linux-kernel - Re: [PATCH 07/13] powerpc: Preemptible mmu

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Date:	Tue, 13 Apr 2010 12:22:23 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Benjamin Herrenschmidt <benh@...nel.crashing.org>
Cc:	Andrea Arcangeli <aarcange@...hat.com>,
	Avi Kivity <avi@...hat.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Rik van Riel <riel@...hat.com>, Ingo Molnar <mingo@...e.hu>,
	akpm@...ux-foundation.org,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	linux-kernel@...r.kernel.org, linux-arch@...r.kernel.org,
	David Miller <davem@...emloft.net>,
	Hugh Dickins <hugh.dickins@...cali.co.uk>,
	Mel Gorman <mel@....ul.ie>, Nick Piggin <npiggin@...e.de>
Subject: Re: [PATCH 07/13] powerpc: Preemptible mmu_gather

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 ;-)
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