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From: Andy Lutomirski <luto@amacapital.net>
Date: Wed, 9 Mar 2016 22:45:33 -0800
Message-ID: <CALCETrUijqLwS98M_EnW5OH=CSv_SwjKGC5FkAxFEcWiq0RM2A@mail.gmail.com>
Subject: Re: [PATCH 03/11] x86/mm/hotplug: Don't remove PGD entries in remove_pagetable()
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To: Ingo Molnar <mingo@kernel.org>
Cc: "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>, "linux-mm@kvack.org" <linux-mm@kvack.org>, Andrew Morton <akpm@linux-foundation.org>, Denys Vlasenko <dvlasenk@redhat.com>, Brian Gerst <brgerst@gmail.com>, Peter Zijlstra <peterz@infradead.org>, Borislav Petkov <bp@alien8.de>, "H. Peter Anvin" <hpa@zytor.com>, Linus Torvalds <torvalds@linux-foundation.org>, Oleg Nesterov <oleg@redhat.com>, Waiman Long <waiman.long@hp.com>, Thomas Gleixner <tglx@linutronix.de>

On Fri, Feb 12, 2016 at 11:04 AM, Andy Lutomirski <luto@amacapital.net> wrote:
> On Mon, Sep 21, 2015 at 11:23 PM, Ingo Molnar <mingo@kernel.org> wrote:
>> So when memory hotplug removes a piece of physical memory from pagetable
>> mappings, it also frees the underlying PGD entry.
>>
>> This complicates PGD management, so don't do this. We can keep the
>> PGD mapped and the PUD table all clear - it's only a single 4K page
>> per 512 GB of memory hotplugged.
>
> Ressurecting an ancient thread: I want this particular change to make
> it (much) easier to make vmapped stacks work correctly.  Could it be
> applied by itself?
>

It's incomplete.  pageattr.c has another instance of the same thing.
I'll see if I can make it work, but I may end up doing something a
little different.

--Andy

-- 
Andy Lutomirski
AMA Capital Management, LLC

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