On Tue, Mar 24, 2020 at 06:44:52PM +0100, Christoph Hellwig wrote:
> From: Dave Chinner <dchinner@xxxxxxxxxx>
>
> The xlog_write() function iterates over iclogs until it completes
> writing all the log vectors passed in. The ticket tracks whether
> a start record has been written or not, so only the first iclog gets
> a start record. We only ever pass single use tickets to
> xlog_write() so we only ever need to write a start record once per
> xlog_write() call.
>
> Hence we don't need to store whether we should write a start record
> in the ticket as the callers provide all the information we need to
> determine if a start record should be written. For the moment, we
> have to ensure that we clear the XLOG_TIC_INITED appropriately so
> the code in xfs_log_done() still works correctly for committing
> transactions.
>
> Signed-off-by: Dave Chinner <dchinner@xxxxxxxxxx>
> [hch: use an need_start_rec bool]
> Signed-off-by: Christoph Hellwig <hch@xxxxxx>
> ---
> fs/xfs/xfs_log.c | 63 ++++++++++++++++++++++++------------------------
> 1 file changed, 32 insertions(+), 31 deletions(-)
>
> diff --git a/fs/xfs/xfs_log.c b/fs/xfs/xfs_log.c
> index 2a90a483c2d6..bf071552094a 100644
> --- a/fs/xfs/xfs_log.c
> +++ b/fs/xfs/xfs_log.c
...
> @@ -2372,25 +2359,29 @@ xlog_write(
> int record_cnt = 0;
> int data_cnt = 0;
> int error = 0;
> + bool need_start_rec = true;
>
> *start_lsn = 0;
>
> - len = xlog_write_calc_vec_length(ticket, log_vector);
>
> /*
> * Region headers and bytes are already accounted for.
> * We only need to take into account start records and
> * split regions in this function.
> */
> - if (ticket->t_flags & XLOG_TIC_INITED)
> - ticket->t_curr_res -= sizeof(xlog_op_header_t);
> + if (ticket->t_flags & XLOG_TIC_INITED) {
> + ticket->t_curr_res -= sizeof(struct xlog_op_header);
> + ticket->t_flags &= ~XLOG_TIC_INITED;
> + }
>
> /*
> * Commit record headers need to be accounted for. These
> * come in as separate writes so are easy to detect.
> */
> - if (flags & (XLOG_COMMIT_TRANS | XLOG_UNMOUNT_TRANS))
> - ticket->t_curr_res -= sizeof(xlog_op_header_t);
> + if (flags & (XLOG_COMMIT_TRANS | XLOG_UNMOUNT_TRANS)) {
> + ticket->t_curr_res -= sizeof(struct xlog_op_header);
> + need_start_rec = false;
> + }
Hmm.. I was asking for a comment update in v1 for this logic change.
Looking through it again, what happens here if
xfs_log_write_unmount_record() clears the UNMOUNT_TRANS flag for that
summary counter check? That looks like a potential behavior change wrt
to the start record..
Brian
>
> if (ticket->t_curr_res < 0) {
> xfs_alert_tag(log->l_mp, XFS_PTAG_LOGRES,
> @@ -2399,6 +2390,8 @@ xlog_write(
> xfs_force_shutdown(log->l_mp, SHUTDOWN_LOG_IO_ERROR);
> }
>
> + len = xlog_write_calc_vec_length(ticket, log_vector, need_start_rec);
> +
> index = 0;
> lv = log_vector;
> vecp = lv->lv_iovecp;
> @@ -2425,7 +2418,6 @@ xlog_write(
> while (lv && (!lv->lv_niovecs || index < lv->lv_niovecs)) {
> struct xfs_log_iovec *reg;
> struct xlog_op_header *ophdr;
> - int start_rec_copy;
> int copy_len;
> int copy_off;
> bool ordered = false;
> @@ -2441,11 +2433,15 @@ xlog_write(
> ASSERT(reg->i_len % sizeof(int32_t) == 0);
> ASSERT((unsigned long)ptr % sizeof(int32_t) == 0);
>
> - start_rec_copy = xlog_write_start_rec(ptr, ticket);
> - if (start_rec_copy) {
> - record_cnt++;
> + /*
> + * Before we start formatting log vectors, we need to
> + * write a start record. Only do this for the first
> + * iclog we write to.
> + */
> + if (need_start_rec) {
> + xlog_write_start_rec(ptr, ticket);
> xlog_write_adv_cnt(&ptr, &len, &log_offset,
> - start_rec_copy);
> + sizeof(struct xlog_op_header));
> }
>
> ophdr = xlog_write_setup_ophdr(log, ptr, ticket, flags);
> @@ -2477,8 +2473,13 @@ xlog_write(
> xlog_write_adv_cnt(&ptr, &len, &log_offset,
> copy_len);
> }
> - copy_len += start_rec_copy + sizeof(xlog_op_header_t);
> + copy_len += sizeof(struct xlog_op_header);
> record_cnt++;
> + if (need_start_rec) {
> + copy_len += sizeof(struct xlog_op_header);
> + record_cnt++;
> + need_start_rec = false;
> + }
> data_cnt += contwr ? copy_len : 0;
>
> error = xlog_write_copy_finish(log, iclog, flags,
> --
> 2.25.1
>
