Re: [-mm PATCH v4 15/18] mm, dax: dax-pmd vs thp-pmd vs hugetlbfs-pmd

["Williams, Dan J" <dan.j.williams@intel.com>]

On Sun, 2015-12-20 at 21:45 -0800, Dan Williams wrote:
> A dax-huge-page mapping while it uses some thp helpers is ultimately not a
> transparent huge page.  The distinction is especially important in the
> get_user_pages() path.  pmd_devmap() is used to distinguish dax-pmds from
> pmd_huge() and pmd_trans_huge() which have slightly different semantics.
> 
> Explicitly mark the pmd_trans_huge() helpers that dax needs by adding
> pmd_devmap() checks.
> 
> Cc: Dave Hansen <dave@sr71.net>
> Cc: Mel Gorman <mgorman@suse.de>
> Cc: Peter Zijlstra <peterz@infradead.org>
> Cc: Andrea Arcangeli <aarcange@redhat.com>
> Cc: Matthew Wilcox <willy@linux.intel.com>
> Cc: Andrew Morton <akpm@linux-foundation.org>
> Cc: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
> Signed-off-by: Dan Williams <dan.j.williams@intel.com>
> 
[..]
> diff --git a/include/linux/mm.h b/include/linux/mm.h
> index 957afd1b10a5..96f396bbcc9f 100644
> --- a/include/linux/mm.h
> +++ b/include/linux/mm.h
> @@ -1471,6 +1471,13 @@ static inline int __pud_alloc(struct mm_struct *mm, pgd_t *pgd,
>  int __pud_alloc(struct mm_struct *mm, pgd_t *pgd, unsigned long address);
>  #endif
>  
> +#if !defined(__HAVE_ARCH_PTE_DEVMAP) || !defined(CONFIG_TRANSPARENT_HUGEPAGE)
> +static inline int pmd_devmap(pmd_t pmd)
> +{
> +	return 0;
> +}
> +#endif
> +

Andrew, here's an incremental fix to fold into this patch.

8<---
Subject: mm: fix pmd_devmap compile error

From: Dan Williams <dan.j.williams@intel.com>

The kbuild robot reports the following with an i386 randconfig:

   In file included from arch/x86/include/asm/atomic.h:4:0,
                    from include/linux/atomic.h:4,
                    from include/linux/crypto.h:20,
                    from arch/x86/kernel/asm-offsets.c:8:
   include/linux/huge_mm.h: In function 'pmd_trans_huge_lock':
>> include/linux/huge_mm.h:128:30: error: implicit declaration of function 'pmd_devmap' [-Werror=implicit-function-declaration]
     if (pmd_trans_huge(*pmd) || pmd_devmap(*pmd))
                                 ^
Fix by moving the fallback definition of pmd_devmap() earlier in mm.h,
before it include huge_mm.h.

Reported-by: kbuild test robot <lkp@intel.com>
Signed-off-by: Dan Williams <dan.j.williams@intel.com>
---
 include/linux/mm.h |   14 +++++++-------
 1 file changed, 7 insertions(+), 7 deletions(-)

diff --git a/include/linux/mm.h b/include/linux/mm.h
index d802df18f08a..9f934b4235ca 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -342,6 +342,13 @@ struct inode;
 #define page_private(page)		((page)->private)
 #define set_page_private(page, v)	((page)->private = (v))
 
+#if !defined(__HAVE_ARCH_PTE_DEVMAP) || !defined(CONFIG_TRANSPARENT_HUGEPAGE)
+static inline int pmd_devmap(pmd_t pmd)
+{
+	return 0;
+}
+#endif
+
 /*
  * FIXME: take this include out, include page-flags.h in
  * files which need it (119 of them)
@@ -1487,13 +1494,6 @@ static inline int __pud_alloc(struct mm_struct *mm, pgd_t *pgd,
 int __pud_alloc(struct mm_struct *mm, pgd_t *pgd, unsigned long address);
 #endif
 
-#if !defined(__HAVE_ARCH_PTE_DEVMAP) || !defined(CONFIG_TRANSPARENT_HUGEPAGE)
-static inline int pmd_devmap(pmd_t pmd)
-{
-	return 0;
-}
-#endif
-
 #ifndef __HAVE_ARCH_PTE_DEVMAP
 static inline int pte_devmap(pte_t pte)
 {
--
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