linux-kernel - Re: [RFC, PATCHv2 29/29] mm, x86: introduce RLIMIT

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Date:   Thu, 5 Jan 2017 09:53:54 -0800
From:   Andy Lutomirski <luto@...capital.net>
To:     "Kirill A. Shutemov" <kirill@...temov.name>
Cc:     Arnd Bergmann <arnd@...db.de>,
        "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        X86 ML <x86@...nel.org>, Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>,
        "H. Peter Anvin" <hpa@...or.com>, Andi Kleen <ak@...ux.intel.com>,
        Dave Hansen <dave.hansen@...el.com>,
        linux-arch <linux-arch@...r.kernel.org>,
        "linux-mm@...ck.org" <linux-mm@...ck.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Linux API <linux-api@...r.kernel.org>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will.deacon@....com>
Subject: Re: [RFC, PATCHv2 29/29] mm, x86: introduce RLIMIT_VADDR

On Wed, Jan 4, 2017 at 6:19 AM, Kirill A. Shutemov <kirill@...temov.name> wrote:
> On Tue, Jan 03, 2017 at 10:27:22AM -0800, Andy Lutomirski wrote:
>> On Tue, Jan 3, 2017 at 8:04 AM, Kirill A. Shutemov <kirill@...temov.name> wrote:
>> > And what about stack? I'm not sure that everybody would be happy with
>> > stack in the middle of address space.
>>
>> I would, personally.  I think that, for very large address spaces, we
>> should allocate a large block of stack and get rid of the "stack grows
>> down forever" legacy idea.  Then we would never need to worry about
>> the stack eventually hitting some other allocation.  And 2^57 bytes is
>> hilariously large for a default stack.
>
> The stack in the middle of address space can prevent creating other huuuge
> contiguous mapping. Databases may want this.

Fair enough.  OTOH, 2^47 is nowhere near the middle if we were to put
it near the top of the legacy address space.