X-Git-Url: https://err.no/cgi-bin/gitweb.cgi?a=blobdiff_plain;f=mm%2Fmemory.c;h=a596c1172248e56b8fb220408548330ebd1de538;hb=d44ed4f86892e350f4b16a3489b7e7c1a9bb7ead;hp=81d7117aa58b65ec7f93cef8e212a337735ba440;hpb=f33ea7f404e592e4563b12101b7a4d17da6558d7;p=linux-2.6

diff --git a/mm/memory.c b/mm/memory.c
index 81d7117aa5..a596c11722 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -498,6 +498,17 @@ int copy_page_range(struct mm_struct *dst_mm, struct mm_struct *src_mm,
 	unsigned long addr = vma->vm_start;
 	unsigned long end = vma->vm_end;
 
+	/*
+	 * Don't copy ptes where a page fault will fill them correctly.
+	 * Fork becomes much lighter when there are big shared or private
+	 * readonly mappings. The tradeoff is that copy_page_range is more
+	 * efficient than faulting.
+	 */
+	if (!(vma->vm_flags & (VM_HUGETLB|VM_NONLINEAR|VM_RESERVED))) {
+		if (!vma->anon_vma)
+			return 0;
+	}
+
 	if (is_vm_hugetlb_page(vma))
 		return copy_hugetlb_page_range(dst_mm, src_mm, vma);
 
@@ -949,6 +960,8 @@ int get_user_pages(struct task_struct *tsk, struct mm_struct *mm,
 
 			cond_resched_lock(&mm->page_table_lock);
 			while (!(page = follow_page(mm, start, write_access))) {
+				int ret;
+
 				/*
 				 * Shortcut for anonymous pages. We don't want
 				 * to force the creation of pages tables for
@@ -961,16 +974,18 @@ int get_user_pages(struct task_struct *tsk, struct mm_struct *mm,
 					break;
 				}
 				spin_unlock(&mm->page_table_lock);
-				switch (__handle_mm_fault(mm, vma, start,
-							write_access)) {
-				case VM_FAULT_WRITE:
-					/*
-					 * do_wp_page has broken COW when
-					 * necessary, even if maybe_mkwrite
-					 * decided not to set pte_write
-					 */
+				ret = __handle_mm_fault(mm, vma, start, write_access);
+
+				/*
+				 * The VM_FAULT_WRITE bit tells us that do_wp_page has
+				 * broken COW when necessary, even if maybe_mkwrite
+				 * decided not to set pte_write. We can thus safely do
+				 * subsequent page lookups as if they were reads.
+				 */
+				if (ret & VM_FAULT_WRITE)
 					write_access = 0;
-					/* FALLTHRU */
+				
+				switch (ret & ~VM_FAULT_WRITE) {
 				case VM_FAULT_MINOR:
 					tsk->min_flt++;
 					break;