• npiggin@suse.de's avatar
    fs: introduce mnt_clone_write · 96029c4e
    npiggin@suse.de authored
    
    
    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 <haveblue@us.ibm.com>
    Signed-off-by: default avatarNick Piggin <npiggin@suse.de>
    Signed-off-by: default avatarAl Viro <viro@zeniv.linux.org.uk>
    96029c4e