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Date: Thu, 3 Aug 2017 16:27:36 +0100
From: Will Deacon <will.deacon@arm.com>
To: Peter Zijlstra <peterz@infradead.org>
Cc: torvalds@linux-foundation.org, oleg@redhat.com,
        paulmck@linux.vnet.ibm.com, benh@kernel.crashing.org,
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        "David S. Miller" <davem@davemloft.net>, Mel Gorman <mgorman@suse.de>,
        Rik van Riel <riel@redhat.com>
Subject: Re: [PATCH -v2 1/4] mm: Rework {set,clear,mm}_tlb_flush_pending()
Message-ID: <20170803152735.GC20783@arm.com>
References: <20170802113837.280183420@infradead.org>
 <20170802114030.020058451@infradead.org>
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On Wed, Aug 02, 2017 at 01:38:38PM +0200, Peter Zijlstra wrote:
> Commit:
> 
>   af2c1401e6f9 ("mm: numa: guarantee that tlb_flush_pending updates are visible before page table updates")
> 
> added smp_mb__before_spinlock() to set_tlb_flush_pending(). I think we
> can solve the same problem without this barrier.
> 
> If instead we mandate that mm_tlb_flush_pending() is used while
> holding the PTL we're guaranteed to observe prior
> set_tlb_flush_pending() instances.
> 
> For this to work we need to rework migrate_misplaced_transhuge_page()
> a little and move the test up into do_huge_pmd_numa_page().
> 
> NOTE: this relies on flush_tlb_range() to guarantee:
> 
>    (1) it ensures that prior page table updates are visible to the
>        page table walker and
>    (2) it ensures that subsequent memory accesses are only made
>        visible after the invalidation has completed

Works for me:

Acked-by: Will Deacon <will.deacon@arm.com>

Will