linux-kernel - Re: [PATCH -v2 1/4] mm: Rework {set,clear,mm}_tlb_flush

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Date:   Thu, 3 Aug 2017 16:27:36 +0100
From:   Will Deacon <will.deacon@....com>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     torvalds@...ux-foundation.org, oleg@...hat.com,
        paulmck@...ux.vnet.ibm.com, benh@...nel.crashing.org,
        mpe@...erman.id.au, npiggin@...il.com,
        linux-kernel@...r.kernel.org, mingo@...nel.org,
        stern@...land.harvard.edu, Russell King <linux@...linux.org.uk>,
        Heiko Carstens <heiko.carstens@...ibm.com>,
        Ralf Baechle <ralf@...ux-mips.org>,
        Vineet Gupta <vgupta@...opsys.com>,
        "David S. Miller" <davem@...emloft.net>,
        Mel Gorman <mgorman@...e.de>, Rik van Riel <riel@...hat.com>
Subject: Re: [PATCH -v2 1/4] mm: Rework {set,clear,mm}_tlb_flush_pending()

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@....com>

Will