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Subject: Re: [PATCH] pramdisk: new block disk driver to perform persistent
 storage
To: Dan Williams <dan.j.williams@intel.com>,
        Ross Zwisler <ross.zwisler@linux.intel.com>
References: <1442562390-91051-1-git-send-email-linyongting@huawei.com>
 <20150918161813.GA4274@linux.intel.com>
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CC: Jens Axboe <axboe@fb.com>, Andrew Morton <akpm@linux-foundation.org>,
        Richard Weinberger <richard@nod.at>,
        Matthew Wilcox <willy@linux.intel.com>, <wangxiaozhe@huawei.com>,
        Ingo Molnar <mingo@kernel.org>, Greg KH <gregkh@linuxfoundation.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>
From: Lin Yongting <linyongting@huawei.com>
Message-ID: <55FFCF75.70005@huawei.com>
Date: Mon, 21 Sep 2015 17:35:49 +0800
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On 2015/9/19 0:41, Dan Williams wrote:
> On Fri, Sep 18, 2015 at 9:18 AM, Ross Zwisler
> <ross.zwisler@linux.intel.com> wrote:
>> On Fri, Sep 18, 2015 at 03:46:30PM +0800, Lin Yongting wrote:
>>> In embed devices, user space applications will use reserved memory
>>> (i.e. persistent memory) to store business data, the data is kept
>>> in this memory region after system rebooting or panic.
>>>
>>> pramdisk is a block disk driver based on Persistent memory, it provide
>>> file system interface for application to read/write data in persistent
>>> memory. Application can use pramdisk to store log file or business data
>>> in persistent memory in the way of file system operation, avoid operating
>>> or managing memory directly.
>>>
>>> pramdisk support multiple Persistent menory regions and each one is a
>>> block device named as /dev/pram<N>.
>>>
>>> Usage:
>>> modprobe pramdisk.ko pmem=<size1>@<addr2> [ pmem=<size2>@<addr2> ... ]
>>>
>>> For example:
>>>    modprobe pramdisk.ko pmem=20M@2050M pmem=20M@2150M
>>>    mkfs.ext3 /dev/pram1
>>>    mkdir /tmp/test1
>>>    mount -t ext3 /dev/pram1 /tmp/test1
>>>
>>> Signed-off-by: Lin Yongting <linyongting@huawei.com>
>>> Signed-off-by: Wang xiaozhe <wangxiaozhe@huawei.com>
>>
>> I think you already have this functionality with the PMEM driver and the
>> memmap=nn[KMG]!ss[KMG] command line parameter?  What are you trying to
>> accomplish with this driver that you can't do with PMEM?
>
> Moreover, if your embedded firmware publishes persistent memory ranges
> you can reuse the drivers/nvdimm/e820.c driver.  As long as your
> platform code in the kernel names those iomem_resource(s) as
> ""Persistent Memory (legacy)" they will be auto discovered and
> surfaced by the libnvidmm sub-system.
>

Thanks Dan!

Seems nvdimm sub-system can figure out my requirement.

Actually, my system is ARM arch, there is no any firmware but just a DDR memory. We reserved a memory region
which is out of OS-memory to store data Persistently, this memory region will not clear in rebooting or panic
as long as the power is not cut off.