• J
    jbd2: speedup jbd2_journal_get_[write|undo]_access() · de92c8ca
    Jan Kara 提交于
    jbd2_journal_get_write_access() and jbd2_journal_get_create_access() are
    frequently called for buffers that are already part of the running
    transaction - most frequently it is the case for bitmaps, inode table
    blocks, and superblock. Since in such cases we have nothing to do, it is
    unfortunate we still grab reference to journal head, lock the bh, lock
    bh_state only to find out there's nothing to do.
    
    Improving this is a bit subtle though since until we find out journal
    head is attached to the running transaction, it can disappear from under
    us because checkpointing / commit decided it's no longer needed. We deal
    with this by protecting journal_head slab with RCU. We still have to be
    careful about journal head being freed & reallocated within slab and
    about exposing journal head in consistent state (in particular
    b_modified and b_frozen_data must be in correct state before we allow
    user to touch the buffer).
    Signed-off-by: NJan Kara <jack@suse.cz>
    Signed-off-by: NTheodore Ts'o <tytso@mit.edu>
    de92c8ca
journal.c 73.8 KB