• Chris Mason's avatar
    Btrfs: switch the btrfs tree locks to reader/writer · bd681513
    Chris Mason authored
    The btrfs metadata btree is the source of significant
    lock contention, especially in the root node.   This
    commit changes our locking to use a reader/writer
    lock.
    
    The lock is built on top of rw spinlocks, and it
    extends the lock tracking to remember if we have a
    read lock or a write lock when we go to blocking.  Atomics
    count the number of blocking readers or writers at any
    given time.
    
    It removes all of the adaptive spinning from the old code
    and uses only the spinning/blocking hints inside of btrfs
    to decide when it should continue spinning.
    
    In read heavy workloads this is dramatically faster.  In write
    heavy workloads we're still faster because of less contention
    on the root node lock.
    
    We suffer slightly in dbench because we schedule more often
    during write locks, but all other benchmarks so far are improved.
    Signed-off-by: default avatarChris Mason <chris.mason@oracle.com>
    bd681513
extent_io.h 11 KB