mm: avoid taking rmap locks in move_ptes()

During mremap(), the destination VMA is generally placed after the
original vma in rmap traversal order: in move_vma(), we always have
new_pgoff >= vma->vm_pgoff, and as a result new_vma->vm_pgoff >=
vma->vm_pgoff unless vma_merge() merged the new vma with an adjacent one.

When the destination VMA is placed after the original in rmap traversal
order, we can avoid taking the rmap locks in move_ptes().

Essentially, this reintroduces the optimization that had been disabled in
"mm anon rmap: remove anon_vma_moveto_tail".  The difference is that we
don't try to impose the rmap traversal order; instead we just rely on
things being in the desired order in the common case and fall back to
taking locks in the uncommon case.  Also we skip the i_mmap_mutex in
addition to the anon_vma lock: in both cases, the vmas are traversed in
increasing vm_pgoff order with ties resolved in tree insertion order.

Signed-off-by: Michel Lespinasse <walken@google.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Rik van Riel <riel@redhat.com>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Daniel Santos <daniel.santos@pobox.com>
Cc: Hugh Dickins <hughd@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 4 insertions, 2 deletions

diff --git a/include/linux/mm.h b/include/linux/mm.h
index 0e6f9c9f2123..0d5f823ce3fc 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -1060,7 +1060,8 @@ vm_is_stack(struct task_struct *task, struct vm_area_struct *vma, int in_group);
 
 extern unsigned long move_page_tables(struct vm_area_struct *vma,
 		unsigned long old_addr, struct vm_area_struct *new_vma,
-		unsigned long new_addr, unsigned long len);
+		unsigned long new_addr, unsigned long len,
+		bool need_rmap_locks);
 extern unsigned long do_mremap(unsigned long addr,
 			       unsigned long old_len, unsigned long new_len,
 			       unsigned long flags, unsigned long new_addr);
@@ -1410,7 +1411,8 @@ extern void __vma_link_rb(struct mm_struct *, struct vm_area_struct *,
 	struct rb_node **, struct rb_node *);
 extern void unlink_file_vma(struct vm_area_struct *);
 extern struct vm_area_struct *copy_vma(struct vm_area_struct **,
-	unsigned long addr, unsigned long len, pgoff_t pgoff);
+	unsigned long addr, unsigned long len, pgoff_t pgoff,
+	bool *need_rmap_locks);
 extern void exit_mmap(struct mm_struct *);
 
 extern int mm_take_all_locks(struct mm_struct *mm);