linux-kernel - Re: [PATCH 2/8] x86: use exit_lazy_tlb rather than membarrier_mm_sync_core_before

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Date:   Mon, 14 Dec 2020 15:53:40 +1000
From:   Nicholas Piggin <npiggin@...il.com>
To:     Andy Lutomirski <luto@...nel.org>
Cc:     Anton Blanchard <anton@...abs.org>, Arnd Bergmann <arnd@...db.de>,
        linux-arch <linux-arch@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Linux-MM <linux-mm@...ck.org>,
        linuxppc-dev <linuxppc-dev@...ts.ozlabs.org>,
        Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
        Peter Zijlstra <peterz@...radead.org>, X86 ML <x86@...nel.org>
Subject: Re: [PATCH 2/8] x86: use exit_lazy_tlb rather than
 membarrier_mm_sync_core_before_usermode

Excerpts from Nicholas Piggin's message of December 14, 2020 2:07 pm:
> Excerpts from Andy Lutomirski's message of December 11, 2020 10:11 am:
>>> On Dec 5, 2020, at 7:59 PM, Nicholas Piggin <npiggin@...il.com> wrote:
>>>
>> 
>>> I'm still going to persue shoot-lazies for the merge window. As you
>>> see it's about a dozen lines and a if (IS_ENABLED(... in core code.
>>> Your change is common code, but a significant complexity (which
>>> affects all archs) so needs a lot more review and testing at this
>>> point.
>> 
>> I don't think it's ready for this merge window.
> 
> Yes next one I meant (aka this one for development perspective :)).
> 
>> I read the early
>> patches again, and I think they make the membarrier code worse, not
>> better.
> 
> Mathieu and I disagree, so we are at an impasse.

Well actually not really, I went and cut out the exit_lazy_tlb stuff
from the patch series, those are better to be untangled anyway. I think 
an earlier version had something in exit_lazy_tlb for the mm refcounting 
change but it's not required now anyway.

I'll split them out and just work on the shoot lazies series for now, I
might revisit exit_lazy_tlb after the dust settles from that and the
current membarrier changes. I'll test and repost shortly.

Thanks,
Nick