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From:   Jeff Moyer <jmoyer@redhat.com>
To:     "Li\, Zhijian" <lizhijian@cn.fujitsu.com>
Cc:     Jason Gunthorpe <jgg@ziepe.ca>, <linux-rdma@vger.kernel.org>,
        <zyjzyj2000@gmail.com>, <aharonl@nvidia.com>, <leon@kernel.org>,
        <linux-kernel@vger.kernel.org>, <mbloch@nvidia.com>,
        <liangwenpeng@huawei.com>, <yangx.jy@cn.fujitsu.com>,
        <rpearsonhpe@gmail.com>, <y-goto@fujitsu.com>,
        <dan.j.williams@intel.com>,
        "nvdimm\@lists.linux.dev" <nvdimm@lists.linux.dev>
Subject: Re: [RFC PATCH rdma-next 01/10] RDMA: mr: Introduce is_pmem
References: <20211228080717.10666-1-lizhijian@cn.fujitsu.com>
        <20211228080717.10666-2-lizhijian@cn.fujitsu.com>
        <20220106002130.GP6467@ziepe.ca>
        <bf038e6c-66db-50ca-0126-3ad4ac1371e7@fujitsu.com>
        <4e679df5-633d-cd0c-9de3-16348b2cef35@cn.fujitsu.com>
Date:   Thu, 27 Jan 2022 17:30:08 -0500
In-Reply-To: <4e679df5-633d-cd0c-9de3-16348b2cef35@cn.fujitsu.com> (Zhijian
        Li's message of "Fri, 14 Jan 2022 16:10:33 +0800")
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"Li, Zhijian" <lizhijian@cn.fujitsu.com> writes:

> Copied to nvdimm list
>
> Thanks
>
> Zhijian
>
>
> on 2022/1/6 14:12, Li Zhijian wrote:
>>
>> Add Dan to the party :)
>>
>> May i know whether there is any existing APIs to check whether
>> a va/page backs to a nvdimm/pmem ?

I don't know of one.  You could try walk_system_ram_range looking for
IORES_DESC_PERSISTENT_MEMORY, but that's not very efficient.

>>> You need to get Dan to check this out, but I'm pretty sure this should
>>> be more like this:
>>>
>>> if (is_zone_device_page(page) && page->pgmap->type ==
>>> MEMORY_DEVICE_FS_DAX)

You forgot MEMORY_DEVICE_GENERIC.  However, this doesn't guarantee the
memory belongs to persistent memory, only that it is direct access
capable.

Dan, any ideas?

-Jeff