hugetlb: add MAP_HUGETLB for mmaping pseudo-anonymous huge page regions

Add a flag for mmap that will be used to request a huge page region that
will look like anonymous memory to userspace.  This is accomplished by
using a file on the internal vfsmount.  MAP_HUGETLB is a modifier of
MAP_ANONYMOUS and so must be specified with it.  The region will behave
the same as a MAP_ANONYMOUS region using small pages.

[akpm@linux-foundation.org: fix arch definitions of MAP_HUGETLB]
Signed-off-by: Eric B Munson <ebmunson@us.ibm.com>
Acked-by: David Rientjes <rientjes@google.com>
Cc: Mel Gorman <mel@csn.ul.ie>
Cc: Adam Litke <agl@us.ibm.com>
Cc: David Gibson <david@gibson.dropbear.id.au>
Cc: Lee Schermerhorn <lee.schermerhorn@hp.com>
Cc: Nick Piggin <nickpiggin@yahoo.com.au>
Cc: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Cc: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 18 insertions, 0 deletions

diff --git a/mm/mmap.c b/mm/mmap.c
index 1aeef6625e6a..21d4029a07b3 100644
--- a/mm/mmap.c
+++ b/mm/mmap.c
@@ -949,6 +949,24 @@ unsigned long do_mmap_pgoff(struct file *file, unsigned long addr,
         if (mm->map_count > sysctl_max_map_count)
                 return -ENOMEM;
 
+        if (flags & MAP_HUGETLB) {
+                struct user_struct *user = NULL;
+                if (file)
+                        return -EINVAL;
+
+                /*
+                 * VM_NORESERVE is used because the reservations will be
+                 * taken when vm_ops->mmap() is called
+                 * A dummy user value is used because we are not locking
+                 * memory so no accounting is necessary
+                 */
+                len = ALIGN(len, huge_page_size(&default_hstate));
+                file = hugetlb_file_setup(HUGETLB_ANON_FILE, len, VM_NORESERVE,
+                                                &user, HUGETLB_ANONHUGE_INODE);
+                if (IS_ERR(file))
+                        return PTR_ERR(file);
+        }
+
         /* Obtain the address to map to. we verify (or select) it and ensure
          * that it represents a valid section of the address space.
          */