From 96029c4e09ccbd73a6d0ed2b29e80bf2586ad7ef Mon Sep 17 00:00:00 2001 From: "npiggin@suse.de" Date: Sun, 26 Apr 2009 20:25:55 +1000 Subject: fs: introduce mnt_clone_write This patch speeds up lmbench lat_mmap test by about another 2% after the first patch. Before: avg = 462.286 std = 5.46106 After: avg = 453.12 std = 9.58257 (50 runs of each, stddev gives a reasonable confidence) It does this by introducing mnt_clone_write, which avoids some heavyweight operations of mnt_want_write if called on a vfsmount which we know already has a write count; and mnt_want_write_file, which can call mnt_clone_write if the file is open for write. After these two patches, mnt_want_write and mnt_drop_write go from 7% on the profile down to 1.3% (including mnt_clone_write). [AV: mnt_want_write_file() should take file alone and derive mnt from it; not only all callers have that form, but that's the only mnt about which we know that it's already held for write if file is opened for write] Cc: Dave Hansen Signed-off-by: Nick Piggin Signed-off-by: Al Viro --- fs/namespace.c | 40 ++++++++++++++++++++++++++++++++++++++++ 1 file changed, 40 insertions(+) (limited to 'fs/namespace.c') diff --git a/fs/namespace.c b/fs/namespace.c index 22ae06ad751..120b8a6b99e 100644 --- a/fs/namespace.c +++ b/fs/namespace.c @@ -264,6 +264,46 @@ out: } EXPORT_SYMBOL_GPL(mnt_want_write); +/** + * mnt_clone_write - get write access to a mount + * @mnt: the mount on which to take a write + * + * This is effectively like mnt_want_write, except + * it must only be used to take an extra write reference + * on a mountpoint that we already know has a write reference + * on it. This allows some optimisation. + * + * After finished, mnt_drop_write must be called as usual to + * drop the reference. + */ +int mnt_clone_write(struct vfsmount *mnt) +{ + /* superblock may be r/o */ + if (__mnt_is_readonly(mnt)) + return -EROFS; + preempt_disable(); + inc_mnt_writers(mnt); + preempt_enable(); + return 0; +} +EXPORT_SYMBOL_GPL(mnt_clone_write); + +/** + * mnt_want_write_file - get write access to a file's mount + * @file: the file who's mount on which to take a write + * + * This is like mnt_want_write, but it takes a file and can + * do some optimisations if the file is open for write already + */ +int mnt_want_write_file(struct file *file) +{ + if (!(file->f_mode & FMODE_WRITE)) + return mnt_want_write(file->f_path.mnt); + else + return mnt_clone_write(file->f_path.mnt); +} +EXPORT_SYMBOL_GPL(mnt_want_write_file); + /** * mnt_drop_write - give up write access to a mount * @mnt: the mount on which to give up write access -- cgit v1.2.3