• Christoph Hellwig's avatar
    fs: kill i_alloc_sem · bd5fe6c5
    Christoph Hellwig authored
    
    
    i_alloc_sem is a rather special rw_semaphore.  It's the last one that may
    be released by a non-owner, and it's write side is always mirrored by
    real exclusion.  It's intended use it to wait for all pending direct I/O
    requests to finish before starting a truncate.
    
    Replace it with a hand-grown construct:
    
     - exclusion for truncates is already guaranteed by i_mutex, so it can
       simply fall way
     - the reader side is replaced by an i_dio_count member in struct inode
       that counts the number of pending direct I/O requests.  Truncate can't
       proceed as long as it's non-zero
     - when i_dio_count reaches non-zero we wake up a pending truncate using
       wake_up_bit on a new bit in i_flags
     - new references to i_dio_count can't appear while we are waiting for
       it to read zero because the direct I/O count always needs i_mutex
       (or an equivalent like XFS's i_iolock) for starting a new operation.
    
    This scheme is much simpler, and saves the space of a spinlock_t and a
    struct list_head in struct inode (typically 160 bits on a non-debug 64-bit
    system).
    Signed-off-by: default avatarChristoph Hellwig <hch@lst.de>
    Signed-off-by: default avatarAl Viro <viro@zeniv.linux.org.uk>
    bd5fe6c5
filemap.c 69.2 KB