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>

2 files changed, 29 insertions, 0 deletions

diff --git a/Documentation/feature-removal-schedule.txt b/Documentation/feature-removal-schedule.txt
index 66c8b4b165c1..716568afdff8 100644
--- a/Documentation/feature-removal-schedule.txt
+++ b/Documentation/feature-removal-schedule.txt
@@ -135,6 +135,33 @@ Who:	Greg Kroah-Hartman <gregkh@suse.de>
 
 ---------------------------
 
+What:   filemap_nopage, filemap_populate
+When:   April 2007
+Why:    These legacy interfaces no longer have any callers in the kernel and
+        any functionality provided can be provided with filemap_fault. The
+        removal schedule is short because they are a big maintainence burden
+        and have some bugs.
+Who:    Nick Piggin <npiggin@suse.de>
+
+---------------------------
+
+What:   vm_ops.populate, install_page
+When:   April 2007
+Why:    These legacy interfaces no longer have any callers in the kernel and
+        any functionality provided can be provided with vm_ops.fault.
+Who:    Nick Piggin <npiggin@suse.de>
+
+---------------------------
+
+What:   vm_ops.nopage
+When:   February 2008, provided in-kernel callers have been converted
+Why:    This interface is replaced by vm_ops.fault, but it has been around
+        forever, is used by a lot of drivers, and doesn't cost much to
+        maintain.
+Who:    Nick Piggin <npiggin@suse.de>
+
+---------------------------
+
 What:   Interrupt only SA_* flags
 When:   September 2007
 Why:    The interrupt related SA_* flags are replaced by IRQF_* to move them
diff --git a/Documentation/filesystems/Locking b/Documentation/filesystems/Locking
index d866551be037..970c8ec1a05b 100644
--- a/Documentation/filesystems/Locking
+++ b/Documentation/filesystems/Locking
@@ -510,12 +510,14 @@ More details about quota locking can be found in fs/dquot.c.
 prototypes:
         void (*open)(struct vm_area_struct*);
         void (*close)(struct vm_area_struct*);
+        struct page *(*fault)(struct vm_area_struct*, struct fault_data *);
         struct page *(*nopage)(struct vm_area_struct*, unsigned long, int *);
 
 locking rules:
                 BKL     mmap_sem
 open:           no      yes
 close:          no      yes
+fault:          no      yes
 nopage:         no      yes
 
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