linux-kernel - Re: [PATCH 08/12] x86/mm: Remove pgd_list use from vmalloc_sync

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Message-ID: <CALCETrXZwiv=kjPE0LKZE2Z42+R+De-brRM02HgZGnxtur1G_A@mail.gmail.com>
Date:	Thu, 11 Jun 2015 08:04:23 -0700
From:	Andy Lutomirski <luto@...capital.net>
To:	Ingo Molnar <mingo@...nel.org>
Cc:	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	linux-mml@...r.kernel.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>,
	Thomas Gleixner <tglx@...utronix.de>,
	Waiman Long <Waiman.Long@...com>
Subject: Re: [PATCH 08/12] x86/mm: Remove pgd_list use from vmalloc_sync_all()

On Thu, Jun 11, 2015 at 7:07 AM, Ingo Molnar <mingo@...nel.org> wrote:
> The vmalloc() code uses vmalloc_sync_all() to synchronize changes to
> the global reference kernel PGD to task PGDs.

Does it?  AFAICS the only caller is register_die_notifier, and it's
not really clear to me why that exists.

At some point I'd love to remove lazy kernel PGD sync from the kernel
entirely (or at least from x86) and just do it when we switch mms.
Now that you're removing all code that deletes kernel PGD entries, I
think all we'd need to do is to add a per-PGD or per-mm count of the
number of kernel entries populated and to fix it up when we switch to
an mm with fewer entries populated than init_mm.

--Andy
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