[PATCH v2 1/1] mm/hmm: Move pmd_to_hmm_pfn_flags() to the respective #ifdeffery

[PATCH v2 1/1] mm/hmm: Move pmd_to_hmm_pfn_flags() to the respective #ifdeffery

[Andy Shevchenko]

When pmd_to_hmm_pfn_flags() is unused, it prevents kernel builds with clang,
`make W=1` and CONFIG_TRANSPARENT_HUGEPAGE=n:

  mm/hmm.c:186:29: warning: unused function 'pmd_to_hmm_pfn_flags' [-Wunused-function]

Fix this by moving the function to the respective existing ifdeffery
for its the only user.

See also:

  6863f5643dd7 ("kbuild: allow Clang to find unused static inline functions for W=1 build")

Fixes: 9d3973d60f0a ("mm/hmm: cleanup the hmm_vma_handle_pmd stub")
Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
---

v2: fixed Subject prefix

 mm/hmm.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/mm/hmm.c b/mm/hmm.c
index e8b26aa838b9..015ab243f081 100644
--- a/mm/hmm.c
+++ b/mm/hmm.c
@@ -183,6 +183,7 @@ static inline unsigned long hmm_pfn_flags_order(unsigned long order)
 	return order << HMM_PFN_ORDER_SHIFT;
 }
 
+#ifdef CONFIG_TRANSPARENT_HUGEPAGE
 static inline unsigned long pmd_to_hmm_pfn_flags(struct hmm_range *range,
 						 pmd_t pmd)
 {
@@ -193,7 +194,6 @@ static inline unsigned long pmd_to_hmm_pfn_flags(struct hmm_range *range,
 	       hmm_pfn_flags_order(PMD_SHIFT - PAGE_SHIFT);
 }
 
-#ifdef CONFIG_TRANSPARENT_HUGEPAGE
 static int hmm_vma_handle_pmd(struct mm_walk *walk, unsigned long addr,
 			      unsigned long end, unsigned long hmm_pfns[],
 			      pmd_t pmd)
-- 
2.47.2

Re: [PATCH v2 1/1] mm/hmm: Move pmd_to_hmm_pfn_flags() to the respective #ifdeffery

[Leon Romanovsky]

On Thu, Jul 10, 2025 at 11:23:53AM +0300, Andy Shevchenko wrote:
> When pmd_to_hmm_pfn_flags() is unused, it prevents kernel builds with clang,
> `make W=1` and CONFIG_TRANSPARENT_HUGEPAGE=n:
> 
>   mm/hmm.c:186:29: warning: unused function 'pmd_to_hmm_pfn_flags' [-Wunused-function]
> 
> Fix this by moving the function to the respective existing ifdeffery
> for its the only user.
> 
> See also:
> 
>   6863f5643dd7 ("kbuild: allow Clang to find unused static inline functions for W=1 build")
> 
> Fixes: 9d3973d60f0a ("mm/hmm: cleanup the hmm_vma_handle_pmd stub")
> Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
> ---
> 

Thanks,
Reviewed-by: Leon Romanovsky <leonro@nvidia.com>

Re: [PATCH v2 1/1] mm/hmm: Move pmd_to_hmm_pfn_flags() to the respective #ifdeffery

[Alistair Popple]

Shouldn't the Fixes tag be for the commit that introduced the #ifdeffery in the
first place? Ie: 992de9a8b751 ("mm/hmm: allow to mirror vma of a file on a DAX
backed filesystem")

As far as I can tell that is what would have introduced the warning. Other than
that it looks good though so feel free to add:

Reviewed-by: Alistair Popple <apopple@nvidia.com>

On Thu, Jul 10, 2025 at 11:23:53AM +0300, Andy Shevchenko wrote:
> When pmd_to_hmm_pfn_flags() is unused, it prevents kernel builds with clang,
> `make W=1` and CONFIG_TRANSPARENT_HUGEPAGE=n:
> 
>   mm/hmm.c:186:29: warning: unused function 'pmd_to_hmm_pfn_flags' [-Wunused-function]
> 
> Fix this by moving the function to the respective existing ifdeffery
> for its the only user.
> 
> See also:
> 
>   6863f5643dd7 ("kbuild: allow Clang to find unused static inline functions for W=1 build")
> 
> Fixes: 9d3973d60f0a ("mm/hmm: cleanup the hmm_vma_handle_pmd stub")
> Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
> ---
> 
> v2: fixed Subject prefix
> 
>  mm/hmm.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/mm/hmm.c b/mm/hmm.c
> index e8b26aa838b9..015ab243f081 100644
> --- a/mm/hmm.c
> +++ b/mm/hmm.c
> @@ -183,6 +183,7 @@ static inline unsigned long hmm_pfn_flags_order(unsigned long order)
>  	return order << HMM_PFN_ORDER_SHIFT;
>  }
>  
> +#ifdef CONFIG_TRANSPARENT_HUGEPAGE
>  static inline unsigned long pmd_to_hmm_pfn_flags(struct hmm_range *range,
>  						 pmd_t pmd)
>  {
> @@ -193,7 +194,6 @@ static inline unsigned long pmd_to_hmm_pfn_flags(struct hmm_range *range,
>  	       hmm_pfn_flags_order(PMD_SHIFT - PAGE_SHIFT);
>  }
>  
> -#ifdef CONFIG_TRANSPARENT_HUGEPAGE
>  static int hmm_vma_handle_pmd(struct mm_walk *walk, unsigned long addr,
>  			      unsigned long end, unsigned long hmm_pfns[],
>  			      pmd_t pmd)
> -- 
> 2.47.2
> 
> 

Re: [PATCH v2 1/1] mm/hmm: Move pmd_to_hmm_pfn_flags() to the respective #ifdeffery

[Andy Shevchenko]

On Fri, Jul 11, 2025 at 09:35:49AM +1000, Alistair Popple wrote:
> Shouldn't the Fixes tag be for the commit that introduced the #ifdeffery in the
> first place? Ie: 992de9a8b751 ("mm/hmm: allow to mirror vma of a file on a DAX
> backed filesystem")

Looks indeed better, I was lost in the maze of the history of mm/hmm.c changes.

Fixes: 992de9a8b751 ("mm/hmm: allow to mirror vma of a file on a DAX backed filesystem")

The problem is that backporting to that, if needed, requires a bit of adaptation.
Nevertheless, I added it above, and we actually can have two Fixes tags to make
backporting easier for those (we don't have LTS kernels older that the second
commit anyway),

Andrew, can you add the above tag as well?

> As far as I can tell that is what would have introduced the warning. Other than
> that it looks good though so feel free to add:
> 
> Reviewed-by: Alistair Popple <apopple@nvidia.com>

Thank you for the review!

-- 
With Best Regards,
Andy Shevchenko