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Date: Tue, 18 Jul 2017 10:53:42 +0200
From: Ingo Molnar <mingo@kernel.org>
Subject: Re: [PATCH v4 10/10] x86/mm: Try to preserve old TLB entries using
 PCID
Message-ID: <20170718085341.nlt35dph4oukb4tc@gmail.com>
References: <cover.1498751203.git.luto@kernel.org>
 <cf600d28712daa8e2222c08a10f6c914edab54f2.1498751203.git.luto@kernel.org>
 <20170705121807.GF4941@worktop>
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 <20170705170219.ogjnswef3ufgeklz@hirez.programming.kicks-ass.net>
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To: Peter Zijlstra <peterz@infradead.org>
Cc: Andy Lutomirski <luto@kernel.org>, X86 ML <x86@kernel.org>, "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>, Borislav Petkov <bp@alien8.de>, Linus Torvalds <torvalds@linux-foundation.org>, Andrew Morton <akpm@linux-foundation.org>, Mel Gorman <mgorman@suse.de>, "linux-mm@kvack.org" <linux-mm@kvack.org>, Nadav Amit <nadav.amit@gmail.com>, Rik van Riel <riel@redhat.com>, Dave Hansen <dave.hansen@intel.com>, Arjan van de Ven <arjan@linux.intel.com>


* Peter Zijlstra <peterz@infradead.org> wrote:

> On Wed, Jul 05, 2017 at 09:04:39AM -0700, Andy Lutomirski wrote:
> > On Wed, Jul 5, 2017 at 5:18 AM, Peter Zijlstra <peterz@infradead.org> wrote:
> > > On Thu, Jun 29, 2017 at 08:53:22AM -0700, Andy Lutomirski wrote:
> > >> @@ -104,18 +140,20 @@ void switch_mm_irqs_off(struct mm_struct *prev, struct mm_struct *next,
> > >>
> > >>               /* Resume remote flushes and then read tlb_gen. */
> > >>               cpumask_set_cpu(cpu, mm_cpumask(next));
> > >
> > > Barriers should have a comment... what is being ordered here against
> > > what?
> > 
> > How's this comment?
> > 
> >         /*
> >          * Resume remote flushes and then read tlb_gen.  We need to do
> >          * it in this order: any inc_mm_tlb_gen() caller that writes a
> >          * larger tlb_gen than we read here must see our cpu set in
> >          * mm_cpumask() so that it will know to flush us.  The barrier
> >          * here synchronizes with inc_mm_tlb_gen().
> >          */
> 
> Slightly confusing, you mean this, right?
> 
> 
> 	cpumask_set_cpu(cpu, mm_cpumask());			inc_mm_tlb_gen();
> 
> 	MB							MB
> 
> 	next_tlb_gen = atomic64_read(&next->context.tlb_gen);	flush_tlb_others(mm_cpumask());
> 
> 
> which seems to make sense.

Btw., I'll wait for a v5 iteration before applying this last patch to tip:x86/mm.

Thanks,

	Ingo

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