On May 18, 2020, at 3:21 AM, Jan Kara <jack@xxxxxxx> wrote:
>
> When reserved transaction handle is unused, we subtract its reserved
> credits in __jbd2_journal_unreserve_handle() called from
> jbd2_journal_stop(). However this function forgets to remove reserved
> credits from transaction->t_outstanding_credits and thus the transaction
> space that was reserved remains effectively leaked. The leaked
> transaction space can be quite significant in some cases and leads to
> unnecessarily small transactions and thus reducing throughput of the
> journalling machinery. E.g. fsmark workload creating lots of 4k files
> was observed to have about 20% lower throughput due to this when ext4 is
> mounted with dioread_nolock mount option.
>
> Subtract reserved credits from t_outstanding_credits as well.
>
> CC: stable@xxxxxxxxxxxxxxx
> Fixes: 8f7d89f36829 ("jbd2: transaction reservation support")
> Signed-off-by: Jan Kara <jack@xxxxxxx>
Patch looks reasonable, with one minor nit below.
Reviewed-by: Andreas Dilger <adilger@xxxxxxxxx>
> ---
> fs/jbd2/transaction.c | 17 +++++++++++++----
> 1 file changed, 13 insertions(+), 4 deletions(-)
>
> diff --git a/fs/jbd2/transaction.c b/fs/jbd2/transaction.c
> index 3dccc23cf010..b49a103cff1f 100644
> --- a/fs/jbd2/transaction.c
> +++ b/fs/jbd2/transaction.c
> @@ -541,17 +541,24 @@ handle_t *jbd2_journal_start(journal_t *journal, int nblocks)
> }
> EXPORT_SYMBOL(jbd2_journal_start);
>
> -static void __jbd2_journal_unreserve_handle(handle_t *handle)
> +static void __jbd2_journal_unreserve_handle(handle_t *handle, transaction_t *t)
> {
> journal_t *journal = handle->h_journal;
>
> WARN_ON(!handle->h_reserved);
> sub_reserved_credits(journal, handle->h_total_credits);
> + if (t)
> + atomic_sub(handle->h_total_credits, &t->t_outstanding_credits);
> }
>
> void jbd2_journal_free_reserved(handle_t *handle)
> {
> - __jbd2_journal_unreserve_handle(handle);
> + journal_t *journal = handle->h_journal;
> +
> + /* Get j_state_lock to pin running transaction if it exists */
> + read_lock(&journal->j_state_lock);
> + __jbd2_journal_unreserve_handle(handle, journal->j_running_transaction);
> + read_unlock(&journal->j_state_lock);
> jbd2_free_handle(handle);
> }
> EXPORT_SYMBOL(jbd2_journal_free_reserved);
> @@ -721,8 +728,10 @@ static void stop_this_handle(handle_t *handle)
> }
> atomic_sub(handle->h_total_credits,
> &transaction->t_outstanding_credits);
> - if (handle->h_rsv_handle)
> - __jbd2_journal_unreserve_handle(handle->h_rsv_handle);
> + if (handle->h_rsv_handle) {
> + __jbd2_journal_unreserve_handle(handle->h_rsv_handle,
> + transaction);
> + }
There isn't any need for braces {} around this one-line if-block.
Cheers, Andreas
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