Re: [PATCH 5/8] xfs: factor out log write ordering from xlog_cil_push_work()

Darrick J. Wong
2021-06-17T19:59:06Z

On Thu, Jun 17, 2021 at 06:26:14PM +1000, Dave Chinner wrote:
> From: Dave Chinner <dchinner@redhat.com>
>
> So we can use it for start record ordering as well as commit record
> ordering in future.
>
> Signed-off-by: Dave Chinner <dchinner@redhat.com>

This tricked me for a second until I realized that xlog_cil_order_write
is the chunk of code just prior to the xlog_cil_write_commit_record
call.

Reviewed-by: Darrick J. Wong <djwong@kernel.org>

--D

> ---
> fs/xfs/xfs_log_cil.c | 89 ++++++++++++++++++++++++++------------------
> 1 file changed, 52 insertions(+), 37 deletions(-)
>
> diff --git a/fs/xfs/xfs_log_cil.c b/fs/xfs/xfs_log_cil.c
> index 35fc3e57d870..f993ec69fc97 100644
> --- a/fs/xfs/xfs_log_cil.c
> +++ b/fs/xfs/xfs_log_cil.c
> @@ -784,9 +784,54 @@ xlog_cil_build_trans_hdr(
> }
>
> /*
> - * Write out the commit record of a checkpoint transaction associated with the
> - * given ticket to close off a running log write. Return the lsn of the commit
> - * record.
> + * Ensure that the order of log writes follows checkpoint sequence order. This
> + * relies on the context LSN being zero until the log write has guaranteed the
> + * LSN that the log write will start at via xlog_state_get_iclog_space().
> + */
> +static int
> +xlog_cil_order_write(
> + struct xfs_cil *cil,
> + xfs_csn_t sequence)
> +{
> + struct xfs_cil_ctx *ctx;
> +
> +restart:
> + spin_lock(&cil->xc_push_lock);
> + list_for_each_entry(ctx, &cil->xc_committing, committing) {
> + /*
> + * Avoid getting stuck in this loop because we were woken by the
> + * shutdown, but then went back to sleep once already in the
> + * shutdown state.
> + */
> + if (XLOG_FORCED_SHUTDOWN(cil->xc_log)) {
> + spin_unlock(&cil->xc_push_lock);
> + return -EIO;
> + }
> +
> + /*
> + * Higher sequences will wait for this one so skip them.
> + * Don't wait for our own sequence, either.
> + */
> + if (ctx->sequence >= sequence)
> + continue;
> + if (!ctx->commit_lsn) {
> + /*
> + * It is still being pushed! Wait for the push to
> + * complete, then start again from the beginning.
> + */
> + xlog_wait(&cil->xc_commit_wait, &cil->xc_push_lock);
> + goto restart;
> + }
> + }
> + spin_unlock(&cil->xc_push_lock);
> + return 0;
> +}
> +
> +/*
> + * Write out the commit record of a checkpoint transaction to close off a
> + * running log write. These commit records are strictly ordered in ascending CIL
> + * sequence order so that log recovery will always replay the checkpoints in the
> + * correct order.
> */
> int
> xlog_cil_write_commit_record(
> @@ -816,6 +861,10 @@ xlog_cil_write_commit_record(
> if (XLOG_FORCED_SHUTDOWN(log))
> return -EIO;
>
> + error = xlog_cil_order_write(ctx->cil, ctx->sequence);
> + if (error)
> + return error;
> +
> /* account for space used by record data */
> ctx->ticket->t_curr_res -= reg.i_len;
> error = xlog_write(log, ctx, &lv_chain, ctx->ticket, iclog, reg.i_len);
> @@ -1048,40 +1097,6 @@ xlog_cil_push_work(
> if (error)
> goto out_abort_free_ticket;
>
> - /*
> - * now that we've written the checkpoint into the log, strictly
> - * order the commit records so replay will get them in the right order.
> - */
> -restart:
> - spin_lock(&cil->xc_push_lock);
> - list_for_each_entry(new_ctx, &cil->xc_committing, committing) {
> - /*
> - * Avoid getting stuck in this loop because we were woken by the
> - * shutdown, but then went back to sleep once already in the
> - * shutdown state.
> - */
> - if (XLOG_FORCED_SHUTDOWN(log)) {
> - spin_unlock(&cil->xc_push_lock);
> - goto out_abort_free_ticket;
> - }
> -
> - /*
> - * Higher sequences will wait for this one so skip them.
> - * Don't wait for our own sequence, either.
> - */
> - if (new_ctx->sequence >= ctx->sequence)
> - continue;
> - if (!new_ctx->commit_lsn) {
> - /*
> - * It is still being pushed! Wait for the push to
> - * complete, then start again from the beginning.
> - */
> - xlog_wait(&cil->xc_commit_wait, &cil->xc_push_lock);
> - goto restart;
> - }
> - }
> - spin_unlock(&cil->xc_push_lock);
> -
> error = xlog_cil_write_commit_record(ctx, &commit_iclog);
> if (error)
> goto out_abort_free_ticket;
> --
> 2.31.1
>