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

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Date:	Thu, 10 Mar 2016 10:56:01 +0100
From:	Ingo Molnar <mingo@...nel.org>
To:	Andy Lutomirski <luto@...capital.net>
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()


* Andy Lutomirski <luto@...capital.net> wrote:

> 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.

If so then mind picking up (and fixing ;-) tip:WIP.x86/mm in its entirety? It's 
well tested so shouldn't have too many easy to hit bugs. Feel free to rebase and 
restructure it, it's a WIP tree.

I keep getting distracted with other things but I'd hate if this got dropped on 
the floor.

Thanks,

	Ingo