From mboxrd@z Thu Jan 1 00:00:00 1970 Received: with ECARTIS (v1.0.0; list linux-mips); Sun, 28 Oct 2018 23:40:23 +0100 (CET) Received: from mail-pg1-x541.google.com ([IPv6:2607:f8b0:4864:20::541]:37670 "EHLO mail-pg1-x541.google.com" rhost-flags-OK-OK-OK-OK) by eddie.linux-mips.org with ESMTP id S23990392AbeJ1WkOL1YoB (ORCPT ); Sun, 28 Oct 2018 23:40:14 +0100 Received: by mail-pg1-x541.google.com with SMTP id c10-v6so2938617pgq.4 for ; Sun, 28 Oct 2018 15:40:14 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20161025; h=date:from:to:cc:subject:message-id:references:mime-version :content-disposition:in-reply-to:user-agent; bh=GFtksEV3l5eq+mnfMA1OwOjA0oBp/IcRdRQ8wGi247I=; b=hzlz7jFWANzmnQYBfUjAY47ntJv9ruGodd92q7E4yeWjWXy4EZl6bPRcEO0kKVxcET 8l/LxbyoIEOMIv2Qws7VhhdBdB2WSqhVRO2xFO6BoL6UVCnvmAbklAgUnFIPczbls2XR 8t+tWl9FODh8azBtSJSVtOJ8ASXQGH4rOt//srkRKwJB3n5TPhA7eLFTkuIKOx//Tn6i wCdbM58gxJCZ3Wya+Xx9knz+xP1bKelI2gOlUgbKzh9xt2GwpzMnGwoSI1DVJtDgp4Fn d+gXcEV0Ha0CDx7RrL2gR1D2FtTk3tSVbj1J8r71HdedlxSopPgWOCsGk19JAS3kF9ps MWOA== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:date:from:to:cc:subject:message-id:references :mime-version:content-disposition:in-reply-to:user-agent; bh=GFtksEV3l5eq+mnfMA1OwOjA0oBp/IcRdRQ8wGi247I=; b=f4YmYf4ystAX2N6OCCYwRGuc71NsmBOVpaWTsnYSkBP8SkTJIgcjhcA0pp+ZB8WOSu 9b9SzV1Yv4qw4aWC96py+V+kgto35U7t3m5thTKAFPrL/XmmOw/wnelzC60sPpdvDPiR U+jbh9aJw9uU6JmLFvN0q/Gtf6YOG4bNBRjp0TYyHpEAqCvP8xt8TFs7Uu23WkCfiKUI 5ra9yV2OiigcJun6x5hAU3f4IDurHxLrCk8QVrn+rD4HMLOl3gp6pQwqMXvlSvmenE4C Oc4BLVU8r6Q2H+DqQ9rAzCz5TJfB5jvVZISNJJRdD6Yrb46YojlTA5zT5NJBICkCY426 fWlQ== X-Gm-Message-State: AGRZ1gJjcRG4YCtczK3yd7Ad5LVbgCLZ+uzvBkZaYfDdUqPwg6qy9tK6 MXn9OgtJuTDbiBGUUa3aPH8= X-Google-Smtp-Source: AJdET5fu0DqTEYAGDBSaxsVyd0K3i3CEEiTSqETAuxd4rlFGA5L/e1X97o5DIUSGPTfJJWdGWN6dQw== X-Received: by 2002:a63:181:: with SMTP id 123-v6mr11570471pgb.149.1540766407194; Sun, 28 Oct 2018 15:40:07 -0700 (PDT) Received: from localhost (14-202-194-140.static.tpgi.com.au. [14.202.194.140]) by smtp.gmail.com with ESMTPSA id t4-v6sm19146464pfb.44.2018.10.28.15.40.05 (version=TLS1_2 cipher=ECDHE-RSA-CHACHA20-POLY1305 bits=256/256); Sun, 28 Oct 2018 15:40:05 -0700 (PDT) Date: Mon, 29 Oct 2018 09:40:02 +1100 From: Balbir Singh To: Joel Fernandes Cc: "Kirill A. Shutemov" , linux-kernel@vger.kernel.org, kernel-team@android.com, minchan@kernel.org, pantin@google.com, hughd@google.com, lokeshgidra@google.com, dancol@google.com, mhocko@kernel.org, akpm@linux-foundation.org, Andrey Ryabinin , Andy Lutomirski , anton.ivanov@kot-begemot.co.uk, Borislav Petkov , Catalin Marinas , Chris Zankel , Dave Hansen , "David S. Miller" , elfring@users.sourceforge.net, Fenghua Yu , Geert Uytterhoeven , Guan Xuetao , Helge Deller , Ingo Molnar , "James E.J. Bottomley" , Jeff Dike , Jonas Bonn , Julia Lawall , kasan-dev@googlegroups.com, kvmarm@lists.cs.columbia.edu, Ley Foon Tan , linux-alpha@vger.kernel.org, linux-hexagon@vger.kernel.org, linux-ia64@vger.kernel.org, linux-m68k@lists.linux-m68k.org, linux-mips@linux-mips.org, linux-mm@kvack.org, linux-parisc@vger.kernel.org, linuxppc-dev@lists.ozlabs.org, linux-riscv@lists.infradead.org, linux-s390@vger.kernel.org, linux-sh@vger.kernel.org, linux-snps-arc@lists.infradead.org, linux-um@lists.infradead.org, linux-xtensa@linux-xtensa.org, Max Filippov , nios2-dev@lists.rocketboards.org, Peter Zijlstra , Richard Weinberger , Rich Felker , Sam Creasey , sparclinux@vger.kernel.org, Stafford Horne , Stefan Kristiansson , Thomas Gleixner , Tony Luck , Will Deacon , "maintainer:X86 ARCHITECTURE (32-BIT AND 64-BIT)" , Yoshinori Sato Subject: Re: [PATCH 2/4] mm: speed up mremap by 500x on large regions (v2) Message-ID: <20181028224002.GA16399@350D> References: <20181013013200.206928-1-joel@joelfernandes.org> <20181013013200.206928-3-joel@joelfernandes.org> <20181024101255.it4lptrjogalxbey@kshutemo-mobl1> <20181024115733.GN8537@350D> <20181025021350.GB13560@joelaf.mtv.corp.google.com> <20181027102102.GO8537@350D> <20181027193917.GA51131@joelaf.mtv.corp.google.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20181027193917.GA51131@joelaf.mtv.corp.google.com> User-Agent: Mutt/1.9.4 (2018-02-28) Return-Path: X-Envelope-To: <"|/home/ecartis/ecartis -s linux-mips"> (uid 0) X-Orcpt: rfc822;linux-mips@linux-mips.org Original-Recipient: rfc822;linux-mips@linux-mips.org X-archive-position: 66966 X-ecartis-version: Ecartis v1.0.0 Sender: linux-mips-bounce@linux-mips.org Errors-to: linux-mips-bounce@linux-mips.org X-original-sender: bsingharora@gmail.com Precedence: bulk List-help: List-unsubscribe: List-software: Ecartis version 1.0.0 List-Id: linux-mips X-List-ID: linux-mips List-subscribe: List-owner: List-post: List-archive: X-list: linux-mips On Sat, Oct 27, 2018 at 12:39:17PM -0700, Joel Fernandes wrote: > Hi Balbir, > > On Sat, Oct 27, 2018 at 09:21:02PM +1100, Balbir Singh wrote: > > On Wed, Oct 24, 2018 at 07:13:50PM -0700, Joel Fernandes wrote: > > > On Wed, Oct 24, 2018 at 10:57:33PM +1100, Balbir Singh wrote: > > > [...] > > > > > > + pmd_t pmd; > > > > > > + > > > > > > + new_ptl = pmd_lockptr(mm, new_pmd); > > > > > > > > > > > > Looks like this is largely inspired by move_huge_pmd(), I guess a lot of > > > > the code applies, why not just reuse as much as possible? The same comments > > > > w.r.t mmap_sem helping protect against lock order issues applies as well. > > > > > > I thought about this and when I looked into it, it seemed there are subtle > > > differences that make such sharing not worth it (or not possible). > > > > > > > Could you elaborate on them? > > The move_huge_page function is defined only for CONFIG_TRANSPARENT_HUGEPAGE > so we cannot reuse it to begin with, since we have it disabled on our > systems. I am not sure if it is a good idea to split that out and refactor it > for reuse especially since our case is quite simple compared to huge pages. > > There are also a couple of subtle differences between the move_normal_pmd and > the move_huge_pmd. Atleast 2 of them are: > > 1. We don't concern ourself with the PMD dirty bit, since the pages being > moved are normal pages and at the soft-dirty bit accounting is at the PTE > level, since we are not moving PTEs, we don't need to do that. > > 2. The locking is simpler as Kirill pointed, pmd_lock cannot fail however > __pmd_trans_huge_lock can. > > I feel it is not super useful to refactor move_huge_pmd to support our case > especially since move_normal_pmd is quite small, so IMHO the benefit of code > reuse isn't there very much. > My big concern is that any bug fixes will need to monitor both paths. Do you see a big overhead in checking the soft dirty bit? The locking is a little different. Having said that, I am not strictly opposed to the extra code, just concerned about missing fixes/updates as we find them. > Do let me know your thoughts and thanks for your interest in this. > > Balbir Singh.