On Fri 31-07-15 17:11:34, Lukas Czerner wrote:
> Currently there is no limitation on number of reserved credits we can
> ask for. If we ask for more reserved credits than 1/2 of maximum
> transaction size, or if total number of credits exceeds the maximum
> transaction size per operation (which is currently only possible with
> the former) we will spin forever in start_this_handle().
>
> Fix this by adding this limitation at the start of start_this_handle().
>
> This patch also removes the credit limitation 1/2 of maximum transaction
> size, since we really only want to limit the number of reserved credits.
> There is not much point to limit the credits if there is still space in
> the journal.
>
> This accidentally also fixes the online resize, where due to the
> limitation of the journal credits we're unable to grow file systems with
> 1k block size and size between 16M and 32M. It has been partially fixed
> by 2c869b262a10ca99cb866d04087d75311587a30c, but not entirely.
>
> Thanks Jan Kara for helping me getting the correct fix.
>
> Signed-off-by: Lukas Czerner <lczerner@xxxxxxxxxx>
> ---
> v2: added wait event Jan suggested
The patch looks good. You can add:
Reviewed-by: Jan Kara <jack@xxxxxxx>
Honza
>
> fs/jbd2/transaction.c | 36 +++++++++++++++++++++++++++---------
> 1 file changed, 27 insertions(+), 9 deletions(-)
>
> diff --git a/fs/jbd2/transaction.c b/fs/jbd2/transaction.c
> index f3d0617..f8183d4 100644
> --- a/fs/jbd2/transaction.c
> +++ b/fs/jbd2/transaction.c
> @@ -204,6 +204,20 @@ static int add_transaction_credits(journal_t *journal, int blocks,
> * attach this handle to a new transaction.
> */
> atomic_sub(total, &t->t_outstanding_credits);
> +
> + /*
> + * Is the number of reserved credits in the current transaction too
> + * big to fit this handle? Wait until reserved credits are freed.
> + */
> + if (atomic_read(&journal->j_reserved_credits) + total >
> + journal->j_max_transaction_buffers) {
> + read_unlock(&journal->j_state_lock);
> + wait_event(journal->j_wait_reserved,
> + atomic_read(&journal->j_reserved_credits) + total <=
> + journal->j_max_transaction_buffers);
> + return 1;
> + }
> +
> wait_transaction_locked(journal);
> return 1;
> }
> @@ -262,20 +276,24 @@ static int start_this_handle(journal_t *journal, handle_t *handle,
> int rsv_blocks = 0;
> unsigned long ts = jiffies;
>
> + if (handle->h_rsv_handle)
> + rsv_blocks = handle->h_rsv_handle->h_buffer_credits;
> +
> /*
> - * 1/2 of transaction can be reserved so we can practically handle
> - * only 1/2 of maximum transaction size per operation
> + * Limit the number of reserved credits to 1/2 of maximum transaction
> + * size and limit the number of total credits to not exceed maximum
> + * transaction size per operation.
> */
> - if (WARN_ON(blocks > journal->j_max_transaction_buffers / 2)) {
> - printk(KERN_ERR "JBD2: %s wants too many credits (%d > %d)\n",
> - current->comm, blocks,
> - journal->j_max_transaction_buffers / 2);
> + if ((rsv_blocks > journal->j_max_transaction_buffers / 2) ||
> + (rsv_blocks + blocks > journal->j_max_transaction_buffers)) {
> + printk(KERN_ERR "JBD2: %s wants too many credits "
> + "credits:%d rsv_credits:%d max:%d\n",
> + current->comm, blocks, rsv_blocks,
> + journal->j_max_transaction_buffers);
> + WARN_ON(1);
> return -ENOSPC;
> }
>
> - if (handle->h_rsv_handle)
> - rsv_blocks = handle->h_rsv_handle->h_buffer_credits;
> -
> alloc_transaction:
> if (!journal->j_running_transaction) {
> /*
> --
> 1.8.3.1
>
--
Jan Kara <jack@xxxxxxxx>
SUSE Labs, CR
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