linux-kernel - Re: Question on the five-level page table support patches

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Message-ID: <20170424220158.z67cir7sjfyn4wdt@node.shutemov.name>
Date:   Tue, 25 Apr 2017 01:01:58 +0300
From:   "Kirill A. Shutemov" <kirill@...temov.name>
To:     John Paul Adrian Glaubitz <glaubitz@...sik.fu-berlin.de>
Cc:     "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
        linux-kernel@...r.kernel.org, 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
Subject: Re: Question on the five-level page table support patches

On Mon, Apr 24, 2017 at 10:37:40PM +0200, John Paul Adrian Glaubitz wrote:
> On 04/24/2017 06:19 PM, Kirill A. Shutemov wrote:
> > In proposed implementation, we also use hint address, but in different
> > way: by default, if hint address is NULL, kernel would not create mappings
> > above 47-bits, preserving compatibility.
> 
> Ooooh, that would solve a lot of problems actually if it were to be available
> on all architectures. On SPARC, the situation is really annoying and I have
> been discussing a solution with the Qt developers and they suggested a
> similar approach, just one that would also apply to brk() [1].
> 
> > If an application wants to have access to larger address space, it has to
> > specify hint addess above 47-bits.
> > 
> > See details here:
> > 
> > http://lkml.kernel.org/r/20170420162147.86517-10-kirill.shutemov@linux.intel.com
> 
> Thanks. I'll have a read. Although from your message I'm reading out that
> this particular proposal got rejected.

No. I just wasn't applied yet, so situation may change.

> Would be really nice to able to have a canonical solution for this issue,
> it's been biting us on SPARC for quite a while now due to the fact that
> virtual address space has been 52 bits on SPARC for a while now.

Power folks are going to implement similar approach. I don't see why Sparc
can't go the same route.

-- 
 Kirill A. Shutemov