linux-kernel - Re: [RFC PATCH rdma-next 01/10] RDMA: mr: Introduce is

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Date:   Thu, 27 Jan 2022 17:30:08 -0500
From:   Jeff Moyer <jmoyer@...hat.com>
To:     "Li\, Zhijian" <lizhijian@...fujitsu.com>
Cc:     Jason Gunthorpe <jgg@...pe.ca>, <linux-rdma@...r.kernel.org>,
        <zyjzyj2000@...il.com>, <aharonl@...dia.com>, <leon@...nel.org>,
        <linux-kernel@...r.kernel.org>, <mbloch@...dia.com>,
        <liangwenpeng@...wei.com>, <yangx.jy@...fujitsu.com>,
        <rpearsonhpe@...il.com>, <y-goto@...itsu.com>,
        <dan.j.williams@...el.com>,
        "nvdimm\@lists.linux.dev" <nvdimm@...ts.linux.dev>
Subject: Re: [RFC PATCH rdma-next 01/10] RDMA: mr: Introduce is_pmem

"Li, Zhijian" <lizhijian@...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