linux-kernel - [PATCH] reduce large do_mount stack usage with noinlines

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Date:	Wed, 06 Feb 2008 16:13:58 -0600
From:	Eric Sandeen <sandeen@...hat.com>
To:	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
CC:	Andrew Morton <akpm@...l.org>
Subject: [PATCH] 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@...hat.com>
---

Index: linux-2.6.24-mm1/fs/namespace.c
===================================================================
--- linux-2.6.24-mm1.orig/fs/namespace.c
+++ linux-2.6.24-mm1/fs/namespace.c
@@ -1296,7 +1296,7 @@ out_unlock:
 /*
  * recursively change the type of the mountpoint.
  */
-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->path.mnt;
 	int recurse = flag & MS_REC;
@@ -1320,7 +1320,7 @@ static int do_change_type(struct nameida
 /*
  * do loopback mount.
  */
-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;
@@ -1387,7 +1387,7 @@ static int change_mount_flags(struct vfs
  * If you've mounted a non-root directory somewhere and want to do remount
  * on it - tough luck.
  */
-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;
@@ -1425,7 +1425,7 @@ static inline int tree_contains_unbindab
 	return 0;
 }
 
-static int do_move_mount(struct nameidata *nd, char *old_name)
+static noinline int do_move_mount(struct nameidata *nd, char *old_name)
 {
 	struct nameidata old_nd, parent_nd;
 	struct vfsmount *p;
@@ -1505,7 +1505,7 @@ out:
  * create a new mount for userspace and request it to be added into the
  * namespace's tree
  */
-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;

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