• Jan Kara's avatar
    jbd2: fix dbench4 performance regression for 'nobarrier' mounts · 7621cb79
    Jan Kara authored
    commit 5052b069 upstream.
    
    Commit b685d3d6 "block: treat REQ_FUA and REQ_PREFLUSH as
    synchronous" removed REQ_SYNC flag from WRITE_FUA implementation. Since
    JBD2 strips REQ_FUA and REQ_FLUSH flags from submitted IO when the
    filesystem is mounted with nobarrier mount option, journal superblock
    writes ended up being async writes after this patch and that caused
    heavy performance regression for dbench4 benchmark with high number of
    processes. In my test setup with HP RAID array with non-volatile write
    cache and 32 GB ram, dbench4 runs with 8 processes regressed by ~25%.
    
    Fix the problem by making sure journal superblock writes are always
    treated as synchronous since they generally block progress of the
    journalling machinery and thus the whole filesystem.
    
    Fixes: b685d3d6Signed-off-by: default avatarJan Kara <jack@suse.cz>
    Signed-off-by: default avatarTheodore Ts'o <tytso@mit.edu>
    Signed-off-by: default avatarGreg Kroah-Hartman <gregkh@linuxfoundation.org>
    7621cb79
journal.c 74.3 KB