mm: merge populate and nopage into fault (fixes nonlinear)

Nonlinear mappings are (AFAIKS) simply a virtual memory concept that encodes
the virtual address -> file offset differently from linear mappings.

->populate is a layering violation because the filesystem/pagecache code
should need to know anything about the virtual memory mapping.  The hitch here
is that the ->nopage handler didn't pass down enough information (ie.  pgoff).
 But it is more logical to pass pgoff rather than have the ->nopage function
calculate it itself anyway (because that's a similar layering violation).

Having the populate handler install the pte itself is likewise a nasty thing
to be doing.

This patch introduces a new fault handler that replaces ->nopage and
->populate and (later) ->nopfn.  Most of the old mechanism is still in place
so there is a lot of duplication and nice cleanups that can be removed if
everyone switches over.

The rationale for doing this in the first place is that nonlinear mappings are
subject to the pagefault vs invalidate/truncate race too, and it seemed stupid
to duplicate the synchronisation logic rather than just consolidate the two.

After this patch, MAP_NONBLOCK no longer sets up ptes for pages present in
pagecache.  Seems like a fringe functionality anyway.

NOPAGE_REFAULT is removed.  This should be implemented with ->fault, and no
users have hit mainline yet.

[akpm@linux-foundation.org: cleanup]
[randy.dunlap@oracle.com: doc. fixes for readahead]
[akpm@linux-foundation.org: build fix]
Signed-off-by: Nick Piggin <npiggin@suse.de>
Signed-off-by: Randy Dunlap <randy.dunlap@oracle.com>
Cc: Mark Fasheh <mark.fasheh@oracle.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 5 insertions, 4 deletions

diff --git a/ipc/shm.c b/ipc/shm.c
index 242c3f66493..e2d090348b1 100644
--- a/ipc/shm.c
+++ b/ipc/shm.c
@@ -224,13 +224,13 @@ static void shm_close(struct vm_area_struct *vma)
         mutex_unlock(&shm_ids(ns).mutex);
 }
 
-static struct page *shm_nopage(struct vm_area_struct *vma,
-                               unsigned long address, int *type)
+static struct page *shm_fault(struct vm_area_struct *vma,
+                                        struct fault_data *fdata)
 {
         struct file *file = vma->vm_file;
         struct shm_file_data *sfd = shm_file_data(file);
 
-        return sfd->vm_ops->nopage(vma, address, type);
+        return sfd->vm_ops->fault(vma, fdata);
 }
 
 #ifdef CONFIG_NUMA
@@ -269,6 +269,7 @@ static int shm_mmap(struct file * file, struct vm_area_struct * vma)
         if (ret != 0)
                 return ret;
         sfd->vm_ops = vma->vm_ops;
+        BUG_ON(!sfd->vm_ops->fault);
         vma->vm_ops = &shm_vm_ops;
         shm_open(vma);
 
@@ -327,7 +328,7 @@ static const struct file_operations shm_file_operations = {
 static struct vm_operations_struct shm_vm_ops = {
         .open   = shm_open,     /* callback for a new vm-area open */
         .close  = shm_close,    /* callback for when the vm-area is released */
-        .nopage = shm_nopage,
+        .fault  = shm_fault,
 #if defined(CONFIG_NUMA)
         .set_policy = shm_set_policy,
         .get_policy = shm_get_policy,