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, 7 insertions, 5 deletions

diff --git a/ipc/shm.c b/ipc/shm.c
index 4fa6d8fee730..9f047ba69e62 100644
--- a/ipc/shm.c
+++ b/ipc/shm.c
@@ -967,11 +967,11 @@ long do_shmat(int shmid, char __user *shmaddr, int shmflg, ulong *raddr,
         unsigned long flags;
         unsigned long prot;
         int acc_mode;
-        unsigned long user_addr;
         struct ipc_namespace *ns;
         struct shm_file_data *sfd;
         struct path path;
         fmode_t f_mode;
+        bool populate = false;
 
         err = -EINVAL;
         if (shmid < 0)
@@ -1070,13 +1070,15 @@ long do_shmat(int shmid, char __user *shmaddr, int shmflg, ulong *raddr,
                         goto invalid;
         }
                 
-        user_addr = do_mmap_pgoff(file, addr, size, prot, flags, 0);
-        *raddr = user_addr;
+        addr = do_mmap_pgoff(file, addr, size, prot, flags, 0, &populate);
+        *raddr = addr;
         err = 0;
-        if (IS_ERR_VALUE(user_addr))
-                err = (long)user_addr;
+        if (IS_ERR_VALUE(addr))
+                err = (long)addr;
 invalid:
         up_write(&current->mm->mmap_sem);
+        if (populate)
+                mm_populate(addr, size);
 
 out_fput:
         fput(file);