From: Olaf Kirch <okir@suse.de>
Subject: Do not call shrink_dcache_sb when remounting procfs etc
Patch-mainline: Not yet
References: 165672
Patch-mainline: not yet

Avoid calls to shrink_dcache_sb when mounting a file system that
uses get_sb_single. shrink_dcache_sb is costly. On large ia64
systems, this will keep the dcache lock for > 60 seconds at
a stretch.

Signed-off-by: Olaf Kirch <okir@suse.de>

 fs/super.c |   36 +++++++++++++++++++++++-------------
 1 file changed, 23 insertions(+), 13 deletions(-)

--- a/fs/super.c
+++ b/fs/super.c
@@ -521,16 +521,10 @@ rescan:
 	return NULL;
 }
 
-/**
- *	do_remount_sb - asks filesystem to change mount options.
- *	@sb:	superblock in question
- *	@flags:	numeric part of options
- *	@data:	the rest of options
- *      @force: whether or not to force the change
- *
- *	Alters the mount options of a mounted file system.
- */
-int do_remount_sb(struct super_block *sb, int flags, void *data, int force)
+#define REMOUNT_FORCE		1
+#define REMOUNT_SHRINK_DCACHE	2
+
+static int __do_remount_sb(struct super_block *sb, int flags, void *data, int rflags)
 {
 	int retval;
 	int remount_ro;
@@ -545,7 +539,8 @@ int do_remount_sb(struct super_block *sb
 
 	if (flags & MS_RDONLY)
 		acct_auto_close(sb);
-	shrink_dcache_sb(sb);
+	if (rflags & REMOUNT_SHRINK_DCACHE)
+		shrink_dcache_sb(sb);
 	sync_filesystem(sb);
 
 	remount_ro = (flags & MS_RDONLY) && !(sb->s_flags & MS_RDONLY);
@@ -553,7 +548,7 @@ int do_remount_sb(struct super_block *sb
 	/* If we are remounting RDONLY and current sb is read/write,
 	   make sure there are no rw files opened */
 	if (remount_ro) {
-		if (force)
+		if (rflags & REMOUNT_FORCE)
 			mark_files_ro(sb);
 		else if (!fs_may_remount_ro(sb))
 			return -EBUSY;
@@ -579,6 +574,21 @@ int do_remount_sb(struct super_block *sb
 	return 0;
 }
 
+/**
+ *	do_remount_sb - asks filesystem to change mount options.
+ *	@sb:	superblock in question
+ *	@flags:	numeric part of options
+ *	@data:	the rest of options
+ *      @force: whether or not to force the change
+ *
+ *	Alters the mount options of a mounted file system.
+ */
+int do_remount_sb(struct super_block *sb, int flags, void *data, int force)
+{
+	return __do_remount_sb(sb, flags, data,
+			REMOUNT_SHRINK_DCACHE|(force? REMOUNT_FORCE : 0));
+}
+
 static void do_emergency_remount(struct work_struct *work)
 {
 	struct super_block *sb, *p = NULL;
@@ -888,7 +898,7 @@ int get_sb_single(struct file_system_typ
 		}
 		s->s_flags |= MS_ACTIVE;
 	} else {
-		do_remount_sb(s, flags, data, 0);
+		__do_remount_sb(s, flags, data, 0);
 	}
 	return dget(s->s_root);
 }