linux-kernel - Re: [PATCH v2] mm: huge_memory: Change return type to vm_fault

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Date:   Wed, 25 Apr 2018 00:09:12 -0700 (PDT)
From:   David Rientjes <rientjes@...gle.com>
To:     Souptick Joarder <jrdr.linux@...il.com>
cc:     akpm@...ux-foundation.org, zi.yan@...rutgers.edu,
        dan.j.williams@...el.com, kirill.shutemov@...ux.intel.com,
        ross.zwisler@...ux.intel.com, n-horiguchi@...jp.nec.com,
        mhocko@...e.com, shli@...com, linux-kernel@...r.kernel.org,
        linux-mm@...ck.org
Subject: Re: [PATCH v2] mm: huge_memory: Change return type to vm_fault_t

On Wed, 25 Apr 2018, Souptick Joarder wrote:

> Use new return type vm_fault_t for fault handler. For
> now, this is just documenting that the function returns
> a VM_FAULT value rather than an errno. Once all instances
> are converted, vm_fault_t will become a distinct type.
> 
> Commit 1c8f422059ae ("mm: change return type to vm_fault_t")
> 
> Signed-off-by: Souptick Joarder <jrdr.linux@...il.com>
> Reviewed-by: Matthew Wilcox <mawilcox@...rosoft.com>
> ---
> v2: Updated the change log
> 
>  include/linux/huge_mm.h | 5 +++--
>  mm/huge_memory.c        | 4 ++--
>  2 files changed, 5 insertions(+), 4 deletions(-)
> 
> diff --git a/include/linux/huge_mm.h b/include/linux/huge_mm.h
> index a8a1262..d3bbf6b 100644
> --- a/include/linux/huge_mm.h
> +++ b/include/linux/huge_mm.h
> @@ -3,6 +3,7 @@
>  #define _LINUX_HUGE_MM_H
>  
>  #include <linux/sched/coredump.h>
> +#include <linux/mm_types.h>
>  
>  #include <linux/fs.h> /* only for vma_is_dax() */
>  
> @@ -46,9 +47,9 @@ extern bool move_huge_pmd(struct vm_area_struct *vma, unsigned long old_addr,
>  extern int change_huge_pmd(struct vm_area_struct *vma, pmd_t *pmd,
>  			unsigned long addr, pgprot_t newprot,
>  			int prot_numa);
> -int vmf_insert_pfn_pmd(struct vm_area_struct *vma, unsigned long addr,
> +vm_fault_t vmf_insert_pfn_pmd(struct vm_area_struct *vma, unsigned long addr,
>  			pmd_t *pmd, pfn_t pfn, bool write);
> -int vmf_insert_pfn_pud(struct vm_area_struct *vma, unsigned long addr,
> +vm_fault_t vmf_insert_pfn_pud(struct vm_area_struct *vma, unsigned long addr,
>  			pud_t *pud, pfn_t pfn, bool write);
>  enum transparent_hugepage_flag {
>  	TRANSPARENT_HUGEPAGE_FLAG,
> diff --git a/mm/huge_memory.c b/mm/huge_memory.c
> index 87ab9b8..1fe4705 100644
> --- a/mm/huge_memory.c
> +++ b/mm/huge_memory.c
> @@ -755,7 +755,7 @@ static void insert_pfn_pmd(struct vm_area_struct *vma, unsigned long addr,
>  	spin_unlock(ptl);
>  }
>  
> -int vmf_insert_pfn_pmd(struct vm_area_struct *vma, unsigned long addr,
> +vm_fault_t vmf_insert_pfn_pmd(struct vm_area_struct *vma, unsigned long addr,
>  			pmd_t *pmd, pfn_t pfn, bool write)
>  {
>  	pgprot_t pgprot = vma->vm_page_prot;
> @@ -815,7 +815,7 @@ static void insert_pfn_pud(struct vm_area_struct *vma, unsigned long addr,
>  	spin_unlock(ptl);
>  }
>  
> -int vmf_insert_pfn_pud(struct vm_area_struct *vma, unsigned long addr,
> +vm_fault_t vmf_insert_pfn_pud(struct vm_area_struct *vma, unsigned long addr,
>  			pud_t *pud, pfn_t pfn, bool write)
>  {
>  	pgprot_t pgprot = vma->vm_page_prot;

This isn't very useful unless functions that return the return value of 
these functions, __dev_dax_{pmd,pud}_fault(), recast it as an int.  
__dev_dax_pte_fault() would do the same thing, so it should logically also 
be vm_fault_t, so then you would convert dev_dax_huge_fault() and
dev_dax_fault() as well in the same patch.