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Subject: Re: [PATCH v2 11/11] powerpc/mm/book3s64/pgtable: Uses counting
 method to skip serializing
To:     Leonardo Bras <leonardo@linux.ibm.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>,
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        Keith Busch <keith.busch@intel.com>,
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        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>
References: <20190920195047.7703-1-leonardo@linux.ibm.com>
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 <1b39eaa7-751d-40bc-d3d7-41aaa15be42a@nvidia.com>
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From:   John Hubbard <jhubbard@nvidia.com>
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On 9/23/19 1:23 PM, Leonardo Bras wrote:
> On Mon, 2019-09-23 at 12:58 -0700, John Hubbard wrote:
>>
>> CPU 0                            CPU 1
>> ------                         --------------
>>                                READ(pte) (re-ordered at run time)
>>                                atomic_inc(val) (no run-time memory barrier!)
>>                            
>> pmd_clear(pte)
>> if (val)
>>     run_on_all_cpus(): IPI
>>                                local_irq_disable() (also not a mem barrier)
>>
>>                                if(pte)
>>                                   walk page tables
> 
> Let me see if I can understand,
> On most patches, it would be:
> 
> CPU 0                            CPU 1
> ------				--------------
> 				ptep = __find_linux_pte  
> 				(re-ordered at run time)
> 				atomic_inc(val) 
> pmd_clear(pte)
> smp_mb()
> if (val)
>     run_on_all_cpus(): IPI
>                                local_irq_disable() 
> 
>                                if(ptep)
>                                   pte = *ptep;
> 
> Is that what you meant?
> 
> 

Yes.

thanks,
-- 
John Hubbard
NVIDIA

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Subject: Re: [PATCH v2 11/11] powerpc/mm/book3s64/pgtable: Uses counting
 method to skip serializing
To: Leonardo Bras <leonardo@linux.ibm.com>, <linuxppc-dev@lists.ozlabs.org>,
 <linux-kernel@vger.kernel.org>, Linux-MM <linux-mm@kvack.org>
References: <20190920195047.7703-1-leonardo@linux.ibm.com>
 <20190920195047.7703-12-leonardo@linux.ibm.com>
 <1b39eaa7-751d-40bc-d3d7-41aaa15be42a@nvidia.com>
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From: John Hubbard <jhubbard@nvidia.com>
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Date: Mon, 23 Sep 2019 13:26:48 -0700
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On 9/23/19 1:23 PM, Leonardo Bras wrote:
> On Mon, 2019-09-23 at 12:58 -0700, John Hubbard wrote:
>>
>> CPU 0                            CPU 1
>> ------                         --------------
>>                                READ(pte) (re-ordered at run time)
>>                                atomic_inc(val) (no run-time memory barrier!)
>>                            
>> pmd_clear(pte)
>> if (val)
>>     run_on_all_cpus(): IPI
>>                                local_irq_disable() (also not a mem barrier)
>>
>>                                if(pte)
>>                                   walk page tables
> 
> Let me see if I can understand,
> On most patches, it would be:
> 
> CPU 0                            CPU 1
> ------				--------------
> 				ptep = __find_linux_pte  
> 				(re-ordered at run time)
> 				atomic_inc(val) 
> pmd_clear(pte)
> smp_mb()
> if (val)
>     run_on_all_cpus(): IPI
>                                local_irq_disable() 
> 
>                                if(ptep)
>                                   pte = *ptep;
> 
> Is that what you meant?
> 
> 

Yes.

thanks,
-- 
John Hubbard
NVIDIA