reduce large do_mount stack usage with noinlines

do_mount() uses a whopping 616 bytes of stack on x86_64 in 2.6.24-mm1,
largely thanks to gcc inlining the various helper functions.

noinlining these can slim it down a lot; on my box this patch gets it down
to 168, which is mostly the struct nameidata nd; left on the stack.

These functions are called only as do_mount() helpers; none of them should
be in any path that would see a performance benefit from inlining...

Signed-off-by: Eric Sandeen <sandeen@redhat.com>
Cc: Arjan van de Ven <arjan@infradead.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 13 insertions, 5 deletions

diff --git a/fs/namespace.c b/fs/namespace.c
index db51ddc9b671..63ced21c12dc 100644
--- a/fs/namespace.c
+++ b/fs/namespace.c
@@ -936,8 +936,9 @@ out_unlock:
 
 /*
  * recursively change the type of the mountpoint.
+ * noinline this do_mount helper to save do_mount stack space.
  */
-static int do_change_type(struct nameidata *nd, int flag)
+static noinline int do_change_type(struct nameidata *nd, int flag)
 {
         struct vfsmount *m, *mnt = nd->mnt;
         int recurse = flag & MS_REC;
@@ -960,8 +961,10 @@ static int do_change_type(struct nameidata *nd, int flag)
 
 /*
  * do loopback mount.
+ * noinline this do_mount helper to save do_mount stack space.
  */
-static int do_loopback(struct nameidata *nd, char *old_name, int recurse)
+static noinline int do_loopback(struct nameidata *nd, char *old_name,
+                                int recurse)
 {
         struct nameidata old_nd;
         struct vfsmount *mnt = NULL;
@@ -1010,8 +1013,9 @@ out:
  * change filesystem flags. dir should be a physical root of filesystem.
  * If you've mounted a non-root directory somewhere and want to do remount
  * on it - tough luck.
+ * noinline this do_mount helper to save do_mount stack space.
  */
-static int do_remount(struct nameidata *nd, int flags, int mnt_flags,
+static noinline int do_remount(struct nameidata *nd, int flags, int mnt_flags,
                       void *data)
 {
         int err;
@@ -1046,7 +1050,10 @@ static inline int tree_contains_unbindable(struct vfsmount *mnt)
         return 0;
 }
 
-static int do_move_mount(struct nameidata *nd, char *old_name)
+/*
+ * noinline this do_mount helper to save do_mount stack space.
+ */
+static noinline int do_move_mount(struct nameidata *nd, char *old_name)
 {
         struct nameidata old_nd, parent_nd;
         struct vfsmount *p;
@@ -1121,8 +1128,9 @@ out:
 /*
  * create a new mount for userspace and request it to be added into the
  * namespace's tree
+ * noinline this do_mount helper to save do_mount stack space.
  */
-static int do_new_mount(struct nameidata *nd, char *type, int flags,
+static noinline int do_new_mount(struct nameidata *nd, char *type, int flags,
                         int mnt_flags, char *name, void *data)
 {
         struct vfsmount *mnt;