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

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Date:   Fri, 27 Apr 2018 11:19:09 +0530
From:   Souptick Joarder <jrdr.linux@...il.com>
To:     David Rientjes <rientjes@...gle.com>,
        Matthew Wilcox <willy@...radead.org>
Cc:     Andrew Morton <akpm@...ux-foundation.org>, zi.yan@...rutgers.edu,
        Dan Williams <dan.j.williams@...el.com>,
        kirill.shutemov@...ux.intel.com,
        Ross Zwisler <ross.zwisler@...ux.intel.com>,
        n-horiguchi@...jp.nec.com, Michal Hocko <mhocko@...e.com>,
        shli@...com, linux-kernel@...r.kernel.org,
        Linux-MM <linux-mm@...ck.org>
Subject: Re: [PATCH v2] mm: huge_memory: Change return type to vm_fault_t

On Wed, Apr 25, 2018 at 12:39 PM, David Rientjes <rientjes@...gle.com> wrote:
> 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.

yes, the return value of _dev_dax_{pmd,pud,pte}_fault(), dev_dax_huge_fault(),
dev_dax_fault() is already changed in a separate patch which was reviewed
by Matthew and Ross. Other patch was posted in linux-nvdimm mailing list.