Re: [PATCH 6/8] xfs: factor iclog state processing out of xlog_state_do_callback()

Darrick J. Wong
2019-09-05T15:47:11Z

On Thu, Sep 05, 2019 at 06:47:15PM +1000, Dave Chinner wrote:
> From: Dave Chinner <dchinner@redhat.com>
>
> The iclog IO completion state processing is somewhat complex, and
> because it's inside two nested loops it is highly indented and very
> hard to read. Factor it out, flatten the logic flow and clean up the
> comments so that it much easier to see what the code is doing both
> in processing the individual iclogs and in the over
> xlog_state_do_callback() operation.
>
> Signed-off-by: Dave Chinner <dchinner@redhat.com>

Looks ok,
Reviewed-by: Darrick J. Wong <darrick.wong@oracle.com>

--D

> ---
> fs/xfs/xfs_log.c | 195 ++++++++++++++++++++++++-----------------------
> 1 file changed, 98 insertions(+), 97 deletions(-)
>
> diff --git a/fs/xfs/xfs_log.c b/fs/xfs/xfs_log.c
> index 73aa8e152c83..356204ddf865 100644
> --- a/fs/xfs/xfs_log.c
> +++ b/fs/xfs/xfs_log.c
> @@ -2628,6 +2628,90 @@ xlog_get_lowest_lsn(
> return lowest_lsn;
> }
>
> +/*
> + * Return true if we need to stop processing, false to continue to the next
> + * iclog. The caller will need to run callbacks if the iclog is returned in the
> + * XLOG_STATE_CALLBACK state.
> + */
> +static bool
> +xlog_state_iodone_process_iclog(
> + struct xlog *log,
> + struct xlog_in_core *iclog,
> + struct xlog_in_core *completed_iclog,
> + bool *ioerror)
> +{
> + xfs_lsn_t lowest_lsn;
> +
> + /* Skip all iclogs in the ACTIVE & DIRTY states */
> + if (iclog->ic_state & (XLOG_STATE_ACTIVE | XLOG_STATE_DIRTY))
> + return false;
> +
> + /*
> + * Between marking a filesystem SHUTDOWN and stopping the log, we do
> + * flush all iclogs to disk (if there wasn't a log I/O error). So, we do
> + * want things to go smoothly in case of just a SHUTDOWN w/o a
> + * LOG_IO_ERROR.
> + */
> + if (iclog->ic_state & XLOG_STATE_IOERROR) {
> + *ioerror = true;
> + return false;
> + }
> +
> + /*
> + * Can only perform callbacks in order. Since this iclog is not in the
> + * DONE_SYNC/ DO_CALLBACK state, we skip the rest and just try to clean
> + * up. If we set our iclog to DO_CALLBACK, we will not process it when
> + * we retry since a previous iclog is in the CALLBACK and the state
> + * cannot change since we are holding the l_icloglock.
> + */
> + if (!(iclog->ic_state &
> + (XLOG_STATE_DONE_SYNC | XLOG_STATE_DO_CALLBACK))) {
> + if (completed_iclog &&
> + (completed_iclog->ic_state == XLOG_STATE_DONE_SYNC)) {
> + completed_iclog->ic_state = XLOG_STATE_DO_CALLBACK;
> + }
> + return true;
> + }
> +
> + /*
> + * We now have an iclog that is in either the DO_CALLBACK or DONE_SYNC
> + * states. The other states (WANT_SYNC, SYNCING, or CALLBACK were caught
> + * by the above if and are going to clean (i.e. we aren't doing their
> + * callbacks) see the above if.
> + *
> + * We will do one more check here to see if we have chased our tail
> + * around.
> + */
> + lowest_lsn = xlog_get_lowest_lsn(log);
> + if (lowest_lsn &&
> + XFS_LSN_CMP(lowest_lsn, be64_to_cpu(iclog->ic_header.h_lsn)) < 0)
> + return false; /* Leave this iclog for another thread */
> +
> + iclog->ic_state = XLOG_STATE_CALLBACK;
> +
> + /*
> + * Completion of a iclog IO does not imply that a transaction has
> + * completed, as transactions can be large enough to span many iclogs.
> + * We cannot change the tail of the log half way through a transaction
> + * as this may be the only transaction in the log and moving th etail to
> + * point to the middle of it will prevent recovery from finding the
> + * start of the transaction. Hence we should only update the
> + * last_sync_lsn if this iclog contains transaction completion callbacks
> + * on it.
> + *
> + * We have to do this before we drop the icloglock to ensure we are the
> + * only one that can update it.
> + */
> + ASSERT(XFS_LSN_CMP(atomic64_read(&log->l_last_sync_lsn),
> + be64_to_cpu(iclog->ic_header.h_lsn)) <= 0);
> + if (!list_empty_careful(&iclog->ic_callbacks))
> + atomic64_set(&log->l_last_sync_lsn,
> + be64_to_cpu(iclog->ic_header.h_lsn));
> +
> + return false;
> +
> +}
> +
> /*
> * Keep processing entries in the iclog callback list until we come around and
> * it is empty. We need to atomically see that the list is empty and change the
> @@ -2712,22 +2796,15 @@ xlog_state_do_callback(
> bool aborted,
> struct xlog_in_core *ciclog)
> {
> - xlog_in_core_t *iclog;
> - xlog_in_core_t *first_iclog; /* used to know when we've
> - * processed all iclogs once */
> - int flushcnt = 0;
> - xfs_lsn_t lowest_lsn;
> - int ioerrors; /* counter: iclogs with errors */
> - bool cycled_icloglock;
> - int funcdidcallbacks; /* flag: function did callbacks */
> - int repeats; /* for issuing console warnings if
> - * looping too many times */
> + struct xlog_in_core *iclog;
> + struct xlog_in_core *first_iclog;
> + int flushcnt = 0;
> + int funcdidcallbacks = 0;
> + bool cycled_icloglock;
> + bool ioerror;
> + int repeats = 0;
>
> spin_lock(&log->l_icloglock);
> - first_iclog = iclog = log->l_iclog;
> - ioerrors = 0;
> - funcdidcallbacks = 0;
> - repeats = 0;
>
> do {
> /*
> @@ -2741,96 +2818,20 @@ xlog_state_do_callback(
> first_iclog = log->l_iclog;
> iclog = log->l_iclog;
> cycled_icloglock = false;
> + ioerror = false;
> repeats++;
>
> do {
> + if (xlog_state_iodone_process_iclog(log, iclog,
> + ciclog, &ioerror))
> + break;
>
> - /* skip all iclogs in the ACTIVE & DIRTY states */
> - if (iclog->ic_state &
> - (XLOG_STATE_ACTIVE|XLOG_STATE_DIRTY)) {
> + if (!(iclog->ic_state &
> + (XLOG_STATE_CALLBACK | XLOG_STATE_IOERROR))) {
> iclog = iclog->ic_next;
> continue;
> }
>
> - /*
> - * Between marking a filesystem SHUTDOWN and stopping
> - * the log, we do flush all iclogs to disk (if there
> - * wasn't a log I/O error). So, we do want things to
> - * go smoothly in case of just a SHUTDOWN w/o a
> - * LOG_IO_ERROR.
> - */
> - if (!(iclog->ic_state & XLOG_STATE_IOERROR)) {
> - /*
> - * Can only perform callbacks in order. Since
> - * this iclog is not in the DONE_SYNC/
> - * DO_CALLBACK state, we skip the rest and
> - * just try to clean up. If we set our iclog
> - * to DO_CALLBACK, we will not process it when
> - * we retry since a previous iclog is in the
> - * CALLBACK and the state cannot change since
> - * we are holding the l_icloglock.
> - */
> - if (!(iclog->ic_state &
> - (XLOG_STATE_DONE_SYNC |
> - XLOG_STATE_DO_CALLBACK))) {
> - if (ciclog && (ciclog->ic_state ==
> - XLOG_STATE_DONE_SYNC)) {
> - ciclog->ic_state = XLOG_STATE_DO_CALLBACK;
> - }
> - break;
> - }
> - /*
> - * We now have an iclog that is in either the
> - * DO_CALLBACK or DONE_SYNC states. The other
> - * states (WANT_SYNC, SYNCING, or CALLBACK were
> - * caught by the above if and are going to
> - * clean (i.e. we aren't doing their callbacks)
> - * see the above if.
> - */
> -
> - /*
> - * We will do one more check here to see if we
> - * have chased our tail around.
> - */
> -
> - lowest_lsn = xlog_get_lowest_lsn(log);
> - if (lowest_lsn &&
> - XFS_LSN_CMP(lowest_lsn,
> - be64_to_cpu(iclog->ic_header.h_lsn)) < 0) {
> - iclog = iclog->ic_next;
> - continue; /* Leave this iclog for
> - * another thread */
> - }
> -
> - iclog->ic_state = XLOG_STATE_CALLBACK;
> -
> -
> - /*
> - * Completion of a iclog IO does not imply that
> - * a transaction has completed, as transactions
> - * can be large enough to span many iclogs. We
> - * cannot change the tail of the log half way
> - * through a transaction as this may be the only
> - * transaction in the log and moving th etail to
> - * point to the middle of it will prevent
> - * recovery from finding the start of the
> - * transaction. Hence we should only update the
> - * last_sync_lsn if this iclog contains
> - * transaction completion callbacks on it.
> - *
> - * We have to do this before we drop the
> - * icloglock to ensure we are the only one that
> - * can update it.
> - */
> - ASSERT(XFS_LSN_CMP(atomic64_read(&log->l_last_sync_lsn),
> - be64_to_cpu(iclog->ic_header.h_lsn)) <= 0);
> - if (!list_empty_careful(&iclog->ic_callbacks))
> - atomic64_set(&log->l_last_sync_lsn,
> - be64_to_cpu(iclog->ic_header.h_lsn));
> -
> - } else
> - ioerrors++;
> -
> /*
> * Running callbacks will drop the icloglock which means
> * we'll have to run at least one more complete loop.
> @@ -2862,7 +2863,7 @@ xlog_state_do_callback(
> "%s: possible infinite loop (%d iterations)",
> __func__, flushcnt);
> }
> - } while (!ioerrors && cycled_icloglock);
> + } while (!ioerror && cycled_icloglock);
>
> if (funcdidcallbacks)
> xlog_state_callback_check_state(log);
> --
> 2.23.0.rc1
>