From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-ed1-f69.google.com (mail-ed1-f69.google.com [209.85.208.69]) by kanga.kvack.org (Postfix) with ESMTP id 814736B0006 for ; Tue, 16 Oct 2018 07:30:02 -0400 (EDT) Received: by mail-ed1-f69.google.com with SMTP id e5-v6so13941768eda.4 for ; Tue, 16 Oct 2018 04:30:02 -0700 (PDT) Received: from mx1.suse.de (mx2.suse.de. [195.135.220.15]) by mx.google.com with ESMTPS id z22-v6si3192788ejm.80.2018.10.16.04.30.00 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Tue, 16 Oct 2018 04:30:01 -0700 (PDT) Subject: Re: [PATCH 2/4] mm: speed up mremap by 500x on large regions (v2) References: <20181013013200.206928-1-joel@joelfernandes.org> <20181013013200.206928-3-joel@joelfernandes.org> <20181015094209.GA31999@infradead.org> <20181015223303.GA164293@joelaf.mtv.corp.google.com> From: Vlastimil Babka Message-ID: <35b9c85a-b366-9ca3-5647-c2568c811961@suse.cz> Date: Tue, 16 Oct 2018 13:29:52 +0200 MIME-Version: 1.0 In-Reply-To: <20181015223303.GA164293@joelaf.mtv.corp.google.com> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org List-ID: To: Joel Fernandes , Christoph Hellwig Cc: linux-kernel@vger.kernel.org, linux-mips@linux-mips.org, Rich Felker , linux-ia64@vger.kernel.org, linux-sh@vger.kernel.org, Peter Zijlstra , Catalin Marinas , Dave Hansen , Will Deacon , mhocko@kernel.org, linux-mm@kvack.org, lokeshgidra@google.com, linux-riscv@lists.infradead.org, elfring@users.sourceforge.net, Jonas Bonn , kvmarm@lists.cs.columbia.edu, dancol@google.com, Yoshinori Sato , sparclinux@vger.kernel.org, linux-xtensa@linux-xtensa.org, linux-hexagon@vger.kernel.org, Helge Deller , "maintainer:X86 ARCHITECTURE 32-BIT AND 64-BIT" , hughd@google.com, "James E.J. Bottomley" , kasan-dev@googlegroups.com, anton.ivanov@kot-begemot.co.uk, Ingo Molnar , Geert Uytterhoeven , Andrey Ryabinin , linux-snps-arc@lists.infradead.org, kernel-team@android.com, Sam Creasey , Fenghua Yu , linux-s390@vger.kernel.org, Jeff Dike , linux-um@lists.infradead.org, Stefan Kristiansson , Julia Lawall , linux-m68k@lists.linux-m68k.org, Borislav Petkov , Andy Lutomirski , nios2-dev@lists.rocketboards.org, kirill@shutemov.name, Stafford Horne , Guan Xuetao , Chris Zankel , Tony Luck , Richard Weinberger , linux-parisc@vger.kernel.org, pantin@google.com, Max Filippov , minchan@kernel.org, Thomas Gleixner , linux-alpha@vger.kernel.org, Ley Foon Tan , akpm@linux-foundation.org, linuxppc-dev@lists.ozlabs.org, "David S. Miller" On 10/16/18 12:33 AM, Joel Fernandes wrote: > On Mon, Oct 15, 2018 at 02:42:09AM -0700, Christoph Hellwig wrote: >> On Fri, Oct 12, 2018 at 06:31:58PM -0700, Joel Fernandes (Google) wrote: >>> Android needs to mremap large regions of memory during memory management >>> related operations. >> >> Just curious: why? > > In Android we have a requirement of moving a large (up to a GB now, but may > grow bigger in future) memory range from one location to another. I think Christoph's "why?" was about the requirement, not why it hurts applications. I admit I'm now also curious :) > This move > operation has to happen when the application threads are paused for this > operation. Therefore, an inefficient move like it is now (for example 250ms > on arm64) will cause response time issues for applications, which is not > acceptable. Huge pages cannot be used in such memory ranges to avoid this > inefficiency as (when the application threads are running) our fault handlers > are designed to process 4KB pages at a time, to keep response times low. So > using huge pages in this context can, again, cause response time issues. > > Also, the mremap syscall waiting for quarter of a second for a large mremap > is quite weird and we ought to improve it where possible.