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From: Andy Lutomirski <luto@kernel.org>
Date: Wed, 12 Jul 2017 16:36:13 -0700
Message-ID: <CALCETrXr16TGe1gxnPajqpq-G8z1hK_fzPzZiJa+h+zZ8RysNw@mail.gmail.com>
Subject: Re: Potential race in TLB flush batching?
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Sender: owner-linux-mm@kvack.org
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To: Nadav Amit <nadav.amit@gmail.com>
Cc: Mel Gorman <mgorman@suse.de>, Andy Lutomirski <luto@kernel.org>, "open list:MEMORY MANAGEMENT" <linux-mm@kvack.org>

On Wed, Jul 12, 2017 at 4:27 PM, Nadav Amit <nadav.amit@gmail.com> wrote:
>
> Actually, I think that based on Andy=E2=80=99s patches there is a relativ=
ely
> reasonable solution. For each mm we will hold both a =E2=80=9Cpending_tlb=
_gen=E2=80=9D
> (increased under the PT-lock) and an =E2=80=9Cexecuted_tlb_gen=E2=80=9D. =
Once
> flush_tlb_mm_range finishes flushing it will use cmpxchg to update the
> executed_tlb_gen to the pending_tlb_gen that was prior the flush (the
> cmpxchg will ensure the TLB gen only goes forward). Then, whenever
> pending_tlb_gen is different than executed_tlb_gen - a flush is needed.
>

Why do we need executed_tlb_gen?  We already have
cpu_tlbstate.ctxs[...].tlb_gen.  Or is the idea that executed_tlb_gen
guarantees that all cpus in mm_cpumask are at least up to date to
executed_tlb_gen?

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