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    Subject[PATCH 4/8] jbd: use WRITE_SYNC_PLUG instead of WRITE_SYNC
    Date
    When you are going to be submitting several sync writes, we want to
    give the IO scheduler a chance to merge some of them. Instead of
    using the implicitly unplugging WRITE_SYNC variant, use WRITE_SYNC_PLUG
    and rely on sync_buffer() doing the unplug when someone does a
    wait_on_buffer()/lock_buffer().

    Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
    ---
    fs/jbd/commit.c | 7 ++++++-
    1 files changed, 6 insertions(+), 1 deletions(-)

    diff --git a/fs/jbd/commit.c b/fs/jbd/commit.c
    index f8077b9..a8e8513 100644
    --- a/fs/jbd/commit.c
    +++ b/fs/jbd/commit.c
    @@ -351,8 +351,13 @@ void journal_commit_transaction(journal_t *journal)
    spin_lock(&journal->j_state_lock);
    commit_transaction->t_state = T_LOCKED;

    + /*
    + * Use plugged writes here, since we want to submit several before
    + * we unplug the device. We don't do explicit unplugging in here,
    + * instead we rely on sync_buffer() doing the unplug for us.
    + */
    if (commit_transaction->t_synchronous_commit)
    - write_op = WRITE_SYNC;
    + write_op = WRITE_SYNC_PLUG;
    spin_lock(&commit_transaction->t_handle_lock);
    while (commit_transaction->t_updates) {
    DEFINE_WAIT(wait);
    --
    1.6.2.1.423.g442d


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