Date: Fri, 8 May 2015 15:21:49 -0700
From: Andrew Morton <akpm@linux-foundation.org>
To: "Aneesh Kumar K.V" <aneesh.kumar@linux.vnet.ibm.com>
Cc: mpe@ellerman.id.au, paulus@samba.org, benh@kernel.crashing.org,
        kirill.shutemov@linux.intel.com, aarcange@redhat.com,
        linux-mm@kvack.org, linux-kernel@vger.kernel.org,
        linuxppc-dev@lists.ozlabs.org
Subject: Re: [PATCH V2 2/2] powerpc/thp: Serialize pmd clear against a linux
 page table walk.
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	<1430983408-24924-2-git-send-email-aneesh.kumar@linux.vnet.ibm.com>
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On Thu,  7 May 2015 12:53:28 +0530 "Aneesh Kumar K.V" <aneesh.kumar@linux.vnet.ibm.com> wrote:

> Serialize against find_linux_pte_or_hugepte which does lock-less
> lookup in page tables with local interrupts disabled. For huge pages
> it casts pmd_t to pte_t. Since format of pte_t is different from
> pmd_t we want to prevent transit from pmd pointing to page table
> to pmd pointing to huge page (and back) while interrupts are disabled.
> We clear pmd to possibly replace it with page table pointer in
> different code paths. So make sure we wait for the parallel
> find_linux_pte_or_hugepage to finish.

I'm not seeing here any description of the problem which is being
fixed.  Does the patch make the machine faster?  Does the machine
crash?
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