Re: [PATCH 0/9] Allow persistent memory to be used like normal RAM

[Yang Shi]

On Mon, Oct 22, 2018 at 1:18 PM Dave Hansen <dave.hansen@xxxxxxxxxxxxxxx> wrote:
>
> Persistent memory is cool.  But, currently, you have to rewrite
> your applications to use it.  Wouldn't it be cool if you could
> just have it show up in your system like normal RAM and get to
> it like a slow blob of memory?  Well... have I got the patch
> series for you!
>
> This series adds a new "driver" to which pmem devices can be
> attached.  Once attached, the memory "owned" by the device is
> hot-added to the kernel and managed like any other memory.  On
> systems with an HMAT (a new ACPI table), each socket (roughly)
> will have a separate NUMA node for its persistent memory so
> this newly-added memory can be selected by its unique NUMA
> node.

Could you please elaborate this? I'm supposed you mean the pmem will
be a separate NUMA node, right?

I would like to try the patches on real hardware, any prerequisite is needed?

Thanks,
Yang

>
> This is highly RFC, and I really want the feedback from the
> nvdimm/pmem folks about whether this is a viable long-term
> perversion of their code and device mode.  It's insufficiently
> documented and probably not bisectable either.
>
> Todo:
> 1. The device re-binding hacks are ham-fisted at best.  We
>    need a better way of doing this, especially so the kmem
>    driver does not get in the way of normal pmem devices.
> 2. When the device has no proper node, we default it to
>    NUMA node 0.  Is that OK?
> 3. We muck with the 'struct resource' code quite a bit. It
>    definitely needs a once-over from folks more familiar
>    with it than I.
> 4. Is there a better way to do this than starting with a
>    copy of pmem.c?
>
> Here's how I set up a system to test this thing:
>
> 1. Boot qemu with lots of memory: "-m 4096", for instance
> 2. Reserve 512MB of physical memory.  Reserving a spot a 2GB
>    physical seems to work: memmap=512M!0x0000000080000000
>    This will end up looking like a pmem device at boot.
> 3. When booted, convert fsdax device to "device dax":
>         ndctl create-namespace -fe namespace0.0 -m dax
> 4. In the background, the kmem driver will probably bind to the
>    new device.
> 5. Now, online the new memory sections.  Perhaps:
>
> grep ^MemTotal /proc/meminfo
> for f in `grep -vl online /sys/devices/system/memory/*/state`; do
>         echo $f: `cat $f`
>         echo online > $f
>         grep ^MemTotal /proc/meminfo
> done
>
> Cc: Dan Williams <dan.j.williams@xxxxxxxxx>
> Cc: Dave Jiang <dave.jiang@xxxxxxxxx>
> Cc: Ross Zwisler <zwisler@xxxxxxxxxx>
> Cc: Vishal Verma <vishal.l.verma@xxxxxxxxx>
> Cc: Tom Lendacky <thomas.lendacky@xxxxxxx>
> Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
> Cc: Michal Hocko <mhocko@xxxxxxxx>
> Cc: linux-nvdimm@xxxxxxxxxxxx
> Cc: linux-kernel@xxxxxxxxxxxxxxx
> Cc: linux-mm@xxxxxxxxx
> Cc: Huang Ying <ying.huang@xxxxxxxxx>
> Cc: Fengguang Wu <fengguang.wu@xxxxxxxxx>
>