[RFC] Simplify users of vma_address_end()

[Matthew Wilcox <willy@xxxxxxxxxxxxx>]

Hi Hugh,

What do you think to this simplification?  Dave dislikes the ?: usage
in this context, and I thought we could usefully put the condition
inside the (inline) function.

I could also go for:

	if (!PageCompound(page))
		return address + PAGE_SIZE;
	VM_BUG_ON_PAGE(PageKsm(page), page);    /* KSM page->index unusable */

in case anyone starts to create compound KSM pages.

diff --git a/mm/internal.h b/mm/internal.h
index c774075b3893..7cd33ee4df32 100644
--- a/mm/internal.h
+++ b/mm/internal.h
@@ -462,13 +462,13 @@ vma_address(struct page *page, struct vm_area_struct *vma)
  * Assumes that vma_address() already returned a good starting address.
  * If page is a compound head, the entire compound page is considered.
  */
-static inline unsigned long
-vma_address_end(struct page *page, struct vm_area_struct *vma)
+static inline unsigned long vma_address_end(struct page *page,
+		unsigned long address, struct vm_area_struct *vma)
 {
 	pgoff_t pgoff;
-	unsigned long address;
 
-	VM_BUG_ON_PAGE(PageKsm(page), page);	/* KSM page->index unusable */
+	if (PageKsm(page) || !PageCompound(page))
+		return address + PAGE_SIZE;
 	pgoff = page_to_pgoff(page) + compound_nr(page);
 	address = vma->vm_start + ((pgoff - vma->vm_pgoff) << PAGE_SHIFT);
 	/* Check for address beyond vma (or wrapped through 0?) */
diff --git a/mm/page_vma_mapped.c b/mm/page_vma_mapped.c
index f7b331081791..fcd7b9ccfb1e 100644
--- a/mm/page_vma_mapped.c
+++ b/mm/page_vma_mapped.c
@@ -181,15 +181,7 @@ bool page_vma_mapped_walk(struct page_vma_mapped_walk *pvmw)
 		return true;
 	}
 
-	/*
-	 * Seek to next pte only makes sense for THP.
-	 * But more important than that optimization, is to filter out
-	 * any PageKsm page: whose page->index misleads vma_address()
-	 * and vma_address_end() to disaster.
-	 */
-	end = PageTransCompound(page) ?
-		vma_address_end(page, pvmw->vma) :
-		pvmw->address + PAGE_SIZE;
+	end = vma_address_end(page, pvmw->address, pvmw->vma);
 	if (pvmw->pte)
 		goto next_pte;
 restart:
diff --git a/mm/rmap.c b/mm/rmap.c
index a531b64d53fa..5d5dc2a60a26 100644
--- a/mm/rmap.c
+++ b/mm/rmap.c
@@ -946,7 +946,7 @@ static bool page_mkclean_one(struct page *page, struct vm_area_struct *vma,
 	 */
 	mmu_notifier_range_init(&range, MMU_NOTIFY_PROTECTION_PAGE,
 				0, vma, vma->vm_mm, address,
-				vma_address_end(page, vma));
+				vma_address_end(page, address, vma));
 	mmu_notifier_invalidate_range_start(&range);
 
 	while (page_vma_mapped_walk(&pvmw)) {
@@ -1453,8 +1453,7 @@ static bool try_to_unmap_one(struct page *page, struct vm_area_struct *vma,
 	 * Note that the page can not be free in this function as call of
 	 * try_to_unmap() must hold a reference on the page.
 	 */
-	range.end = PageKsm(page) ?
-			address + PAGE_SIZE : vma_address_end(page, vma);
+	range.end = vma_address_end(page, address, vma);
 	mmu_notifier_range_init(&range, MMU_NOTIFY_CLEAR, 0, vma, vma->vm_mm,
 				address, range.end);
 	if (PageHuge(page)) {
@@ -1757,8 +1756,7 @@ static bool try_to_migrate_one(struct page *page, struct vm_area_struct *vma,
 	 * Note that the page can not be free in this function as call of
 	 * try_to_unmap() must hold a reference on the page.
 	 */
-	range.end = PageKsm(page) ?
-			address + PAGE_SIZE : vma_address_end(page, vma);
+	range.end = vma_address_end(page, address, vma);
 	mmu_notifier_range_init(&range, MMU_NOTIFY_CLEAR, 0, vma, vma->vm_mm,
 				address, range.end);
 	if (PageHuge(page)) {