500 Received: from mga01.intel.com (mga01.intel.com [192.55.52.88]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 6EFC5159E9E; Wed, 23 Feb 2022 19:32:04 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=intel.com; i=@intel.com; q=dns/txt; s=Intel; t=1645673524; x=1677209524; h=from:to:cc:subject:references:date:in-reply-to: message-id:mime-version; bh=F5EcjioZj5uSNCtFNgSr/dmqOCTfAJkkvl7RheW7RxQ=; b=ZbfB+SpWbOfrLpiNV6UTegH01duh7Uy5UMje+FMAcDn5evbGnKQ6r8lW 7atgbnsteDGQOPFx5YyBr5suz/aTQbpz8FfjXtSCRtyqGb/x5d2lxEFL0 lnon8llpaKLwPCSUTb2IH0ZZglGZKqfOMFmNGjhNyWDZsIDWu0xZ5xK32 MDMXJv4vZy7n+wLqm/k5uKywna16jaw+es4HmZP3imGqt+NckTI+TFTL2 rp35OYKdRmmjTByc93ZMubO7/Hl8UuG/ioF8yQ9ljCkFTl+fMKUdxXDJL THZPyjPVtBw/CQNnZlqsMuT72ZhCTFRA1XOSJ400vW0dJl091Bfu+2oCt Q==; X-IronPort-AV: E=McAfee;i="6200,9189,10267"; a="276765559" X-IronPort-AV: E=Sophos;i="5.88,392,1635231600"; d="scan'208";a="276765559" Received: from orsmga005.jf.intel.com ([10.7.209.41]) by fmsmga101.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 23 Feb 2022 19:32:04 -0800 X-IronPort-AV: E=Sophos;i="5.88,392,1635231600"; d="scan'208";a="707298780" Received: from yhuang6-desk2.sh.intel.com (HELO yhuang6-desk2.ccr.corp.intel.com) ([10.239.13.11]) by orsmga005-auth.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 23 Feb 2022 19:31:55 -0800 From: "Huang, Ying" To: Yu Zhao Cc: Andrew Morton , Johannes Weiner , Mel Gorman , Michal Hocko , Andi Kleen , Aneesh Kumar , Barry Song <21cnbao@gmail.com>, Catalin Marinas , Dave Hansen , Hillf Danton , Jens Axboe , Jesse Barnes , Jonathan Corbet , Linus Torvalds , Matthew Wilcox , Michael Larabel , Mike Rapoport , Rik van Riel , Vlastimil Babka , Will Deacon , Linux ARM , "open list:DOCUMENTATION" , linux-kernel , Linux-MM , Kernel Page Reclaim v2 , "the arch/x86 maintainers" , Brian Geffon , Jan Alexander Steffens , Oleksandr Natalenko , Steven Barrett , Suleiman Souhlal , Daniel Byrne , Donald Carr , Holger =?utf-8?Q?Hoffst=C3=A4tte?= , Konstantin Kharlamov , Shuang Zhai , Sofia Trinh Subject: Re: [PATCH v7 05/12] mm: multigenerational LRU: minimal implementation References: <20220208081902.3550911-1-yuzhao@google.com> <20220208081902.3550911-6-yuzhao@google.com> <87bkyy56nv.fsf@yhuang6-desk2.ccr.corp.intel.com> <87y2213wrl.fsf@yhuang6-desk2.ccr.corp.intel.com> Date: Thu, 24 Feb 2022 11:31:53 +0800 In-Reply-To: (Yu Zhao's message of "Wed, 23 Feb 2022 18:34:33 -0700") Message-ID: <87h78p3pp2.fsf@yhuang6-desk2.ccr.corp.intel.com> User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/27.1 (gnu/linux) MIME-Version: 1.0 Content-Type: text/plain; charset=ascii Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Yu Zhao writes: > On Wed, Feb 23, 2022 at 5:59 PM Huang, Ying wrote: >> >> Yu Zhao writes: >> >> > On Wed, Feb 23, 2022 at 1:28 AM Huang, Ying wrote: >> >> >> >> Hi, Yu, >> >> >> >> Yu Zhao writes: >> >> >> >> > To avoid confusions, the terms "promotion" and "demotion" will be >> >> > applied to the multigenerational LRU, as a new convention; the terms >> >> > "activation" and "deactivation" will be applied to the active/inactive >> >> > LRU, as usual. >> >> >> >> In the memory tiering related commits and patchset, for example as follows, >> >> >> >> commit 668e4147d8850df32ca41e28f52c146025ca45c6 >> >> Author: Yang Shi >> >> Date: Thu Sep 2 14:59:19 2021 -0700 >> >> >> >> mm/vmscan: add page demotion counter >> >> >> >> https://lore.kernel.org/linux-mm/20220221084529.1052339-1-ying.huang@intel.com/ >> >> >> >> "demote" and "promote" is used for migrating pages between different >> >> types of memory. Is it better for us to avoid overloading these words >> >> too much to avoid the possible confusion? >> > >> > Given that LRU and migration are usually different contexts, I think >> > we'd be fine, unless we want a third pair of terms. >> >> This is true before memory tiering is introduced. In systems with >> multiple types memory (called memory tiering), LRU is used to identify >> pages to be migrated to the slow memory node. Please take a look at >> can_demote(), which is called in shrink_page_list(). > > This sounds clearly two contexts to me. Promotion/demotion (move > between generations) while pages are on LRU; or promotion/demotion > (migration between nodes) after pages are taken off LRU. > > Note that promotion/demotion are not used in function names. They are > used to describe how MGLRU works, in comparison with the > active/inactive LRU. Memory tiering is not within this context. Because we have used pgdemote_* in /proc/vmstat, "demotion_enabled" in /sys/kernel/mm/numa, and will use pgpromote_* in /proc/vmstat. It seems better to avoid to use promote/demote directly for MGLRU in ABI. A possible solution is to use "mglru" and "promote/demote" together (such as "mglru_promote_*" when it is needed? >> >> > +static int get_swappiness(struct mem_cgroup *memcg) >> >> > +{ >> >> > + return mem_cgroup_get_nr_swap_pages(memcg) >= MIN_LRU_BATCH ? >> >> > + mem_cgroup_swappiness(memcg) : 0; >> >> > +} >> >> >> >> After we introduced demotion support in Linux kernel. The anonymous >> >> pages in the fast memory node could be demoted to the slow memory node >> >> via the page reclaiming mechanism as in the following commit. Can you >> >> consider that too? >> > >> > Sure. How do I check whether there is still space on the slow node? >> >> You can always check the watermark of the slow node. But now, we >> actually don't check that (as in demote_page_list()), instead we will >> wake up kswapd of the slow node. The intended behavior is something >> like, >> >> DRAM -> PMEM -> disk > > I'll look into this later -- for now, it's a low priority because > there isn't much demand. I'll bump it up if anybody is interested in > giving it a try. Meanwhile, please feel free to cook up something if > you are interested. When we introduce a new feature, we shouldn't break an existing one. That is, not introducing regression. I think that it is a rule? If my understanding were correct, MGLRU will ignore to scan anonymous page list even if there's demotion target for the node. This breaks the demotion feature in the upstream kernel. Right? It's a new feature to check whether there is still space on the slow node. We can look at that later. Best Regards, Huang, Ying