Re: [PATCH v9 10/10] drivers/block/pmem: Map NVDIMM with ioremap_wt()

[Dan Williams]

On Wed, May 13, 2015 at 2:05 PM, Toshi Kani <toshi.kani@xxxxxx> wrote:
> The pmem driver maps NVDIMM with ioremap_nocache() as we cannot
> write back the contents of the CPU caches in case of a crash.
>
> This patch changes to use ioremap_wt(), which provides uncached
> writes but cached reads, for improving read performance.

I'm thinking that for the libnd integration we don't want the pmem
driver hard coding the cache-policy decision.  This is something that
should be specified to nd_pmem_region_create().  Especially
considering that platform firmware tables (NFIT) may specify the cache
policy for the range.  As Matthew Wilcox mentioned offline we also
must match the DAX-to-mmap cache policy with the policy for the driver
mapping  for architectures that are not capable of multiple mappings
of the same physical address with different policies.
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