Re: [PATCH 4/8] xfs: pass a CIL context to xlog_write()

Darrick J. Wong
2021-06-17T20:24:04Z

On Thu, Jun 17, 2021 at 06:26:13PM +1000, Dave Chinner wrote:
> From: Dave Chinner <dchinner@redhat.com>
>
> Pass the CIL context to xlog_write() rather than a pointer to a LSN
> variable. Only the CIL checkpoint calls to xlog_write() need to know
> about the start LSN of the writes, so rework xlog_write to directly
> write the LSNs into the CIL context structure.
>
> This removes the commit_lsn variable from xlog_cil_push_work(), so
> now we only have to issue the commit record ordering wakeup from
> there.
>
> Signed-off-by: Dave Chinner <dchinner@redhat.com>
> ---
> fs/xfs/xfs_log.c | 22 +++++++++++++++++-----
> fs/xfs/xfs_log_cil.c | 19 ++++++++-----------
> fs/xfs/xfs_log_priv.h | 4 ++--
> 3 files changed, 27 insertions(+), 18 deletions(-)
>
> diff --git a/fs/xfs/xfs_log.c b/fs/xfs/xfs_log.c
> index cf661c155786..fc0e43c57683 100644
> --- a/fs/xfs/xfs_log.c
> +++ b/fs/xfs/xfs_log.c
> @@ -871,7 +871,7 @@ xlog_write_unmount_record(
> */
> if (log->l_targ != log->l_mp->m_ddev_targp)
> blkdev_issue_flush(log->l_targ->bt_bdev);
> - return xlog_write(log, &lv_chain, ticket, NULL, NULL, reg.i_len);
> + return xlog_write(log, NULL, &lv_chain, ticket, NULL, reg.i_len);
> }
>
> /*
> @@ -2383,9 +2383,9 @@ xlog_write_partial(
> int
> xlog_write(
> struct xlog *log,
> + struct xfs_cil_ctx *ctx,
> struct list_head *lv_chain,
> struct xlog_ticket *ticket,
> - xfs_lsn_t *start_lsn,
> struct xlog_in_core **commit_iclog,
> uint32_t len)
> {
> @@ -2408,9 +2408,21 @@ xlog_write(
> if (error)
> return error;
>
> - /* start_lsn is the LSN of the first iclog written to. */
> - if (start_lsn)
> - *start_lsn = be64_to_cpu(iclog->ic_header.h_lsn);
> + /*
> + * If we have a CIL context, record the LSN of the iclog we were just
> + * granted space to start writing into. If the context doesn't have
> + * a start_lsn recorded, then this iclog will contain the start record
> + * for the checkpoint. Otherwise this write contains the commit record
> + * for the checkpoint.
> + */
> + if (ctx) {
> + spin_lock(&ctx->cil->xc_push_lock);
> + if (!ctx->start_lsn)
> + ctx->start_lsn = be64_to_cpu(iclog->ic_header.h_lsn);
> + else
> + ctx->commit_lsn = be64_to_cpu(iclog->ic_header.h_lsn);
> + spin_unlock(&ctx->cil->xc_push_lock);

This cycling of the push lock when setting start_lsn is new. What are
we protecting against here by taking the lock?

Also, just to check my assumptions: why do we take the push lock when
setting commit_lsn? Is that to synchronize with the xc_committing loop
that looks for contexts that need pushing?

--D

> + }
>
> lv = list_first_entry_or_null(lv_chain, struct xfs_log_vec, lv_list);
> while (lv) {
> diff --git a/fs/xfs/xfs_log_cil.c b/fs/xfs/xfs_log_cil.c
> index 2c8b25888c53..35fc3e57d870 100644
> --- a/fs/xfs/xfs_log_cil.c
> +++ b/fs/xfs/xfs_log_cil.c
> @@ -790,14 +790,13 @@ xlog_cil_build_trans_hdr(
> */
> int
> xlog_cil_write_commit_record(
> - struct xlog *log,
> - struct xlog_ticket *ticket,
> - struct xlog_in_core **iclog,
> - xfs_lsn_t *lsn)
> + struct xfs_cil_ctx *ctx,
> + struct xlog_in_core **iclog)
> {
> + struct xlog *log = ctx->cil->xc_log;
> struct xlog_op_header ophdr = {
> .oh_clientid = XFS_TRANSACTION,
> - .oh_tid = cpu_to_be32(ticket->t_tid),
> + .oh_tid = cpu_to_be32(ctx->ticket->t_tid),
> .oh_flags = XLOG_COMMIT_TRANS,
> };
> struct xfs_log_iovec reg = {
> @@ -818,8 +817,8 @@ xlog_cil_write_commit_record(
> return -EIO;
>
> /* account for space used by record data */
> - ticket->t_curr_res -= reg.i_len;
> - error = xlog_write(log, &lv_chain, ticket, lsn, iclog, reg.i_len);
> + ctx->ticket->t_curr_res -= reg.i_len;
> + error = xlog_write(log, ctx, &lv_chain, ctx->ticket, iclog, reg.i_len);
> if (error)
> xfs_force_shutdown(log->l_mp, SHUTDOWN_LOG_IO_ERROR);
> return error;
> @@ -1038,7 +1037,7 @@ xlog_cil_push_work(
> * use the commit record lsn then we can move the tail beyond the grant
> * write head.
> */
> - error = xlog_write(log, &ctx->lv_chain, ctx->ticket, &ctx->start_lsn,
> + error = xlog_write(log, ctx, &ctx->lv_chain, ctx->ticket,
> NULL, num_bytes);
>
> /*
> @@ -1083,8 +1082,7 @@ xlog_cil_push_work(
> }
> spin_unlock(&cil->xc_push_lock);
>
> - error = xlog_cil_write_commit_record(log, ctx->ticket, &commit_iclog,
> - &commit_lsn);
> + error = xlog_cil_write_commit_record(ctx, &commit_iclog);
> if (error)
> goto out_abort_free_ticket;
>
> @@ -1104,7 +1102,6 @@ xlog_cil_push_work(
> * and wake up anyone who is waiting for the commit to complete.
> */
> spin_lock(&cil->xc_push_lock);
> - ctx->commit_lsn = commit_lsn;
> wake_up_all(&cil->xc_commit_wait);
> spin_unlock(&cil->xc_push_lock);
>
> diff --git a/fs/xfs/xfs_log_priv.h b/fs/xfs/xfs_log_priv.h
> index 26f26769d1c6..af8a9dfa8068 100644
> --- a/fs/xfs/xfs_log_priv.h
> +++ b/fs/xfs/xfs_log_priv.h
> @@ -487,8 +487,8 @@ xlog_write_adv_cnt(void **ptr, int *len, int *off, size_t bytes)
>
> void xlog_print_tic_res(struct xfs_mount *mp, struct xlog_ticket *ticket);
> void xlog_print_trans(struct xfs_trans *);
> -int xlog_write(struct xlog *log, struct list_head *lv_chain,
> - struct xlog_ticket *tic, xfs_lsn_t *start_lsn,
> +int xlog_write(struct xlog *log, struct xfs_cil_ctx *ctx,
> + struct list_head *lv_chain, struct xlog_ticket *tic,
> struct xlog_in_core **commit_iclog, uint32_t len);
>
> void xfs_log_ticket_ungrant(struct xlog *log, struct xlog_ticket *ticket);
> --
> 2.31.1
>