Re: [PATCH] hmm: Suppress compilation warnings when CONFIG_HUGETLB_PAGE is not set

[Andrew Morton <akpm@linux-foundation.org>]

On Wed, 22 May 2019 19:51:55 +0000 Jason Gunthorpe <jgg@mellanox.com> wrote:

> gcc reports that several variables are defined but not used.
> 
> For the first hunk CONFIG_HUGETLB_PAGE the entire if block is already
> protected by pud_huge() which is forced to 0. None of the stuff under
> the ifdef causes compilation problems as it is already stubbed out in
> the header files.
> 
> For the second hunk the dummy huge_page_shift macro doesn't touch the
> argument, so just inline the argument.
> 
> ...
>
> --- a/mm/hmm.c
> +++ b/mm/hmm.c
> @@ -797,7 +797,6 @@ static int hmm_vma_walk_pud(pud_t *pudp,
>  			return hmm_vma_walk_hole_(addr, end, fault,
>  						write_fault, walk);
>  
> -#ifdef CONFIG_HUGETLB_PAGE
>  		pfn = pud_pfn(pud) + ((addr & ~PUD_MASK) >> PAGE_SHIFT);
>  		for (i = 0; i < npages; ++i, ++pfn) {
>  			hmm_vma_walk->pgmap = get_dev_pagemap(pfn,
> @@ -813,9 +812,6 @@ static int hmm_vma_walk_pud(pud_t *pudp,
>  		}
>  		hmm_vma_walk->last = end;
>  		return 0;
> -#else
> -		return -EINVAL;
> -#endif
>  	}

Fair enough.

>  	split_huge_pud(walk->vma, pudp, addr);
> @@ -1024,9 +1020,8 @@ long hmm_range_snapshot(struct hmm_range *range)
>  			return -EFAULT;
>  
>  		if (is_vm_hugetlb_page(vma)) {
> -			struct hstate *h = hstate_vma(vma);
> -
> -			if (huge_page_shift(h) != range->page_shift &&
> +			if (huge_page_shift(hstate_vma(vma)) !=
> +				    range->page_shift &&
>  			    range->page_shift != PAGE_SHIFT)
>  				return -EINVAL;

Also fair enough.  But why the heck is huge_page_shift() a macro?  We
keep doing that and it bites so often :(