mm: kill vma flag VM_INSERTPAGE

Merge VM_INSERTPAGE into VM_MIXEDMAP. VM_MIXEDMAP VMA can mix pure-pfn
ptes, special ptes and normal ptes.

Now copy_page_range() always copies VM_MIXEDMAP VMA on fork like
VM_PFNMAP. If driver populates whole VMA at mmap() it probably not
expects page-faults.

This patch removes special check from vma_wants_writenotify() which
disables pages write tracking for VMA populated via vm_instert_page().
BDI below mapped file should not use dirty-accounting, moreover
do_wp_page() can handle this.

vm_insert_page() still marks vma after first usage. Usually it is called
from f_op->mmap() handler under mm->mmap_sem write-lock, so it able to
change vma->vm_flags. Caller must set VM_MIXEDMAP at mmap time if it
wants to call this function from other places, for example from page-fault
handler.

Signed-off-by: Konstantin Khlebnikov <[e-mail]>
Cc: Alexander Viro <[e-mail]>
Cc: Carsten Otte <[e-mail]>
Cc: Chris Metcalf <[e-mail]>
Cc: Cyrill Gorcunov <[e-mail]>
Cc: Eric Paris <[e-mail]>
Cc: H. Peter Anvin <[e-mail]>
Cc: Hugh Dickins <[e-mail]>
Cc: Ingo Molnar <[e-mail]>
Cc: James Morris <[e-mail]>
Cc: Jason Baron <[e-mail]>
Cc: Kentaro Takeda <[e-mail]>
Cc: Matt Helsley <[e-mail]>
Cc: Nick Piggin <[e-mail]>
Cc: Oleg Nesterov <[e-mail]>
Cc: Peter Zijlstra <[e-mail]>
Cc: Robert Richter <[e-mail]>
Cc: Suresh Siddha <[e-mail]>
Cc: Tetsuo Handa <[e-mail]>
Cc: Venkatesh Pallipadi <[e-mail]>
Acked-by: Linus Torvalds <[e-mail]>
Signed-off-by: Andrew Morton <[e-mail]>
Signed-off-by: Linus Torvalds <[e-mail]>

include/linux/mm.h

···
 #define VM_HUGETLB	0x00400000	/* Huge TLB Page VM */
 #define VM_NONLINEAR	0x00800000	/* Is non-linear (remap_file_pages) */
 #define VM_ARCH_1	0x01000000	/* Architecture-specific flag */
-#define VM_INSERTPAGE	0x02000000	/* The vma has had "vm_insert_page()" done on it */
 #define VM_NODUMP	0x04000000	/* Do not include in the core dump */
 
 #define VM_CAN_NONLINEAR 0x08000000	/* Has ->fault & does nonlinear pages */

mm/huge_memory.c

···
 	return ret;
 }
 
-#define VM_NO_THP (VM_SPECIAL|VM_INSERTPAGE|VM_MIXEDMAP| \
-		   VM_HUGETLB|VM_SHARED|VM_MAYSHARE)
+#define VM_NO_THP (VM_SPECIAL|VM_MIXEDMAP|VM_HUGETLB|VM_SHARED|VM_MAYSHARE)
 
 int hugepage_madvise(struct vm_area_struct *vma,
 		     unsigned long *vm_flags, int advice)

mm/ksm.c

···
 		 */
 		if (*vm_flags & (VM_MERGEABLE | VM_SHARED  | VM_MAYSHARE   |
 				 VM_PFNMAP    | VM_IO      | VM_DONTEXPAND |
-				 VM_RESERVED  | VM_HUGETLB | VM_INSERTPAGE |
+				 VM_RESERVED  | VM_HUGETLB |
 				 VM_NONLINEAR | VM_MIXEDMAP))
 			return 0;		/* just ignore the advice */
 

mm/memory.c

···
 	 * readonly mappings. The tradeoff is that copy_page_range is more
 	 * efficient than faulting.
 	 */
-	if (!(vma->vm_flags & (VM_HUGETLB|VM_NONLINEAR|VM_PFNMAP|VM_INSERTPAGE))) {
+	if (!(vma->vm_flags & (VM_HUGETLB | VM_NONLINEAR |
+			       VM_PFNMAP | VM_MIXEDMAP))) {
 		if (!vma->anon_vma)
 			return 0;
 	}
···
  * ask for a shared writable mapping!
  *
  * The page does not need to be reserved.
+ *
+ * Usually this function is called from f_op->mmap() handler
+ * under mm->mmap_sem write-lock, so it can change vma->vm_flags.
+ * Caller must set VM_MIXEDMAP on vma if it wants to call this
+ * function from other places, for example from page-fault handler.
  */
 int vm_insert_page(struct vm_area_struct *vma, unsigned long addr,
 			struct page *page)
···
 		return -EFAULT;
 	if (!page_count(page))
 		return -EINVAL;
-	vma->vm_flags |= VM_INSERTPAGE;
+	if (!(vma->vm_flags & VM_MIXEDMAP)) {
+		BUG_ON(down_read_trylock(&vma->vm_mm->mmap_sem));
+		BUG_ON(vma->vm_flags & VM_PFNMAP);
+		vma->vm_flags |= VM_MIXEDMAP;
+	}
 	return insert_page(vma, addr, page, vma->vm_page_prot);
 }
 EXPORT_SYMBOL(vm_insert_page);

mm/mmap.c

···
 		return 0;
 
 	/* Specialty mapping? */
-	if (vm_flags & (VM_PFNMAP|VM_INSERTPAGE))
+	if (vm_flags & VM_PFNMAP)
 		return 0;
 
 	/* Can the mapping track the dirty pages? */