mm: introduce mm_populate() for populating new vmas

When creating new mappings using the MAP_POPULATE / MAP_LOCKED flags (or
with MCL_FUTURE in effect), we want to populate the pages within the
newly created vmas.  This may take a while as we may have to read pages
from disk, so ideally we want to do this outside of the write-locked
mmap_sem region.

This change introduces mm_populate(), which is used to defer populating
such mappings until after the mmap_sem write lock has been released.
This is implemented as a generalization of the former do_mlock_pages(),
which accomplished the same task but was using during mlock() /
mlockall().

Signed-off-by: Michel Lespinasse <walken@google.com>
Reported-by: Andy Lutomirski <luto@amacapital.net>
Acked-by: Rik van Riel <riel@redhat.com>
Tested-by: Andy Lutomirski <luto@amacapital.net>
Cc: Greg Ungerer <gregungerer@westnet.com.au>
Cc: David Howells <dhowells@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 4 insertions, 1 deletions

diff --git a/mm/nommu.c b/mm/nommu.c
index b20db4e22263..7296a5a280e7 100644
--- a/mm/nommu.c
+++ b/mm/nommu.c
@@ -1250,7 +1250,8 @@ unsigned long do_mmap_pgoff(struct file *file,
                             unsigned long len,
                             unsigned long prot,
                             unsigned long flags,
-                            unsigned long pgoff)
+                            unsigned long pgoff,
+                            bool *populate)
 {
         struct vm_area_struct *vma;
         struct vm_region *region;
@@ -1260,6 +1261,8 @@ unsigned long do_mmap_pgoff(struct file *file,
 
         kenter(",%lx,%lx,%lx,%lx,%lx", addr, len, prot, flags, pgoff);
 
+        *populate = false;
+
         /* decide whether we should attempt the mapping, and if so what sort of
          * mapping */
         ret = validate_mmap_request(file, addr, len, prot, flags, pgoff,