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

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Message-ID: <CALCETrXV34q4ViE46sHN6QxucmxoBYN0xKz4p7H9Cr=7VpwQUA@mail.gmail.com>
Date:	Fri, 12 Feb 2016 11:04:57 -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 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?

--Andy