Re: [PATCH v4 02/12] device-dax: Cleanup vm_fault de-reference chains

[Laurent Dufour <ldufour@linux.vnet.ibm.com>]

On 09/06/2018 01:50, Dan Williams wrote:
> Define a local 'vma' variable rather than repetitively de-referencing
> the passed in 'struct vm_fault *' instance.

Hi Dan,

Why is this needed ?

I can't see the real benefit, having the vma deferenced from the vm_fault
structure is not obfuscating the code and it eases to follow the use of vmf->vma.

Am I missing something ?

Cheers,
Laurent.

> 
> Signed-off-by: Dan Williams <dan.j.williams@intel.com>
> ---
>  drivers/dax/device.c |   30 ++++++++++++++++--------------
>  1 file changed, 16 insertions(+), 14 deletions(-)
> 
> diff --git a/drivers/dax/device.c b/drivers/dax/device.c
> index d44d98c54d0f..686de08e120b 100644
> --- a/drivers/dax/device.c
> +++ b/drivers/dax/device.c
> @@ -247,13 +247,14 @@ __weak phys_addr_t dax_pgoff_to_phys(struct dev_dax *dev_dax, pgoff_t pgoff,
>  static vm_fault_t __dev_dax_pte_fault(struct dev_dax *dev_dax,
>  				struct vm_fault *vmf)
>  {
> +	struct vm_area_struct *vma = vmf->vma;
>  	struct device *dev = &dev_dax->dev;
>  	struct dax_region *dax_region;
>  	phys_addr_t phys;
>  	pfn_t pfn;
>  	unsigned int fault_size = PAGE_SIZE;
> 
> -	if (check_vma(dev_dax, vmf->vma, __func__))
> +	if (check_vma(dev_dax, vma, __func__))
>  		return VM_FAULT_SIGBUS;
> 
>  	dax_region = dev_dax->region;
> @@ -274,13 +275,14 @@ static vm_fault_t __dev_dax_pte_fault(struct dev_dax *dev_dax,
> 
>  	pfn = phys_to_pfn_t(phys, dax_region->pfn_flags);
> 
> -	return vmf_insert_mixed(vmf->vma, vmf->address, pfn);
> +	return vmf_insert_mixed(vma, vmf->address, pfn);
>  }
> 
>  static vm_fault_t __dev_dax_pmd_fault(struct dev_dax *dev_dax,
>  				struct vm_fault *vmf)
>  {
>  	unsigned long pmd_addr = vmf->address & PMD_MASK;
> +	struct vm_area_struct *vma = vmf->vma;
>  	struct device *dev = &dev_dax->dev;
>  	struct dax_region *dax_region;
>  	phys_addr_t phys;
> @@ -288,7 +290,7 @@ static vm_fault_t __dev_dax_pmd_fault(struct dev_dax *dev_dax,
>  	pfn_t pfn;
>  	unsigned int fault_size = PMD_SIZE;
> 
> -	if (check_vma(dev_dax, vmf->vma, __func__))
> +	if (check_vma(dev_dax, vma, __func__))
>  		return VM_FAULT_SIGBUS;
> 
>  	dax_region = dev_dax->region;
> @@ -310,11 +312,10 @@ static vm_fault_t __dev_dax_pmd_fault(struct dev_dax *dev_dax,
>  		return VM_FAULT_FALLBACK;
> 
>  	/* if we are outside of the VMA */
> -	if (pmd_addr < vmf->vma->vm_start ||
> -			(pmd_addr + PMD_SIZE) > vmf->vma->vm_end)
> +	if (pmd_addr < vma->vm_start || (pmd_addr + PMD_SIZE) > vma->vm_end)
>  		return VM_FAULT_SIGBUS;
> 
> -	pgoff = linear_page_index(vmf->vma, pmd_addr);
> +	pgoff = linear_page_index(vma, pmd_addr);
>  	phys = dax_pgoff_to_phys(dev_dax, pgoff, PMD_SIZE);
>  	if (phys == -1) {
>  		dev_dbg(dev, "pgoff_to_phys(%#lx) failed\n", pgoff);
> @@ -323,7 +324,7 @@ static vm_fault_t __dev_dax_pmd_fault(struct dev_dax *dev_dax,
> 
>  	pfn = phys_to_pfn_t(phys, dax_region->pfn_flags);
> 
> -	return vmf_insert_pfn_pmd(vmf->vma, vmf->address, vmf->pmd, pfn,
> +	return vmf_insert_pfn_pmd(vma, vmf->address, vmf->pmd, pfn,
>  			vmf->flags & FAULT_FLAG_WRITE);
>  }
> 
> @@ -332,6 +333,7 @@ static vm_fault_t __dev_dax_pud_fault(struct dev_dax *dev_dax,
>  				struct vm_fault *vmf)
>  {
>  	unsigned long pud_addr = vmf->address & PUD_MASK;
> +	struct vm_area_struct *vma = vmf->vma;
>  	struct device *dev = &dev_dax->dev;
>  	struct dax_region *dax_region;
>  	phys_addr_t phys;
> @@ -340,7 +342,7 @@ static vm_fault_t __dev_dax_pud_fault(struct dev_dax *dev_dax,
>  	unsigned int fault_size = PUD_SIZE;
> 
> 
> -	if (check_vma(dev_dax, vmf->vma, __func__))
> +	if (check_vma(dev_dax, vma, __func__))
>  		return VM_FAULT_SIGBUS;
> 
>  	dax_region = dev_dax->region;
> @@ -362,11 +364,10 @@ static vm_fault_t __dev_dax_pud_fault(struct dev_dax *dev_dax,
>  		return VM_FAULT_FALLBACK;
> 
>  	/* if we are outside of the VMA */
> -	if (pud_addr < vmf->vma->vm_start ||
> -			(pud_addr + PUD_SIZE) > vmf->vma->vm_end)
> +	if (pud_addr < vma->vm_start || (pud_addr + PUD_SIZE) > vma->vm_end)
>  		return VM_FAULT_SIGBUS;
> 
> -	pgoff = linear_page_index(vmf->vma, pud_addr);
> +	pgoff = linear_page_index(vma, pud_addr);
>  	phys = dax_pgoff_to_phys(dev_dax, pgoff, PUD_SIZE);
>  	if (phys == -1) {
>  		dev_dbg(dev, "pgoff_to_phys(%#lx) failed\n", pgoff);
> @@ -375,7 +376,7 @@ static vm_fault_t __dev_dax_pud_fault(struct dev_dax *dev_dax,
> 
>  	pfn = phys_to_pfn_t(phys, dax_region->pfn_flags);
> 
> -	return vmf_insert_pfn_pud(vmf->vma, vmf->address, vmf->pud, pfn,
> +	return vmf_insert_pfn_pud(vma, vmf->address, vmf->pud, pfn,
>  			vmf->flags & FAULT_FLAG_WRITE);
>  }
>  #else
> @@ -390,12 +391,13 @@ static vm_fault_t dev_dax_huge_fault(struct vm_fault *vmf,
>  		enum page_entry_size pe_size)
>  {
>  	int rc, id;
> -	struct file *filp = vmf->vma->vm_file;
> +	struct vm_area_struct *vma = vmf->vma;
> +	struct file *filp = vma->vm_file;
>  	struct dev_dax *dev_dax = filp->private_data;
> 
>  	dev_dbg(&dev_dax->dev, "%s: %s (%#lx - %#lx) size = %d\n", current->comm,
>  			(vmf->flags & FAULT_FLAG_WRITE) ? "write" : "read",
> -			vmf->vma->vm_start, vmf->vma->vm_end, pe_size);
> +			vma->vm_start, vma->vm_end, pe_size);
> 
>  	id = dax_read_lock();
>  	switch (pe_size) {
>