Groups > linux.kernel > #1207316

Re: [PATCH 29/31] parisc: handle page-less SG entries

From	Dan Williams <dan.j.williams@intel.com>
Newsgroups	linux.kernel
Subject	Re: [PATCH 29/31] parisc: handle page-less SG entries
Date	2015-08-14 05:40 +0200
Message-ID	<pXe0x-6PB-1@gated-at.bofh.it> (permalink)
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On Thu, Aug 13, 2015 at 7:31 AM, Christoph Hellwig <hch@lst.de> wrote:
> On Wed, Aug 12, 2015 at 09:01:02AM -0700, Linus Torvalds wrote:
>> I'm assuming that anybody who wants to use the page-less
>> scatter-gather lists always does so on memory that isn't actually
>> virtually mapped at all, or only does so on sane architectures that
>> are cache coherent at a physical level, but I'd like that assumption
>> *documented* somewhere.
>
> It's temporarily mapped by kmap-like helpers.  That code isn't in
> this series. The most recent version of it is here:
>
> https://git.kernel.org/cgit/linux/kernel/git/djbw/nvdimm.git/commit/?h=pfn&id=de8237c99fdb4352be2193f3a7610e902b9bb2f0
>
> note that it's not doing the cache flushing it would have to do yet, but
> it's also only enabled for x86 at the moment.

For virtually tagged caches I assume we would temporarily map with
kmap_atomic_pfn_t(), similar to how drm_clflush_pages() implements
powerpc support.  However with DAX we could end up with multiple
virtual aliases for a page-less pfn.
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Thread

[PATCH 29/31] parisc: handle page-less SG entries Christoph Hellwig <hch@lst.de> - 2015-08-12 09:20 +0200
  Re: [PATCH 29/31] parisc: handle page-less SG entries Linus Torvalds <torvalds@linux-foundation.org> - 2015-08-12 18:10 +0200
    Re: [PATCH 29/31] parisc: handle page-less SG entries Christoph Hellwig <hch@lst.de> - 2015-08-13 16:40 +0200
      Re: [PATCH 29/31] parisc: handle page-less SG entries Dan Williams <dan.j.williams@intel.com> - 2015-08-14 05:40 +0200
        Re: [PATCH 29/31] parisc: handle page-less SG entries James Bottomley <James.Bottomley@HansenPartnership.com> - 2015-08-14 06:00 +0200
          Re: [PATCH 29/31] parisc: handle page-less SG entries David Miller <davem@davemloft.net> - 2015-08-14 06:20 +0200
            Re: [PATCH 29/31] parisc: handle page-less SG entries Dan Williams <dan.j.williams@intel.com> - 2015-08-14 18:20 +0200

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