Re: [PATCH v2] hugetlb: simplify hugetlb handling in follow_page_mask

On 09/05/22 06:34, Christophe Leroy wrote:

Le 02/09/2022 à 21:03, Mike Kravetz a écrit :

quoted

diff --git a/include/linux/hugetlb.h b/include/linux/hugetlb.h
index fe4944f89d34..275e554dd365 100644
--- a/include/linux/hugetlb.h
+++ b/include/linux/hugetlb.h

@@ -264,6 +255,13 @@ static inline void adjust_range_if_pmd_sharing_possible(
  {
  }
  
+static inline struct page *hugetlb_follow_page_mask(struct vm_area_struct *vma,
+				unsigned long address, unsigned int flags)
+{
+	WARN_ON_ONCE(1); /* should never be called if !CONFIG_HUGETLB_PAGE*/
+	return ERR_PTR(-EINVAL);

This function is called only when is_vm_hugetlb_page() is true.

When !CONFIG_HUGETLB_PAGE is_vm_hugetlb_page() always returns false, so 
the call to hugetlb_follow_page_mask() should never be compiled in.

Use BUILD_BUG() to catch it at buildtime.

Yes.  My bad as David suggested this previously.
How about we just leave out the function in the !CONFIG_HUGETLB_PAGE case?
We will get build errors without the need for a BUILD_BUG().

quoted

+}
+
  static inline long follow_hugetlb_page(struct mm_struct *mm,
  			struct vm_area_struct *vma, struct page **pages,
  			struct vm_area_struct **vmas, unsigned long *position,

-- 
Mike Kravetz