Dan Williams <dan.j.williams(a)intel.com> writes:
On Mon, May 7, 2018 at 12:08 PM, Jeff Moyer <jmoyer(a)redhat.com>
> Dan Williams <dan.j.williams(a)intel.com> writes:
>> On Mon, May 7, 2018 at 11:46 AM, Matthew Wilcox <willy(a)infradead.org>
>>> On Mon, May 07, 2018 at 10:50:21PM +0800, Huaisheng Ye wrote:
>>>> Traditionally, NVDIMMs are treated by mm(memory management) subsystem as
>>>> DEVICE zone, which is a virtual zone and both its start and end of pfn
>>>> are equal to 0, mm wouldn’t manage NVDIMM directly as DRAM, kernel uses
>>>> corresponding drivers, which locate at \drivers\nvdimm\ and
>>>> \drivers\acpi\nfit and fs, to realize NVDIMM memory alloc and free with
>>>> memory hot plug implementation.
>>> You probably want to let linux-nvdimm know about this patch set.
>>> Adding to the cc.
>> Yes, thanks for that!
>>> Also, I only received patch 0 and 4. What happened
>>> to 1-3,5 and 6?
>>>> With current kernel, many mm’s classical features like the buddy
>>>> system, swap mechanism and page cache couldn’t be supported to NVDIMM.
>>>> What we are doing is to expand kernel mm’s capacity to make it to handle
>>>> NVDIMM like DRAM. Furthermore we make mm could treat DRAM and NVDIMM
>>>> separately, that means mm can only put the critical pages to NVDIMM
> Please define "critical pages."
>>>> zone, here we created a new zone type as NVM zone. That is to say for
>>>> traditional(or normal) pages which would be stored at DRAM scope like
>>>> Normal, DMA32 and DMA zones. But for the critical pages, which we hope
>>>> them could be recovered from power fail or system crash, we make them
>>>> to be persistent by storing them to NVM zone.
>> I think adding yet one more mm-zone is the wrong direction. Instead,
>> what we have been considering is a mechanism to allow a device-dax
>> instance to be given back to the kernel as a distinct numa node
>> managed by the VM. It seems it times to dust off those patches.
> What's the use case?
Use NVDIMMs as System-RAM given their potentially higher capacity than
DDR. The expectation in that case is that data is forfeit (not
persisted) after a crash. Any persistent use case would need to go
through the pmem driver, filesystem-dax or device-dax.
OK, but that sounds different from what was being proposed, here. I'll
quote from above:
>>>> But for the critical pages, which we hope them could
>>>> from power fail or system crash, we make them to be
>>>> storing them to NVM zone.
Hence my confusion.