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 82FC8C02198 for ; Mon, 10 Feb 2025 06:00:09 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id C4B496B007B; Mon, 10 Feb 2025 01:00:08 -0500 (EST) Received: by kanga.kvack.org (Postfix, from userid 40) id BFAC36B0083; Mon, 10 Feb 2025 01:00:08 -0500 (EST) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id A9A4C6B0085; Mon, 10 Feb 2025 01:00:08 -0500 (EST) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0016.hostedemail.com [216.40.44.16]) by kanga.kvack.org (Postfix) with ESMTP id 854376B007B for ; Mon, 10 Feb 2025 01:00:08 -0500 (EST) Received: from smtpin30.hostedemail.com (a10.router.float.18 [10.200.18.1]) by unirelay05.hostedemail.com (Postfix) with ESMTP id 3082345E8F for ; Mon, 10 Feb 2025 06:00:08 +0000 (UTC) X-FDA: 83102984496.30.C5FA346 Received: from mail-qk1-f180.google.com (mail-qk1-f180.google.com [209.85.222.180]) by imf12.hostedemail.com (Postfix) with ESMTP id 4A8E54000D for ; Mon, 10 Feb 2025 06:00:06 +0000 (UTC) Authentication-Results: imf12.hostedemail.com; dkim=pass header.d=gourry.net header.s=google header.b=FKYAxE8N; spf=pass (imf12.hostedemail.com: domain of gourry@gourry.net designates 209.85.222.180 as permitted sender) smtp.mailfrom=gourry@gourry.net; dmarc=none ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1739167206; a=rsa-sha256; cv=none; b=QBcukJJxX+9SghaemC4jIsExhMW4dd8iCxHrT+E5MetP0uW3OPgKZGStPs88VJ1iIPzhNk pns4ctM8vLSNZz9ZW4Ef9p6Bi2YhjGvHluy+GEdrAlUYWFW/xv0lOJ6UlxXHBUC6/rpx/R jda9/N1xiwUz/UawoZeT1rFSeYXa9sU= ARC-Authentication-Results: i=1; imf12.hostedemail.com; dkim=pass header.d=gourry.net header.s=google header.b=FKYAxE8N; spf=pass (imf12.hostedemail.com: domain of gourry@gourry.net designates 209.85.222.180 as permitted sender) smtp.mailfrom=gourry@gourry.net; dmarc=none ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1739167206; h=from:from:sender:reply-to:subject:subject:date:date: message-id:message-id:to:to:cc:cc:mime-version:mime-version: content-type:content-type:content-transfer-encoding: in-reply-to:in-reply-to:references:references:dkim-signature; bh=amAQ/fip1zjjPAFrEnkAcUMSCHVM3BmAahoIJR9K7hU=; b=LyZx/tT9lavMRkah/UeMGKVcBbarBy6mDaTBD87miU2nwFkpGXp9IAp20J7Y2lPo9rFv8d ij/k+uxxKwkGJY9eoOKsEu9AqWhar+ZAHIvxQhrDFBbDQ6Pbde7OAXWYduYS0Z7JEliHzy 7r2Xks+5oaCQveJNvqmF7vIVI/TZYKA= Received: by mail-qk1-f180.google.com with SMTP id af79cd13be357-7bcf33f698dso369931385a.2 for ; Sun, 09 Feb 2025 22:00:05 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gourry.net; s=google; t=1739167205; x=1739772005; darn=kvack.org; h=in-reply-to:content-disposition:mime-version:references:message-id :subject:cc:to:from:date:from:to:cc:subject:date:message-id:reply-to; bh=amAQ/fip1zjjPAFrEnkAcUMSCHVM3BmAahoIJR9K7hU=; b=FKYAxE8NPCv85QDE2KS5Wfs98WZa1/9h1qqVP86Fr9951plBfNoP0PYjl4R/ONFtvB ELoE/tCqrzsq1tGxFZkQO5cjclQ6drKHu+yJQ5HgYYdQyaLneOBP1KO6nEGbnmiq05zq /RAQaChHW6YJMErtF/90kUPGIyjgbLHAsvlwkEGZrfVxbGJA1ksPpIuFzRe+0Cfzp8PT kKgi2FjS8H3pXULspe5XcKjf7HghwvI8jHm1cnWemMmUniq8UnNCBAS3vDLO+0p6pYBu TMylMdS1gLOYw7EexRPXg78svPVEwmPJNmnv8Osu7hMac0JS8Mb7CroDbMbR+OD5RF0+ hb7w== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20230601; t=1739167205; x=1739772005; h=in-reply-to:content-disposition:mime-version:references:message-id :subject:cc:to:from:date:x-gm-message-state:from:to:cc:subject:date :message-id:reply-to; bh=amAQ/fip1zjjPAFrEnkAcUMSCHVM3BmAahoIJR9K7hU=; b=Cl9huRCRlhze+3EKpqYTYDttxeiOT2srceKCv1qyoAQEGYyuMf4I00CziHm4y9viSt kgE7E4eWWhMKmvsbXJKqV3/D3kwI+bBk5Ri855ugu9mnFMktLLMXFHTXXJkG97d2mZQd o7sV3UUNsT4GmoLDg4OU2fFQDZrNcE3KZ9xzGDQAuI1QNEZ8T/l/UN8Jh+9y69QFMUoe x0Jsc5Rt9iVRoUwJLdmmbIlw7sioVkHhUgaOoLPGXvS69vhXRyN0KrstrnvVenqZpUZY U/gzbO4yu6qAZ/CEFgmy5nE7bNBof3JzJmUXxpqkemKC6aXZbMRGpkFnVQ9/kzNqajTB QjuQ== X-Forwarded-Encrypted: i=1; AJvYcCW1db95WEP9kBRWezWrKyRTCbPOTwP1GdDq+0dAvOSd2860KhopdshdsYkxeYsR1mr4dIBXJa0eUw==@kvack.org X-Gm-Message-State: AOJu0YyyYmQ8hkiFaLyrJXHMv+Xa4TMHXHDRXdnmmiVPs0d1F1ncS0pd n9nqsmA5+/VTnMKZiwtZajh2HhZV0YxWFUUEeLELhQ16FwifCKCZKB3FIdGET/o= X-Gm-Gg: ASbGncsE097Y6gpyksd0x39t+uKv5Hl7To/1kI7fkfIKxOo1WXX4v7dy+umVguJpJCI NZ77g5Ipw43y7jPQZRmJhui/GPDxYkA5XIlDOu6+IhIoTq3JOUX6uHdXOdxHbVKbNurUveXtKb7 kF4w1Vc2mMoMi62fTN1GbXnNmzVRvu4WJQOU1hRQ6R35agMXs9HWGvx53Cw6+6aO7GhgG2/3GOJ JS83vVVGfSTiMl6btv+hVHw1wMEFE/ptlyH8QL/dqmkNAxT5f/e9HBvHKbkMvZtm5zGBmQvBIih WsC+XtF8Dnb6dz7iKJgP6xFO0oQP0LiwXEoq3c0W7z+N3g02/ifdfGZHpZF833OBsGdcU+EoaQ= = X-Google-Smtp-Source: AGHT+IHhwRLl2TltpPoSTD0m1jyHAGjWZCwGLbFlLxrmsv3fIf/VYYOQNaeDAvY04Qt2kVJcxb3hLQ== X-Received: by 2002:a05:620a:f14:b0:7b1:5763:4ba2 with SMTP id af79cd13be357-7c047c7504dmr2264001985a.40.1739167205217; Sun, 09 Feb 2025 22:00:05 -0800 (PST) Received: from gourry-fedora-PF4VCD3F (pool-173-79-56-208.washdc.fios.verizon.net. [173.79.56.208]) by smtp.gmail.com with ESMTPSA id af79cd13be357-7c04e111a58sm257668385a.92.2025.02.09.22.00.03 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Sun, 09 Feb 2025 22:00:04 -0800 (PST) Date: Mon, 10 Feb 2025 01:00:02 -0500 From: Gregory Price To: "Harry (Hyeonggon) Yoo" <42.hyeyoo@gmail.com> Cc: Honggyu Kim , Byungchul Park , kernel_team@skhynix.com, Matthew Wilcox , lsf-pc@lists.linux-foundation.org, linux-mm@kvack.org, linux-cxl@vger.kernel.org Subject: Re: [LSF/MM/BPF TOPIC] Restricting or migrating unmovable kernel allocations from slow tier Message-ID: References: <20250207072024.GA48419@system.software.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Rspamd-Queue-Id: 4A8E54000D X-Stat-Signature: yuf4xrs6qbb4n7at3qqp3gqz7u4nzqzn X-Rspam-User: X-Rspamd-Server: rspam10 X-HE-Tag: 1739167206-405957 X-HE-Meta: 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 1DXwgRIt pwo5oQIYWJf+58Uyl7yUTV7ClYNLylMBtqHoRItFvr4KNoClxyC4qG434j49NxYKXijuwq5b+3IUN5pa0Zxopgz+gGbKXhRwoaIeMayy180p45nlXaj47h41xs1C33oGfAudjhJEqwM7VdKeTw3H7s9+FdVMiK9C69imuoHxsa/XNnzORcLuYq9GS2tmCE68c8YlfQuC+3IryrVAwLRFgdVfvzFtjOhlNZw/sz/ygoqFYwvmE6nTRmHAdGIMgLSHoV7llIOytdu2RSi5byuvJvB6oXdaWjllKsrbDTytL0riPwomdsOtWjaBlhQKozWXFgBTVmdAYc/jh+n22l1XbMjlMb0MpYzDFcG+912WgyR9jLLHwP+EmDF3fEk60FnBYox5YweLK5ZuF41k= X-Bogosity: Ham, tests=bogofilter, spamicity=0.000074, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Mon, Feb 10, 2025 at 11:33:47AM +0900, Harry (Hyeonggon) Yoo wrote: > > Premise: Some ZONE_NORMAL capacity exists on CXL memory > due to its large capacity. > What you actually need to show to justify increasing the complexity is (at least - but not limited to) 1) structures you want to migrate are harmful when placed on slow memory ex) Is `struct page` on slow mem actually harmful? - no data? ex) Are page tables on slow mem actually harmful? - known, yes. 2) The structures cannot be made to take up less space on local tier ex) struct page can be shrunk - do that first ex) huge-pages can be deployed - do that first 3) the structures take up sufficient space that it matters ex) struct page after shrunk might not - do that first ex) page tables with multi-sized huge pages may not - do that first 4) Making the structures migratable actually does something useful are `struct page` or page tables after #2 and #3 both: a) going through hot/cold phases enough to warrant being tiered b) hot enough for long enough that migration matters? You can probably actually (maybe?) collect data on this today - but you still have to contend with #2 and #3. > > I don't understand why we shouldn't introduce more kernel movable memory > if that turns out to be beneficial? > No one is going to stop research you want to do. I'm simply expressing that I think it's an ill-advised path to take. ~Gregory