linux-kernel - Re: [PATCH for-next v5 0/7] On-Demand Paging on SoftRoCE

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Message-ID: <e13270a2-c149-6194-b283-06fc38efbd9b@linux.dev>
Date:   Fri, 19 May 2023 18:20:47 +0800
From:   Guoqing Jiang <guoqing.jiang@...ux.dev>
To:     "Daisuke Matsuda (Fujitsu)" <matsuda-daisuke@...itsu.com>,
        "linux-rdma@...r.kernel.org" <linux-rdma@...r.kernel.org>,
        "leonro@...dia.com" <leonro@...dia.com>,
        "jgg@...dia.com" <jgg@...dia.com>,
        "zyjzyj2000@...il.com" <zyjzyj2000@...il.com>
Cc:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "rpearsonhpe@...il.com" <rpearsonhpe@...il.com>,
        "Xiao Yang (Fujitsu)" <yangx.jy@...itsu.com>,
        "Zhijian Li (Fujitsu)" <lizhijian@...itsu.com>,
        "Yasunori Gotou (Fujitsu)" <y-goto@...itsu.com>
Subject: Re: [PATCH for-next v5 0/7] On-Demand Paging on SoftRoCE



On 5/19/23 17:57, Daisuke Matsuda (Fujitsu) wrote:
> On Fri, May 19, 2023 3:42 PM Guoqing Jiang wrote:
>> Hello,
>>
>> On 5/18/23 16:21, Daisuke Matsuda wrote:
>>> [2] [PATCH for-next v3 0/7] On-Demand Paging on SoftRoCE
>>> https://lore.kernel.org/lkml/cover.1671772917.git.matsuda-daisuke@fujitsu.com/
>> Quote from above link
>>
>> "There is a problem that data on DAX-enabled filesystem cannot be
>> duplicated with
>> software RAID or other hardware methods."
>>
>> Could you elaborate a bit more about the problem or any links about it?
>> Thank you.
> I am not an expert of Pmems, but my understanding is as follows:
>
> Pmem (Persistent memory) is detected as memory device during boot process.
> Physical addresses are allocated to them just like other memory in DIMM slots,
> so system have to treat them differently from traditional storage devices like HDD/SSD.
>
> It may be technically possible to duplicate data using multiple Pmems, but the duplication
> is practically not useful. For traditional storage devices, you can hot-remove and hot-add
> them easily on failure. However, Pmems are not attached to hot-pluggable slots. You have
> to halt the system and open the cabinet to change out the Pmem. This means availability
> of the system is not improved with data duplication on the same host.

I guess pmem with block translation table type would be fine since it 
can be used
like normal storage device, but I am not pmem expert as well 😁.

Thanks,
Guoqing