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Subject: Re: [PATCH 07/13] powerpc: Preemptible mmu_gather
From: Peter Zijlstra <peterz@infradead.org>
To: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Cc: Andrea Arcangeli <aarcange@redhat.com>, Avi Kivity <avi@redhat.com>,
       Thomas Gleixner <tglx@linutronix.de>, Rik van Riel <riel@redhat.com>,
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       Linus Torvalds <torvalds@linux-foundation.org>,
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       David Miller <davem@davemloft.net>,
       Hugh Dickins <hugh.dickins@tiscali.co.uk>, Mel Gorman <mel@csn.ul.ie>,
       Nick Piggin <npiggin@suse.de>
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Date: Tue, 13 Apr 2010 12:22:23 +0200
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On Tue, 2010-04-13 at 11:23 +1000, Benjamin Herrenschmidt wrote:
> >  static inline void arch_leave_lazy_mmu_mode(void)
> >  {
> > -     struct ppc64_tlb_batch *batch = &__get_cpu_var(ppc64_tlb_batch);
> > +     struct ppc64_tlb_batch *batch = &get_cpu_var(ppc64_tlb_batch);
> > +
> > +     if (batch->active) {
> > +             if (batch->index)
> > +                     __flush_tlb_pending(batch);
> > +             batch->active = 0;
> > +     }
> 
> Can index be > 0 if active == 0 ? I though not, which means you don't
> need to add a test on active, do you ?

True I guess, but like this we avoid a write, doesn't really matter I
suspect.

> I'm also pondering whether we should just stick something in the
> task/thread struct and avoid that whole per-cpu manipulation including
> the stuff in process.c in fact.

Can do, I can add batching similar to the generic code to the
thread_info thingy.

> Heh, maybe it's time to introduce thread vars ? :-) 

Heh, that seems like a real good way to waste a lot of memory fast ;-)