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From: Andy Lutomirski <luto@amacapital.net>
Date: Tue, 16 Dec 2014 16:41:16 -0800
Message-ID: <CALCETrVLrXOZNY6Xha+TukJMTb2ni70FN==rL8KHM6FrMwWzVQ@mail.gmail.com>
Subject: Re: frequent lockups in 3.18rc4
To: Linus Torvalds <torvalds@linux-foundation.org>,
        Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
Cc: Peter Zijlstra <peterz@infradead.org>, Mel Gorman <mgorman@suse.de>,
        Thomas Gleixner <tglx@linutronix.de>,
        Steven Rostedt <rostedt@goodmis.org>, Tejun Heo <tj@kernel.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        Arnaldo Carvalho de Melo <acme@ghostprotocols.net>,
        Frederic Weisbecker <fweisbec@gmail.com>,
        Don Zickus <dzickus@redhat.com>, Dave Jones <davej@redhat.com>,
        "the arch/x86 maintainers" <x86@kernel.org>
Content-Type: text/plain; charset=UTF-8
Sender: linux-kernel-owner@vger.kernel.org

On Tue, Dec 16, 2014 at 4:00 PM, Linus Torvalds
<torvalds@linux-foundation.org> wrote:
> On Tue, Dec 16, 2014 at 3:02 PM, Peter Zijlstra <peterz@infradead.org> wrote:
>>
>> OK, should we just stick it in the x86 tree and see if anything
>> explodes? ;-)
>
> Gaah, I got confused about the patches.
>
> And something did explode, it showed some Xen nasties. Xen has that
> odd "we don't share PMD entries between MM's" thing going on, which
> means that the vmalloc fault thing does actually have to occasionally
> walk two levels rather than just copy the top level. I'm still not
> sure why Xen doesn't share PMD's, since threads that shame the MM
> clearly can share PMD's within Xen, but I gave up on it.

Sounds like it's time to ask Konrad, the source of all Xen understanding :)

Linus, do you have a pointer to whatever version of the patch you tried?

--Andy

>
> That said, making x86-64 use "read_cr3()" instead of
> "current->active_mm" would at least make things a bit safer wrt NMI's
> during the task switch, of course.  So *some* 32/64-bit consolidation
> should be done, but my patch went a bit too far for Xen.
>
>                       Linus


-- 
Andy Lutomirski
AMA Capital Management, LLC
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