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Message-ID: <1448312664.19320.9.camel@hpe.com>
Subject: Re: [PATCH] dax: Split pmd map when fallback on COW
From: Toshi Kani <toshi.kani@hpe.com>
To: Dan Williams <dan.j.williams@intel.com>
Cc: "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>,
        Matthew Wilcox <willy@linux.intel.com>,
        Ross Zwisler <ross.zwisler@linux.intel.com>,
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Date: Mon, 23 Nov 2015 14:04:24 -0700
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On Mon, 2015-11-23 at 12:56 -0800, Dan Williams wrote:
> On Mon, Nov 23, 2015 at 12:45 PM, Toshi Kani <toshi.kani@hpe.com> wrote:
> > On Mon, 2015-11-23 at 12:45 -0800, Dan Williams wrote:
> > > On Mon, Nov 23, 2015 at 12:05 PM, Toshi Kani <toshi.kani@hpe.com> wrote:
> [..]
> > > This is a nop if CONFIG_TRANSPARENT_HUGEPAGE=n, so I don't think it's
> > > a complete fix.
> > 
> > Well, __dax_pmd_fault() itself depends on CONFIG_TRANSPARENT_HUGEPAGE.
> > 
> 
> Indeed it is... I think that's wrong because transparent huge pages
> rely on struct page??

I do not think this issue is related with struct page.  wp_huge_pmd() calls
either do_huge_pmd_wp_page() or dax_pmd_fault().  do_huge_pmd_wp_page() splits a
pmd page when it returns with VM_FAULT_FALLBACK.  So, this change keeps them
consistent on VM_FAULT_FALLBACK.

Thanks,
-Toshi