linux-kernel - Re: [PATCH 26/26] x86/mm: allow to have userspace mappings above 47-bits

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Message-ID: <20170324090307.hcx57t6yr4wqv4uz@node.shutemov.name>
Date:   Fri, 24 Mar 2017 12:03:07 +0300
From:   "Kirill A. Shutemov" <kirill@...temov.name>
To:     "Aneesh Kumar K.V" <aneesh.kumar@...ux.vnet.ibm.com>
Cc:     "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Andrew Morton <akpm@...ux-foundation.org>, x86@...nel.org,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Arnd Bergmann <arnd@...db.de>,
        "H. Peter Anvin" <hpa@...or.com>, Andi Kleen <ak@...ux.intel.com>,
        Dave Hansen <dave.hansen@...el.com>,
        Andy Lutomirski <luto@...capital.net>,
        Michal Hocko <mhocko@...e.com>, linux-arch@...r.kernel.org,
        linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 26/26] x86/mm: allow to have userspace mappings above
 47-bits

On Sun, Mar 19, 2017 at 02:25:08PM +0530, Aneesh Kumar K.V wrote:
> >>> So if I have done a successful mmap which returned > 128TB what should a
> >>> following mmap(0,...) return ? Should that now search the *full* address
> >>> space or below 128TB ?
> >>
> >> No, I don't think so. And this implementation doesn't do this.
> >>
> >> It's safer this way: if an library can't handle high addresses, it's
> >> better not to switch it automagically to full address space if other part
> >> of the process requested high address.
> >>
> >
> > What is the epectation when the hint addr is below 128TB but addr + len >
> > 128TB ? Should such mmap request fail ?
> 
> Considering that we have stack at the top (around 128TB) we may not be
> able to get a free area for such a request. But I guess the idea here is
> that if hint address is below 128TB, we behave as though our TASK_SIZE
> is 128TB ? Is that correct ?

Right.

-- 
 Kirill A. Shutemov