Re: [PATCH v4 1/6] libnvdimm/namespace: Make namespace size validation arch dependent

On 1/24/20 10:15 PM, Dan Williams wrote:

On Thu, Jan 23, 2020 at 11:34 PM Aneesh Kumar K.V
[off-list ref] wrote:

quoted

On 1/24/20 11:27 AM, Dan Williams wrote:

quoted

On Mon, Jan 20, 2020 at 6:08 AM Aneesh Kumar K.V

....

quoted

quoted

+unsigned long arch_namespace_map_size(void)
+{
+       return PAGE_SIZE;
+}
+EXPORT_SYMBOL_GPL(arch_namespace_map_size);
+
+
   static void __cpa_flush_all(void *arg)
   {
          unsigned long cache = (unsigned long)arg;

diff --git a/include/linux/libnvdimm.h b/include/linux/libnvdimm.h
index 9df091bd30ba..a3476dbd2656 100644
--- a/include/linux/libnvdimm.h
+++ b/include/linux/libnvdimm.h

@@ -284,4 +284,5 @@ static inline void arch_invalidate_pmem(void *addr, size_t size)
   }
   #endif

+unsigned long arch_namespace_map_size(void);

This property is more generic than the nvdimm namespace mapping size,
it's more the fundamental remap granularity that the architecture
supports. So I would expect this to be defined in core header files.
Something like:

diff --git a/include/linux/io.h b/include/linux/io.h
index a59834bc0a11..58b3b2091dbb 100644
--- a/include/linux/io.h
+++ b/include/linux/io.h

@@ -155,6 +155,13 @@ enum {
   void *memremap(resource_size_t offset, size_t size, unsigned long flags);
   void memunmap(void *addr);

+#ifndef memremap_min_align
+static inline unsigned int memremap_min_align(void)
+{
+       return PAGE_SIZE;
+}
+#endif
+

Should that be memremap_pages_min_align()?

No, and on second look it needs to be a common value that results in
properly aligned / sized namespaces across architectures.

What would it take for Power to make it's minimum mapping granularity
SUBSECTION_SIZE? The minute that the minimum alignment changes across
architectures we lose compatibility.

The namespaces need to be sized such that the mode can be changed freely.

Linux on ppc64 with hash translation use just one page size for direct mapping and that is 16MB.

-aneesh