From mboxrd@z Thu Jan  1 00:00:00 1970
Return-Path: <linux-kernel-owner@vger.kernel.org>
Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand
        id S935135AbdBQVvA convert rfc822-to-8bit (ORCPT <rfc822;w@1wt.eu>);
        Fri, 17 Feb 2017 16:51:00 -0500
Received: from terminus.zytor.com ([65.50.211.136]:43624 "EHLO mail.zytor.com"
        rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP
        id S934415AbdBQVu6 (ORCPT <rfc822;linux-kernel@vger.kernel.org>);
        Fri, 17 Feb 2017 16:50:58 -0500
Date: Fri, 17 Feb 2017 13:50:32 -0800
User-Agent: K-9 Mail for Android
In-Reply-To: <CA+55aFzVWHUNuhTSBKLyLjOd4UQ8s1-RhMWA7oVr=3G5euo7ZQ@mail.gmail.com>
References: <20170217141328.164563-1-kirill.shutemov@linux.intel.com> <20170217141328.164563-34-kirill.shutemov@linux.intel.com> <CA+55aFwgbHxV-Ha2n1H=Z7P6bgcQ3D8aW=fr8ZrQ5OnvZ1vOYg@mail.gmail.com> <ae493a75-138c-9c01-d4a1-90bcd01d560f@intel.com> <CA+55aFzVWHUNuhTSBKLyLjOd4UQ8s1-RhMWA7oVr=3G5euo7ZQ@mail.gmail.com>
MIME-Version: 1.0
Content-Type: text/plain;
 charset=utf-8
Content-Transfer-Encoding: 8BIT
Subject: Re: [PATCHv3 33/33] mm, x86: introduce PR_SET_MAX_VADDR and PR_GET_MAX_VADDR
To: Linus Torvalds <torvalds@linux-foundation.org>,
        Dave Hansen <dave.hansen@intel.com>
CC: "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        the arch/x86 maintainers <x86@kernel.org>,
        Thomas Gleixner <tglx@linutronix.de>, Ingo Molnar <mingo@redhat.com>,
        Arnd Bergmann <arnd@arndb.de>, Andi Kleen <ak@linux.intel.com>,
        Andy Lutomirski <luto@amacapital.net>,
        "linux-arch@vger.kernel.org" <linux-arch@vger.kernel.org>,
        linux-mm <linux-mm@kvack.org>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        Catalin Marinas <catalin.marinas@arm.com>,
        Linux API <linux-api@vger.kernel.org>
From: hpa@zytor.com
Message-ID: <31716333-7B8E-4D70-815F-6AABBFBA1A00@zytor.com>
Sender: linux-kernel-owner@vger.kernel.org
List-ID: <linux-kernel.vger.kernel.org>
X-Mailing-List: linux-kernel@vger.kernel.org

On February 17, 2017 1:10:27 PM PST, Linus Torvalds <torvalds@linux-foundation.org> wrote:
>On Fri, Feb 17, 2017 at 1:04 PM, Dave Hansen <dave.hansen@intel.com>
>wrote:
>>
>> Is this likely to break anything in practice?  Nah.  But it would
>nice
>> to avoid it.
>
>So I go the other way: what *I* would like to avoid is odd code that
>is hard to follow. I'd much rather make the code be simple and the
>rules be straightforward, and not introduce that complicated
>"different address limits" thing at all.
>
>Then, _if_ we ever find a case where it makes a difference, we could
>go the more complex route. But not first implementation, and not
>without a real example of why we shouldn't just keep things simple.
>
>              Linus

However, we already have different address limits for different threads and/or syscall interfaces - 3 GiB (32-bit with legacy flag), 4 GiB (32-bit or x32), or 128 TiB... and for a while we had a 512 GiB option, too.  In that sense an address cap makes sense and generalizes what we already have.

It would be pretty hideous for the user, long term, to be artificially restricted to a legacy address cap unless they manage the address space themselves.
-- 
Sent from my Android device with K-9 Mail. Please excuse my brevity.