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 70A12C10F05 for ; Wed, 6 Dec 2023 14:22:53 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1378900AbjLFOWp (ORCPT ); Wed, 6 Dec 2023 09:22:45 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:33902 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1378736AbjLFOWn (ORCPT ); Wed, 6 Dec 2023 09:22:43 -0500 Received: from foss.arm.com (foss.arm.com [217.140.110.172]) by lindbergh.monkeyblade.net (Postfix) with ESMTP id 46437D44 for ; Wed, 6 Dec 2023 06:22:49 -0800 (PST) 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 EBF6A1474; Wed, 6 Dec 2023 06:23:34 -0800 (PST) Received: from [10.57.73.130] (unknown [10.57.73.130]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id D7DE33F5A1; Wed, 6 Dec 2023 06:22:45 -0800 (PST) Message-ID: <7a18b924-1012-4649-9289-ab5075eb7736@arm.com> Date: Wed, 6 Dec 2023 14:22:44 +0000 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v8 00/10] Multi-size THP for anonymous memory Content-Language: en-GB To: David Hildenbrand , Andrew Morton , Matthew Wilcox , Yin Fengwei , Yu Zhao , Catalin Marinas , Anshuman Khandual , Yang Shi , "Huang, Ying" , Zi Yan , Luis Chamberlain , Itaru Kitayama , "Kirill A. Shutemov" , John Hubbard , David Rientjes , Vlastimil Babka , Hugh Dickins , Kefeng Wang , Barry Song <21cnbao@gmail.com>, Alistair Popple Cc: linux-mm@kvack.org, linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org References: <20231204102027.57185-1-ryan.roberts@arm.com> <8d5fdb17-c670-4814-8f48-4b90062668fc@redhat.com> <7d3457cd-5e3d-42a7-8113-545da646d7c8@redhat.com> From: Ryan Roberts In-Reply-To: <7d3457cd-5e3d-42a7-8113-545da646d7c8@redhat.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 06/12/2023 10:22, David Hildenbrand wrote: > On 06.12.23 11:13, Ryan Roberts wrote: >> On 05/12/2023 17:21, David Hildenbrand wrote: >>> On 04.12.23 11:20, Ryan Roberts wrote: >>>> Hi All, >>>> >>>> A new week, a new version, a new name... This is v8 of a series to implement >>>> multi-size THP (mTHP) for anonymous memory (previously called "small-sized THP" >>>> and "large anonymous folios"). Matthew objected to "small huge" so hopefully >>>> this fares better. >>>> >>>> The objective of this is to improve performance by allocating larger chunks of >>>> memory during anonymous page faults: >>>> >>>> 1) Since SW (the kernel) is dealing with larger chunks of memory than base >>>>      pages, there are efficiency savings to be had; fewer page faults, >>>> batched PTE >>>>      and RMAP manipulation, reduced lru list, etc. In short, we reduce kernel >>>>      overhead. This should benefit all architectures. >>>> 2) Since we are now mapping physically contiguous chunks of memory, we can take >>>>      advantage of HW TLB compression techniques. A reduction in TLB pressure >>>>      speeds up kernel and user space. arm64 systems have 2 mechanisms to >>>> coalesce >>>>      TLB entries; "the contiguous bit" (architectural) and HPA (uarch). >>>> >>>> This version changes the name and tidies up some of the kernel code and test >>>> code, based on feedback against v7 (see change log for details). >>>> >>>> By default, the existing behaviour (and performance) is maintained. The user >>>> must explicitly enable multi-size THP to see the performance benefit. This is >>>> done via a new sysfs interface (as recommended by David Hildenbrand - thanks to >>>> David for the suggestion)! This interface is inspired by the existing >>>> per-hugepage-size sysfs interface used by hugetlb, provides full backwards >>>> compatibility with the existing PMD-size THP interface, and provides a base for >>>> future extensibility. See [8] for detailed discussion of the interface. >>>> >>>> This series is based on mm-unstable (715b67adf4c8). >>> >>> I took a look at the core pieces. Some things might want some smaller tweaks, >>> but nothing that should stop this from having fun in mm-unstable, and replacing >>> the smaller things as we move forward. >>> >> >> Thanks! I'll address your comments and see if I can post another (final??) >> version next week. > > It's always possible to do incremental changes on top that Andrew will squash in > the end. I even recall that he prefers that way once a series has been in > mm-unstable for a bit, so one can better observe the diff and which effects they > have. > I've responded to all your comments. There are a bunch of changes that I agree would be good to make (and some which I disagree with - would be good if you get a chance to respond). I think I can get all the changes done and tested by Friday. So perhaps it's simplest to keep this out of mm-unstable until then, and put the new version in on Friday? Then if there are any more small changes to do, I can do those as diffs? Thanks, Ryan