linux-kernel - Re: [PATCH v2 1/1] mm/hmm: Move pmd_to_hmm_pfn

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Message-ID: <wcaeymjmxwdm6gwlpwyklgq4hqzj4bheml3pe7ri7mc7jbjf7n@yjtixgld2ojm>
Date: Fri, 11 Jul 2025 09:35:49 +1000
From: Alistair Popple <apopple@...dia.com>
To: Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
Cc: Leon Romanovsky <leon@...nel.org>, linux-mm@...ck.org, 
	linux-kernel@...r.kernel.org, llvm@...ts.linux.dev, 
	Jérôme Glisse <jglisse@...hat.com>, Andrew Morton <akpm@...ux-foundation.org>, 
	Nathan Chancellor <nathan@...nel.org>, Nick Desaulniers <nick.desaulniers+lkml@...il.com>, 
	Bill Wendling <morbo@...gle.com>, Justin Stitt <justinstitt@...gle.com>
Subject: Re: [PATCH v2 1/1] mm/hmm: Move pmd_to_hmm_pfn_flags() to the
 respective #ifdeffery

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@...dia.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@...ux.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
> 
>