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 64FA3EB64DD for ; Tue, 27 Jun 2023 09:55:19 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S230373AbjF0JzR (ORCPT ); Tue, 27 Jun 2023 05:55:17 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:52226 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S231829AbjF0Jy4 (ORCPT ); Tue, 27 Jun 2023 05:54:56 -0400 Received: from foss.arm.com (foss.arm.com [217.140.110.172]) by lindbergh.monkeyblade.net (Postfix) with ESMTP id F01AC2942; Tue, 27 Jun 2023 02:54:12 -0700 (PDT) Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id 757662F4; Tue, 27 Jun 2023 02:54:56 -0700 (PDT) Received: from [10.1.30.74] (C02Z41KALVDN.cambridge.arm.com [10.1.30.74]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 8C2303F64C; Tue, 27 Jun 2023 02:54:09 -0700 (PDT) Message-ID: <6fc531bc-6b72-37bd-7380-0969622f08d4@arm.com> Date: Tue, 27 Jun 2023 10:54:08 +0100 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.15; rv:102.0) Gecko/20100101 Thunderbird/102.12.0 Subject: Re: [PATCH v1 08/10] mm: Kconfig hooks to determine max anon folio allocation order To: Yu Zhao Cc: Andrew Morton , "Matthew Wilcox (Oracle)" , "Kirill A. Shutemov" , Yin Fengwei , David Hildenbrand , Catalin Marinas , Will Deacon , Geert Uytterhoeven , Christian Borntraeger , Sven Schnelle , Thomas Gleixner , Ingo Molnar , Borislav Petkov , Dave Hansen , "H. Peter Anvin" , linux-kernel@vger.kernel.org, linux-mm@kvack.org, linux-alpha@vger.kernel.org, linux-arm-kernel@lists.infradead.org, linux-ia64@vger.kernel.org, linux-m68k@lists.linux-m68k.org, linux-s390@vger.kernel.org References: <20230626171430.3167004-1-ryan.roberts@arm.com> <20230626171430.3167004-9-ryan.roberts@arm.com> From: Ryan Roberts In-Reply-To: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 27/06/2023 03:47, Yu Zhao wrote: > On Mon, Jun 26, 2023 at 11:15 AM Ryan Roberts wrote: >> >> For variable-order anonymous folios, we need to determine the order that >> we will allocate. From a SW perspective, the higher the order we >> allocate, the less overhead we will have; fewer faults, fewer folios in >> lists, etc. But of course there will also be more memory wastage as the >> order increases. >> >> From a HW perspective, there are memory block sizes that can be >> beneficial to reducing TLB pressure. arm64, for example, has the ability >> to map "contpte" sized chunks (64K for a 4K base page, 2M for 16K and >> 64K base pages) such that one of these chunks only uses a single TLB >> entry. >> >> So we let the architecture specify the order of the maximally beneficial >> mapping unit when PTE-mapped. Furthermore, because in some cases, this >> order may be quite big (and therefore potentially wasteful of memory), >> allow the arch to specify 2 values; One is the max order for a mapping >> that _would not_ use THP if all size and alignment constraints were met, >> and the other is the max order for a mapping that _would_ use THP if all >> those constraints were met. >> >> Implement this with Kconfig by introducing some new options to allow the >> architecture to declare that it supports large anonymous folios along >> with these 2 preferred max order values. Then introduce a user-facing >> option, LARGE_ANON_FOLIO, which defaults to disabled and can only be >> enabled if the architecture has declared its support. When disabled, it >> forces the max order values, LARGE_ANON_FOLIO_NOTHP_ORDER_MAX and >> LARGE_ANON_FOLIO_THP_ORDER_MAX to 0, meaning only a single page is ever >> allocated. >> >> Signed-off-by: Ryan Roberts >> --- >> mm/Kconfig | 39 +++++++++++++++++++++++++++++++++++++++ >> mm/memory.c | 8 ++++++++ >> 2 files changed, 47 insertions(+) >> >> diff --git a/mm/Kconfig b/mm/Kconfig >> index 7672a22647b4..f4ba48c37b75 100644 >> --- a/mm/Kconfig >> +++ b/mm/Kconfig >> @@ -1208,4 +1208,43 @@ config PER_VMA_LOCK >> >> source "mm/damon/Kconfig" >> >> +config ARCH_SUPPORTS_LARGE_ANON_FOLIO >> + def_bool n >> + help >> + An arch should select this symbol if wants to allow LARGE_ANON_FOLIO >> + to be enabled. It must also set the following integer values: >> + - ARCH_LARGE_ANON_FOLIO_NOTHP_ORDER_MAX >> + - ARCH_LARGE_ANON_FOLIO_THP_ORDER_MAX >> + >> +config ARCH_LARGE_ANON_FOLIO_NOTHP_ORDER_MAX >> + int >> + help >> + The maximum size of folio to allocate for an anonymous VMA PTE-mapping >> + that does not have the MADV_HUGEPAGE hint set. >> + >> +config ARCH_LARGE_ANON_FOLIO_THP_ORDER_MAX >> + int >> + help >> + The maximum size of folio to allocate for an anonymous VMA PTE-mapping >> + that has the MADV_HUGEPAGE hint set. >> + >> +config LARGE_ANON_FOLIO >> + bool "Allocate large folios for anonymous memory" >> + depends on ARCH_SUPPORTS_LARGE_ANON_FOLIO >> + default n >> + help >> + Use large (bigger than order-0) folios to back anonymous memory where >> + possible. This reduces the number of page faults, as well as other >> + per-page overheads to improve performance for many workloads. >> + >> +config LARGE_ANON_FOLIO_NOTHP_ORDER_MAX >> + int >> + default 0 if !LARGE_ANON_FOLIO >> + default ARCH_LARGE_ANON_FOLIO_NOTHP_ORDER_MAX >> + >> +config LARGE_ANON_FOLIO_THP_ORDER_MAX >> + int >> + default 0 if !LARGE_ANON_FOLIO >> + default ARCH_LARGE_ANON_FOLIO_THP_ORDER_MAX >> + >> endmenu > > I don't think an MVP should add this many Kconfigs. One Kconfig sounds > reasonable to me for now. If we move to arch_wants_pte_order() as you suggested (in your response to patch 3) then I agree we can remove most of these. I still think we might want 2 though. For an arch that does not implement arch_wants_pte_order() we wouldn't want LARGE_ANON_FOLIO to show up in menuconfig so we would still need ARCH_SUPPORTS_LARGE_ANON_FOLIO: config ARCH_SUPPORTS_LARGE_ANON_FOLIO def_bool n help An arch should select this symbol if wants to allow LARGE_ANON_FOLIO to be enabled. In this case, It must also define arch_wants_pte_order() config LARGE_ANON_FOLIO bool "Allocate large folios for anonymous memory" depends on ARCH_SUPPORTS_LARGE_ANON_FOLIO default n help Use large (bigger than order-0) folios to back anonymous memory where possible. This reduces the number of page faults, as well as other per-page overheads to improve performance for many workloads. What do you think?