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Re: [PATCH v5 2/5] allow mapping page-less memremaped areas into KVA

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On 08/13/2015 05:48 PM, Boaz Harrosh wrote:
<>
> There is already an object that holds a relationship of physical
> to Kernel-virtual. It is called a memory-section. Why not just
> widen its definition?
> 

BTW: Regarding the "widen its definition"

I was thinking of two possible new models here:
[1-A page-less memory section]
- Keep the 64bit phisical-to-kernel_virtual hard coded relationship
- Allocate a section-object, but this section object does not have any
  pages, its only the header. (You need it for the pmd/pmt thing)

  Lots of things just work now if you make sure you do not go through
  a page struct. This needs no extra work I have done this in the past
  all you need is to do your ioremap through the map_kernel_range_noflush(__va(), ....)

[2- Small pages-struct]

- Like above, but each entry in the new section object is small one-ulong size
  holding just flags.

 Then if !(p->flags & PAGE_SPECIAL) page = container_of(p, struct page, flags)

 This model is good because you actually have your pfn_to_page and page_to_pfn
 and need not touch sg-list or bio. But only 8 bytes per frame instead of 64 bytes


But I still think that the best long-term model is the variable size pages
where a page* can be 2M or 1G. Again an extra flag and a widen section definition.
Is about time we move to bigger pages, throughout but still keep the 4k
page-cache-dirty granularity.

Thanks
Boaz

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[PATCH v5 0/5] introduce __pfn_t for unmapped pfn I/O and DAX  lifetime Dan Williams <dan.j.williams@intel.com> - 2015-08-13 05:10 +0200
  [PATCH v5 1/5] mm: move __phys_to_pfn and __pfn_to_phys to  asm/generic/memory_model.h Dan Williams <dan.j.williams@intel.com> - 2015-08-13 05:10 +0200
  [PATCH v5 5/5] scatterlist: convert to __pfn_t Dan Williams <dan.j.williams@intel.com> - 2015-08-13 05:10 +0200
  [PATCH v5 3/5] dax: drop size parameter to ->direct_access() Dan Williams <dan.j.williams@intel.com> - 2015-08-13 05:10 +0200
  [PATCH v5 2/5] allow mapping page-less memremaped areas into KVA Dan Williams <dan.j.williams@intel.com> - 2015-08-13 05:10 +0200
    Re: [PATCH v5 2/5] allow mapping page-less memremaped areas into  KVA Boaz Harrosh <boaz@plexistor.com> - 2015-08-13 08:00 +0200
      Re: [PATCH v5 2/5] allow mapping page-less memremaped areas into KVA Dan Williams <dan.j.williams@intel.com> - 2015-08-13 15:00 +0200
        Re: [PATCH v5 2/5] allow mapping page-less memremaped areas into  KVA Boaz Harrosh <boaz@plexistor.com> - 2015-08-13 15:30 +0200
          Re: [PATCH v5 2/5] allow mapping page-less memremaped areas into  KVA Christoph Hellwig <hch@lst.de> - 2015-08-13 16:50 +0200
            Re: [PATCH v5 2/5] allow mapping page-less memremaped areas into  KVA Boaz Harrosh <boaz@plexistor.com> - 2015-08-13 17:10 +0200
      Re: [PATCH v5 2/5] allow mapping page-less memremaped areas into  KVA Christoph Hellwig <hch@lst.de> - 2015-08-13 16:40 +0200
        Re: [PATCH v5 2/5] allow mapping page-less memremaped areas into  KVA Boaz Harrosh <boaz@plexistor.com> - 2015-08-13 16:50 +0200
          Re: [PATCH v5 2/5] allow mapping page-less memremaped areas into  KVA Boaz Harrosh <boaz@plexistor.com> - 2015-08-13 17:30 +0200
          Re: [PATCH v5 2/5] allow mapping page-less memremaped areas into  KVA Dave Hansen <dave@sr71.net> - 2015-08-13 19:40 +0200
    Re: [PATCH v5 2/5] allow mapping page-less memremaped areas into KVA Matthew Wilcox <willy@linux.intel.com> - 2015-08-13 19:40 +0200
      Re: [PATCH v5 2/5] allow mapping page-less memremaped areas into KVA Dan Williams <dan.j.williams@intel.com> - 2015-08-13 20:20 +0200
  [PATCH v5 4/5] dax: fix mapping lifetime handling,  convert to __pfn_t + kmap_atomic_pfn_t() Dan Williams <dan.j.williams@intel.com> - 2015-08-13 05:10 +0200
    Re: [PATCH v5 4/5] dax: fix mapping lifetime handling, convert to  __pfn_t + kmap_atomic_pfn_t() Boaz Harrosh <boaz@plexistor.com> - 2015-08-13 08:30 +0200
      Re: [PATCH v5 4/5] dax: fix mapping lifetime handling, convert to  __pfn_t + kmap_atomic_pfn_t() Dan Williams <dan.j.williams@intel.com> - 2015-08-13 17:30 +0200
        Re: [PATCH v5 4/5] dax: fix mapping lifetime handling, convert to  __pfn_t + kmap_atomic_pfn_t() Boaz Harrosh <boaz@plexistor.com> - 2015-08-13 18:40 +0200
          Re: [PATCH v5 4/5] dax: fix mapping lifetime handling, convert to  __pfn_t + kmap_atomic_pfn_t() Dan Williams <dan.j.williams@intel.com> - 2015-08-13 21:00 +0200

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