Re: [PATCH resend v2] /dev/zero: try to align PMD_SIZE for private mapping

[Lorenzo Stoakes]

On Wed, Jul 30, 2025 at 01:49:34PM +0100, Matthew Wilcox wrote:
> On Wed, Jul 30, 2025 at 05:19:05PM +0800, Zhang Qilong wrote:
> > +	if (IS_ENABLED(CONFIG_TRANSPARENT_HUGEPAGE))
> > +		return thp_get_unmapped_area(file, addr, len, pgoff, flags);
> > +
> >  	return mm_get_unmapped_area(current->mm, file, addr, len, pgoff, flags);
>
> I'm sure the build bots will give us a compiler error.
> If CONFIG_TRANSPARENT_HUGEPAGE is not enabled, we get:
> include/linux/huge_mm.h:#define thp_get_unmapped_area   NULL
>
> and we chose that so that various filesystems can unconditionally set
> their .get_unmapped_area method to it.
>
> Which means the cpp will turn this into:
>
> 	if (0)
> 		return NULL(file, addr, len, pgoff, flags);
>
> and the compiler will say:
>
> error: implicit declaration of function ‘NULL’ [-Wimplicit-function-declaration]
>

Yeah I did ask explicitly for #ifdef here :)