On Thu, Dec 08, 2016 at 01:50:11PM +0300, Kirill A. Shutemov wrote:
> On Wed, Dec 07, 2016 at 11:38:33PM -0500, Jérémy Lefaure wrote:
> > When CONFIG_TRANSPARENT_HUGEPAGE is disabled, split_huge_pmd is a no-op
> > stub. In such case, vma is unused and a compiler raises a warning:
> >
> > arch/x86/kernel/vm86_32.c: In function ‘mark_screen_rdonly’:
> > arch/x86/kernel/vm86_32.c:180:26: warning: unused variable ‘vma’
> > [-Wunused-variable]
> > struct vm_area_struct *vma = find_vma(mm, 0xA0000);
> > ^~~
> > Adding __maybe_unused in the vma declaration fixes this warning.
>
> Hm. pmd_trans_huge() is zero if CONFIG_TRANSPARENT_HUGEPAGE is not set.
> Compiler should get rid of whole block of code under the 'if'.
>
> Could you share your kernel config which triggers the warning?
> And what compiler do you use?
Okay, I see the problem. It still doesn't make sense. Why would compiler
check for unused warnings before dropping unused code.
What about something like this, instead:
diff --git a/include/linux/huge_mm.h b/include/linux/huge_mm.h
index 6f14de45b5ce..b538452a127e 100644
--- a/include/linux/huge_mm.h
+++ b/include/linux/huge_mm.h
@@ -180,7 +180,7 @@ static inline int split_huge_page(struct page *page)
}
static inline void deferred_split_huge_page(struct page *page) {}
#define split_huge_pmd(__vma, __pmd, __address) \
- do { } while (0)
+ do { (void)__vma; } while (0)
static inline void split_huge_pmd_address(struct vm_area_struct *vma,
unsigned long address, bool freeze, struct page *page) {}
--
Kirill A. Shutemov
