linux-kernel - Re: [RFC PATCH] mm/rmap: do not call mmu_notifier_invalidate

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Date:   Tue, 29 Aug 2017 12:16:49 -0700
From:   Linus Torvalds <torvalds@...ux-foundation.org>
To:     Jérôme Glisse <jglisse@...hat.com>
Cc:     Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        linux-mm <linux-mm@...ck.org>, Bernhard Held <berny156@....de>,
        Adam Borowski <kilobyte@...band.pl>,
        Andrea Arcangeli <aarcange@...hat.com>,
        Radim Krčmář <rkrcmar@...hat.com>,
        Wanpeng Li <kernellwp@...il.com>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Takashi Iwai <tiwai@...e.de>,
        Nadav Amit <nadav.amit@...il.com>,
        Mike Galbraith <efault@....de>,
        "Kirill A . Shutemov" <kirill.shutemov@...ux.intel.com>,
        axie <axie@....com>, Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [RFC PATCH] mm/rmap: do not call mmu_notifier_invalidate_page() v3

On Tue, Aug 29, 2017 at 12:09 PM, Linus Torvalds
<torvalds@...ux-foundation.org> wrote:
>
> So any approach like this is fundamentally garbage. Really. Stop
> sending crap. This is exactly tehe same thing that we already reverted
> because it was broken shit. Why do you re-send it without actually
> fixing the fundamental problems that were pointed out?

Here's what I think might work:

 - put mmu_notifier_invalidate_range_start() before the rmap lock is
taken (and yes, this means that you don't know if it actually will do
anyhting)

 - put mmu_notifier_invalidate_range_end() after the lock is released.
And yes, this means that it will be unconditional and regardless of
whether anything happened)

And then you can check if something actually happened by catching the
*ATOMIC* call to mmu_notifier_invalidate_page(), setting a flag, and
then doing something blocking at mmu_notifier_invalidate_range_end()
time.

Maybe.

I don't know what the KVM issues are.

                Linus