--- 2.4.19pre7aa2/mm/memory.c.~1~	Fri Apr 26 08:35:08 2002
+++ 2.4.19pre7aa2/mm/memory.c	Fri Apr 26 09:08:33 2002
@@ -422,20 +422,26 @@
 /*
  * Do a quick page-table lookup for a single page. 
  */
-static struct page * follow_page(struct mm_struct *mm, unsigned long address, int write) 
+static struct page * follow_page(struct mm_struct *mm, unsigned long address, int write, int file_backed)
 {
 	pgd_t *pgd;
 	pmd_t *pmd;
 	pte_t *ptep, pte;
+	int none = 1;
 
 	pgd = pgd_offset(mm, address);
-	if (pgd_none(*pgd) || pgd_bad(*pgd))
+	if (pgd_none(*pgd))
 		goto out;
+	if (pgd_bad(*pgd))
+		BUG();
 
 	pmd = pmd_offset(pgd, address);
-	if (pmd_none(*pmd) || pmd_bad(*pmd))
+	if (pmd_none(*pmd))
 		goto out;
+	if (pmd_bad(*pmd))
+		BUG();
 
+	none = 0;
 	ptep = pte_offset_atomic(pmd, address);
 
 	pte = *ptep;
@@ -445,8 +451,22 @@
 		    (pte_write(pte) && pte_dirty(pte)))
 			return pte_page(pte);
 	}
+	if (pte_none(pte))
+		none = 1;
 
 out:
+	if (!write && none && !file_backed)
+		/*
+		 * Optimization to avoid building the pagetable layout
+		 * during core dumps of unmapped areas where we only
+		 * want to seek and to create an hole in the dump:
+		 * if 1) the pte is null, 2) the file isn't filebacked and
+		 * 3) this is a read, then we can let the reader to read
+		 * from the zero page (the coredump will also notice
+		 * this is the magic zeropage and it will seek accordingly).
+		 */
+		return ZERO_PAGE(address);
+
 	return 0;
 }
 
@@ -495,7 +515,7 @@
 		spin_lock(&mm->page_table_lock);
 		do {
 			struct page *map;
-			while (!(map = follow_page(mm, start, write))) {
+			while (!(map = follow_page(mm, start, write, vma->vm_file != 0))) {
 				spin_unlock(&mm->page_table_lock);
 				switch (handle_mm_fault(mm, vma, start, write)) {
 				case 1: