linux-kernel - Re: [PATCH 03/11] x86/mm/hotplug: Don't remove PGD entries in remove

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Message-ID: <CALCETrUijqLwS98M_EnW5OH=CSv_SwjKGC5FkAxFEcWiq0RM2A@mail.gmail.com>
Date:	Wed, 9 Mar 2016 22:45:33 -0800
From:	Andy Lutomirski <luto@...capital.net>
To:	Ingo Molnar <mingo@...nel.org>
Cc:	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-mm@...ck.org" <linux-mm@...ck.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Denys Vlasenko <dvlasenk@...hat.com>,
	Brian Gerst <brgerst@...il.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Borislav Petkov <bp@...en8.de>,
	"H. Peter Anvin" <hpa@...or.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Oleg Nesterov <oleg@...hat.com>,
	Waiman Long <waiman.long@...com>,
	Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [PATCH 03/11] x86/mm/hotplug: Don't remove PGD entries in remove_pagetable()

On Fri, Feb 12, 2016 at 11:04 AM, Andy Lutomirski <luto@...capital.net> wrote:
> On Mon, Sep 21, 2015 at 11:23 PM, Ingo Molnar <mingo@...nel.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