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Message-ID: <c64d34118542d5c2d31b8f6b7802d2a29dac71ef.camel@linux.ibm.com>
Subject: Re: [PATCH v2 11/11] powerpc/mm/book3s64/pgtable: Uses counting
 method to skip serializing
From:   Leonardo Bras <leonardo@linux.ibm.com>
To:     John Hubbard <jhubbard@nvidia.com>, linuxppc-dev@lists.ozlabs.org,
        linux-kernel@vger.kernel.org, Linux-MM <linux-mm@kvack.org>
Cc:     Dan Williams <dan.j.williams@intel.com>,
        Arnd Bergmann <arnd@arndb.de>, Jason Gunthorpe <jgg@ziepe.ca>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        Mahesh Salgaonkar <mahesh@linux.vnet.ibm.com>,
        YueHaibing <yuehaibing@huawei.com>,
        Nicholas Piggin <npiggin@gmail.com>,
        Mike Rapoport <rppt@linux.ibm.com>,
        Keith Busch <keith.busch@intel.com>,
        Richard Fontana <rfontana@redhat.com>,
        Paul Mackerras <paulus@samba.org>,
        "Aneesh Kumar K.V" <aneesh.kumar@linux.ibm.com>,
        Ganesh Goudar <ganeshgr@linux.ibm.com>,
        Thomas Gleixner <tglx@linutronix.de>,
        Ira Weiny <ira.weiny@intel.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        Allison Randal <allison@lohutok.net>
Date:   Mon, 23 Sep 2019 17:23:03 -0300
In-Reply-To: <1568b3ef-cec9-bf47-edaa-c775c2f544fb@nvidia.com>
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On Mon, 2019-09-23 at 12:58 -0700, John Hubbard wrote:
>=20
> CPU 0                            CPU 1
> ------                         --------------
>                                READ(pte) (re-ordered at run time)
>                                atomic_inc(val) (no run-time memory barrie=
r!)
>                           =20
> pmd_clear(pte)
> if (val)
>     run_on_all_cpus(): IPI
>                                local_irq_disable() (also not a mem barrie=
r)
>=20
>                                if(pte)
>                                   walk page tables

Let me see if I can understand,
On most patches, it would be:

CPU 0                            CPU 1
------				--------------
				ptep =3D __find_linux_pte =20
				(re-ordered at run time)
				atomic_inc(val)=20
pmd_clear(pte)
smp_mb()
if (val)
    run_on_all_cpus(): IPI
                               local_irq_disable()=20

                               if(ptep)
                                  pte =3D *ptep;

Is that what you meant?


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