diff mbox series

[29/45] xfs:_introduce xlog_write_partial()

Message ID 20210305051143.182133-30-david@fromorbit.com (mailing list archive)
State New
Headers show
Series xfs: consolidated log and optimisation changes | expand

Commit Message

Dave Chinner March 5, 2021, 5:11 a.m. UTC
From: Dave Chinner <dchinner@redhat.com>

Handle writing of a logvec chain into an iclog that doesn't have
enough space to fit it all. The iclog has already been changed to
WANT_SYNC by xlog_get_iclog_space(), so the entire remaining space
in the iclog is exclusively owned by this logvec chain.

The difference between the single and partial cases is that
we end up with partial iovec writes in the iclog and have to split
a log vec regions across two iclogs. The state handling for this is
currently awful and so we're building up the pieces needed to
handle this more cleanly one at a time.

Signed-off-by: Dave Chinner <dchinner@redhat.com>
---
 fs/xfs/xfs_log.c | 525 ++++++++++++++++++++++-------------------------
 1 file changed, 251 insertions(+), 274 deletions(-)

Comments

Darrick J. Wong March 9, 2021, 2:59 a.m. UTC | #1
On Fri, Mar 05, 2021 at 04:11:27PM +1100, Dave Chinner wrote:
> From: Dave Chinner <dchinner@redhat.com>
> 
> Handle writing of a logvec chain into an iclog that doesn't have
> enough space to fit it all. The iclog has already been changed to
> WANT_SYNC by xlog_get_iclog_space(), so the entire remaining space
> in the iclog is exclusively owned by this logvec chain.
> 
> The difference between the single and partial cases is that
> we end up with partial iovec writes in the iclog and have to split
> a log vec regions across two iclogs. The state handling for this is
> currently awful and so we're building up the pieces needed to
> handle this more cleanly one at a time.
> 
> Signed-off-by: Dave Chinner <dchinner@redhat.com>
> ---
>  fs/xfs/xfs_log.c | 525 ++++++++++++++++++++++-------------------------
>  1 file changed, 251 insertions(+), 274 deletions(-)
> 
> diff --git a/fs/xfs/xfs_log.c b/fs/xfs/xfs_log.c
> index 590c1e6db475..10916b99bf0f 100644
> --- a/fs/xfs/xfs_log.c
> +++ b/fs/xfs/xfs_log.c
> @@ -2099,166 +2099,250 @@ xlog_print_trans(
>  	}
>  }
>  
> -static xlog_op_header_t *
> -xlog_write_setup_ophdr(
> -	struct xlog_op_header	*ophdr,
> -	struct xlog_ticket	*ticket)
> -{
> -	ophdr->oh_clientid = XFS_TRANSACTION;
> -	ophdr->oh_res2 = 0;
> -	ophdr->oh_flags = 0;
> -	return ophdr;
> -}
> -
>  /*
> - * Set up the parameters of the region copy into the log. This has
> - * to handle region write split across multiple log buffers - this
> - * state is kept external to this function so that this code can
> - * be written in an obvious, self documenting manner.
> + * Write whole log vectors into a single iclog which is guaranteed to have
> + * either sufficient space for the entire log vector chain to be written or
> + * exclusive access to the remaining space in the iclog.
> + *
> + * Return the number of iovecs and data written into the iclog, as well as
> + * a pointer to the logvec that doesn't fit in the log (or NULL if we hit the
> + * end of the chain.
>   */
> -static int
> -xlog_write_setup_copy(
> +static struct xfs_log_vec *
> +xlog_write_single(

Ouch.  Could you fix the previous patch to move this new function a
little higher in the file (like above xlog_write_setup_ophdr) so that it
doesn't get shredded like this?

Sooo... I /think/ this looks all right, but this is a pretty long
reorganization.  I might revisit this in the morning. :/

(Skip to the second-to-last hunk, that's where the next comment is...)

> +	struct xfs_log_vec	*log_vector,
>  	struct xlog_ticket	*ticket,
> -	struct xlog_op_header	*ophdr,
> -	int			space_available,
> -	int			space_required,
> -	int			*copy_off,
> -	int			*copy_len,
> -	int			*last_was_partial_copy,
> -	int			*bytes_consumed)
> -{
> -	int			still_to_copy;
> -
> -	still_to_copy = space_required - *bytes_consumed;
> -	*copy_off = *bytes_consumed;
> -
> -	if (still_to_copy <= space_available) {
> -		/* write of region completes here */
> -		*copy_len = still_to_copy;
> -		ophdr->oh_len = cpu_to_be32(*copy_len);
> -		if (*last_was_partial_copy)
> -			ophdr->oh_flags |= (XLOG_END_TRANS|XLOG_WAS_CONT_TRANS);
> -		*last_was_partial_copy = 0;
> -		*bytes_consumed = 0;
> -		return 0;
> -	}
> -
> -	/* partial write of region, needs extra log op header reservation */
> -	*copy_len = space_available;
> -	ophdr->oh_len = cpu_to_be32(*copy_len);
> -	ophdr->oh_flags |= XLOG_CONTINUE_TRANS;
> -	if (*last_was_partial_copy)
> -		ophdr->oh_flags |= XLOG_WAS_CONT_TRANS;
> -	*bytes_consumed += *copy_len;
> -	(*last_was_partial_copy)++;
> -
> -	/* account for new log op header */
> -	ticket->t_curr_res -= sizeof(struct xlog_op_header);
> -
> -	return sizeof(struct xlog_op_header);
> -}
> -
> -static int
> -xlog_write_copy_finish(
> -	struct xlog		*log,
>  	struct xlog_in_core	*iclog,
> -	uint			flags,
> -	int			*record_cnt,
> -	int			*data_cnt,
> -	int			*partial_copy,
> -	int			*partial_copy_len,
> -	int			log_offset,
> -	struct xlog_in_core	**commit_iclog)
> +	uint32_t		*log_offset,
> +	uint32_t		*len,
> +	uint32_t		*record_cnt,
> +	uint32_t		*data_cnt)
>  {
> -	int			error;
> +	struct xfs_log_vec	*lv = log_vector;
> +	void			*ptr;
> +	int			index;
>  
> -	if (*partial_copy) {
> +	ASSERT(*log_offset + *len <= iclog->ic_size ||
> +		iclog->ic_state == XLOG_STATE_WANT_SYNC);
> +
> +	ptr = iclog->ic_datap + *log_offset;
> +	for (lv = log_vector; lv; lv = lv->lv_next) {
>  		/*
> -		 * This iclog has already been marked WANT_SYNC by
> -		 * xlog_state_get_iclog_space.
> +		 * If the entire log vec does not fit in the iclog, punt it to
> +		 * the partial copy loop which can handle this case.
>  		 */
> -		spin_lock(&log->l_icloglock);
> -		xlog_state_finish_copy(log, iclog, *record_cnt, *data_cnt);
> -		*record_cnt = 0;
> -		*data_cnt = 0;
> -		goto release_iclog;
> -	}
> +		if (lv->lv_niovecs &&
> +		    lv->lv_bytes > iclog->ic_size - *log_offset)
> +			break;
>  
> -	*partial_copy = 0;
> -	*partial_copy_len = 0;
> +		/*
> +		 * Ordered log vectors have no regions to write so this
> +		 * loop will naturally skip them.
> +		 */
> +		for (index = 0; index < lv->lv_niovecs; index++) {
> +			struct xfs_log_iovec	*reg = &lv->lv_iovecp[index];
> +			struct xlog_op_header	*ophdr = reg->i_addr;
>  
> -	if (iclog->ic_size - log_offset <= sizeof(xlog_op_header_t)) {
> -		/* no more space in this iclog - push it. */
> -		spin_lock(&log->l_icloglock);
> -		xlog_state_finish_copy(log, iclog, *record_cnt, *data_cnt);
> -		*record_cnt = 0;
> -		*data_cnt = 0;
> +			ASSERT(reg->i_len % sizeof(int32_t) == 0);
> +			ASSERT((unsigned long)ptr % sizeof(int32_t) == 0);
>  
> -		if (iclog->ic_state == XLOG_STATE_ACTIVE)
> -			xlog_state_switch_iclogs(log, iclog, 0);
> -		else
> -			ASSERT(iclog->ic_state == XLOG_STATE_WANT_SYNC ||
> -			       iclog->ic_state == XLOG_STATE_IOERROR);
> -		if (!commit_iclog)
> -			goto release_iclog;
> -		spin_unlock(&log->l_icloglock);
> -		ASSERT(flags & XLOG_COMMIT_TRANS);
> -		*commit_iclog = iclog;
> +			ophdr->oh_tid = cpu_to_be32(ticket->t_tid);
> +			ophdr->oh_len = cpu_to_be32(reg->i_len -
> +						sizeof(struct xlog_op_header));
> +			memcpy(ptr, reg->i_addr, reg->i_len);
> +			xlog_write_adv_cnt(&ptr, len, log_offset, reg->i_len);
> +			(*record_cnt)++;
> +			*data_cnt += reg->i_len;
> +		}
>  	}
> +	ASSERT(*len == 0 || lv);
> +	return lv;
> +}
>  
> -	return 0;
> +static int
> +xlog_write_get_more_iclog_space(
> +	struct xlog		*log,
> +	struct xlog_ticket	*ticket,
> +	struct xlog_in_core	**iclogp,
> +	uint32_t		*log_offset,
> +	uint32_t		len,
> +	uint32_t		*record_cnt,
> +	uint32_t		*data_cnt,
> +	int			*contwr)
> +{
> +	struct xlog_in_core	*iclog = *iclogp;
> +	int			error;
>  
> -release_iclog:
> +	spin_lock(&log->l_icloglock);
> +	xlog_state_finish_copy(log, iclog, *record_cnt, *data_cnt);
> +	ASSERT(iclog->ic_state == XLOG_STATE_WANT_SYNC ||
> +	       iclog->ic_state == XLOG_STATE_IOERROR);
>  	error = xlog_state_release_iclog(log, iclog);
>  	spin_unlock(&log->l_icloglock);
> -	return error;
> +	if (error)
> +		return error;
> +
> +	error = xlog_state_get_iclog_space(log, len, &iclog,
> +				ticket, contwr, log_offset);
> +	if (error)
> +		return error;
> +	*record_cnt = 0;
> +	*data_cnt = 0;
> +	*iclogp = iclog;
> +	return 0;
>  }
>  
>  /*
> - * Write log vectors into a single iclog which is guaranteed by the caller
> - * to have enough space to write the entire log vector into. Return the number
> - * of log vectors written into the iclog.
> + * Write log vectors into a single iclog which is smaller than the current chain
> + * length. We write until we cannot fit a full record into the remaining space
> + * and then stop. We return the log vector that is to be written that cannot
> + * wholly fit in the iclog.
>   */
> -static int
> -xlog_write_single(
> +static struct xfs_log_vec *
> +xlog_write_partial(
> +	struct xlog		*log,
>  	struct xfs_log_vec	*log_vector,
>  	struct xlog_ticket	*ticket,
> -	struct xlog_in_core	*iclog,
> -	uint32_t		log_offset,
> -	uint32_t		len)
> +	struct xlog_in_core	**iclogp,
> +	uint32_t		*log_offset,
> +	uint32_t		*len,
> +	uint32_t		*record_cnt,
> +	uint32_t		*data_cnt,
> +	int			*contwr)
>  {
> +	struct xlog_in_core	*iclog = *iclogp;
>  	struct xfs_log_vec	*lv = log_vector;
> +	struct xfs_log_iovec	*reg;
> +	struct xlog_op_header	*ophdr;
>  	void			*ptr;
>  	int			index = 0;
> -	int			record_cnt = 0;
> +	uint32_t		rlen;
> +	int			error;
>  
> -	ASSERT(log_offset + len <= iclog->ic_size);
> +	/* walk the logvec, copying until we run out of space in the iclog */
> +	ptr = iclog->ic_datap + *log_offset;
> +	for (index = 0; index < lv->lv_niovecs; index++) {
> +		uint32_t	reg_offset = 0;
> +
> +		reg = &lv->lv_iovecp[index];
> +		ASSERT(reg->i_len % sizeof(int32_t) == 0);
>  
> -	ptr = iclog->ic_datap + log_offset;
> -	for (lv = log_vector; lv; lv = lv->lv_next) {
>  		/*
> -		 * Ordered log vectors have no regions to write so this
> -		 * loop will naturally skip them.
> +		 * The first region of a continuation must have a non-zero
> +		 * length otherwise log recovery will just skip over it and
> +		 * start recovering from the next opheader it finds. Because we
> +		 * mark the next opheader as a continuation, recovery will then
> +		 * incorrectly add the continuation to the previous region and
> +		 * that breaks stuff.
> +		 *
> +		 * Hence if there isn't space for region data after the
> +		 * opheader, then we need to start afresh with a new iclog.
>  		 */
> -		for (index = 0; index < lv->lv_niovecs; index++) {
> -			struct xfs_log_iovec	*reg = &lv->lv_iovecp[index];
> -			struct xlog_op_header	*ophdr = reg->i_addr;
> +		if (iclog->ic_size - *log_offset <=
> +					sizeof(struct xlog_op_header)) {
> +			error = xlog_write_get_more_iclog_space(log, ticket,
> +					&iclog, log_offset, *len, record_cnt,
> +					data_cnt, contwr);
> +			if (error)
> +				return ERR_PTR(error);
> +			ptr = iclog->ic_datap + *log_offset;
> +		}
>  
> -			ASSERT(reg->i_len % sizeof(int32_t) == 0);
> -			ASSERT((unsigned long)ptr % sizeof(int32_t) == 0);
> +		ophdr = reg->i_addr;
> +		rlen = min_t(uint32_t, reg->i_len, iclog->ic_size - *log_offset);
> +
> +		ophdr->oh_tid = cpu_to_be32(ticket->t_tid);
> +		ophdr->oh_len = cpu_to_be32(rlen - sizeof(struct xlog_op_header));
> +		if (rlen != reg->i_len)
> +			ophdr->oh_flags |= XLOG_CONTINUE_TRANS;
>  
> +		ASSERT((unsigned long)ptr % sizeof(int32_t) == 0);
> +		xlog_verify_dest_ptr(log, ptr);
> +		memcpy(ptr, reg->i_addr, rlen);
> +		xlog_write_adv_cnt(&ptr, len, log_offset, rlen);
> +		(*record_cnt)++;
> +		*data_cnt += rlen;
> +
> +		if (rlen == reg->i_len)
> +			continue;
> +
> +		/*
> +		 * We now have a partially written iovec, but it can span
> +		 * multiple iclogs so we loop here. First we release the iclog
> +		 * we currently have, then we get a new iclog and add a new
> +		 * opheader. Then we continue copying from where we were until
> +		 * we either complete the iovec or fill the iclog. If we
> +		 * complete the iovec, then we increment the index and go right
> +		 * back to the top of the outer loop. if we fill the iclog, we
> +		 * run the inner loop again.
> +		 *
> +		 * This is complicated by the tail of a region using all the
> +		 * space in an iclog and hence requiring us to release the iclog
> +		 * and get a new one before returning to the outer loop. We must
> +		 * always guarantee that we exit this inner loop with at least
> +		 * space for log transaction opheaders left in the current
> +		 * iclog, hence we cannot just terminate the loop at the end
> +		 * of the of the continuation. So we loop while there is no
> +		 * space left in the current iclog, and check for the end of the
> +		 * continuation after getting a new iclog.
> +		 */
> +		do {
> +			/*
> +			 * Account for the continuation opheader before we get
> +			 * a new iclog. This is necessary so that we reserve
> +			 * space in the iclog for it.
> +			 */
> +			if (ophdr->oh_flags & XLOG_CONTINUE_TRANS) {
> +				*len += sizeof(struct xlog_op_header);
> +				ticket->t_curr_res -= sizeof(struct xlog_op_header);
> +			}
> +			error = xlog_write_get_more_iclog_space(log, ticket,
> +					&iclog, log_offset, *len, record_cnt,
> +					data_cnt, contwr);
> +			if (error)
> +				return ERR_PTR(error);
> +			ptr = iclog->ic_datap + *log_offset;
> +
> +			ophdr = ptr;
>  			ophdr->oh_tid = cpu_to_be32(ticket->t_tid);
> -			ophdr->oh_len = cpu_to_be32(reg->i_len -
> +			ophdr->oh_clientid = XFS_TRANSACTION;
> +			ophdr->oh_res2 = 0;
> +			ophdr->oh_flags = XLOG_WAS_CONT_TRANS;
> +
> +			xlog_write_adv_cnt(&ptr, len, log_offset,
>  						sizeof(struct xlog_op_header));
> -			memcpy(ptr, reg->i_addr, reg->i_len);
> -			xlog_write_adv_cnt(&ptr, &len, &log_offset, reg->i_len);
> -			record_cnt++;
> -		}
> +			*data_cnt += sizeof(struct xlog_op_header);
> +
> +			/*
> +			 * If rlen fits in the iclog, then end the region
> +			 * continuation. Otherwise we're going around again.
> +			 */
> +			reg_offset += rlen;
> +			rlen = reg->i_len - reg_offset;
> +			if (rlen <= iclog->ic_size - *log_offset)
> +				ophdr->oh_flags |= XLOG_END_TRANS;
> +			else
> +				ophdr->oh_flags |= XLOG_CONTINUE_TRANS;
> +
> +			rlen = min_t(uint32_t, rlen, iclog->ic_size - *log_offset);
> +			ophdr->oh_len = cpu_to_be32(rlen);
> +
> +			xlog_verify_dest_ptr(log, ptr);
> +			memcpy(ptr, reg->i_addr + reg_offset, rlen);
> +			xlog_write_adv_cnt(&ptr, len, log_offset, rlen);
> +			(*record_cnt)++;
> +			*data_cnt += rlen;
> +
> +		} while (ophdr->oh_flags & XLOG_CONTINUE_TRANS);
>  	}
> -	ASSERT(len == 0);
> -	return record_cnt;
> -}
>  
> +	/*
> +	 * No more iovecs remain in this logvec so return the next log vec to
> +	 * the caller so it can go back to fast path copying.
> +	 */
> +	*iclogp = iclog;
> +	return lv->lv_next;
> +}
>  
>  /*
>   * Write some region out to in-core log
> @@ -2312,14 +2396,11 @@ xlog_write(
>  {
>  	struct xlog_in_core	*iclog = NULL;
>  	struct xfs_log_vec	*lv = log_vector;
> -	struct xfs_log_iovec	*vecp = lv->lv_iovecp;
> -	int			index = 0;
> -	int			partial_copy = 0;
> -	int			partial_copy_len = 0;
>  	int			contwr = 0;
>  	int			record_cnt = 0;
>  	int			data_cnt = 0;
>  	int			error = 0;
> +	int			log_offset;
>  
>  	if (ticket->t_curr_res < 0) {
>  		xfs_alert_tag(log->l_mp, XFS_PTAG_LOGRES,
> @@ -2328,157 +2409,52 @@ xlog_write(
>  		xfs_force_shutdown(log->l_mp, SHUTDOWN_LOG_IO_ERROR);
>  	}
>  
> -	if (start_lsn)
> -		*start_lsn = 0;
> -	while (lv && (!lv->lv_niovecs || index < lv->lv_niovecs)) {
> -		void		*ptr;
> -		int		log_offset;
> -
> -		error = xlog_state_get_iclog_space(log, len, &iclog, ticket,
> -						   &contwr, &log_offset);
> -		if (error)
> -			return error;
> -
> -		ASSERT(log_offset <= iclog->ic_size - 1);
> +	error = xlog_state_get_iclog_space(log, len, &iclog, ticket,
> +					   &contwr, &log_offset);
> +	if (error)
> +		return error;
>  
> -		/* Start_lsn is the first lsn written to. */
> -		if (start_lsn && !*start_lsn)
> -			*start_lsn = be64_to_cpu(iclog->ic_header.h_lsn);
> +	/* start_lsn is the LSN of the first iclog written to. */
> +	if (start_lsn)
> +		*start_lsn = be64_to_cpu(iclog->ic_header.h_lsn);
>  
> -		/*
> -		 * iclogs containing commit records or unmount records need
> -		 * to issue ordering cache flushes and commit immediately
> -		 * to stable storage to guarantee journal vs metadata ordering
> -		 * is correctly maintained in the storage media.
> -		 */
> -		if (optype & (XLOG_COMMIT_TRANS | XLOG_UNMOUNT_TRANS)) {
> -			iclog->ic_flags |= (XLOG_ICL_NEED_FLUSH |
> -						XLOG_ICL_NEED_FUA);
> -		}
> +	/*
> +	 * iclogs containing commit records or unmount records need
> +	 * to issue ordering cache flushes and commit immediately
> +	 * to stable storage to guarantee journal vs metadata ordering
> +	 * is correctly maintained in the storage media. This will always
> +	 * fit in the iclog we have been already been passed.
> +	 */
> +	if (optype & (XLOG_COMMIT_TRANS | XLOG_UNMOUNT_TRANS)) {
> +		iclog->ic_flags |= (XLOG_ICL_NEED_FLUSH | XLOG_ICL_NEED_FUA);
> +		ASSERT(!contwr);
> +	}
>  
> -		/* If this is a single iclog write, go fast... */
> -		if (!contwr && lv == log_vector) {
> -			record_cnt = xlog_write_single(lv, ticket, iclog,
> -						log_offset, len);
> -			len = 0;
> -			data_cnt = len;
> +	while (lv) {
> +		lv = xlog_write_single(lv, ticket, iclog, &log_offset,
> +					&len, &record_cnt, &data_cnt);
> +		if (!lv)
>  			break;
> -		}
> -
> -		/*
> -		 * This loop writes out as many regions as can fit in the amount
> -		 * of space which was allocated by xlog_state_get_iclog_space().
> -		 */
> -		ptr = iclog->ic_datap + log_offset;
> -		while (lv && (!lv->lv_niovecs || index < lv->lv_niovecs)) {
> -			struct xfs_log_iovec	*reg;
> -			struct xlog_op_header	*ophdr;
> -			int			copy_len;
> -			int			copy_off;
> -			bool			ordered = false;
> -			bool			added_ophdr = false;
> -
> -			/* ordered log vectors have no regions to write */
> -			if (lv->lv_buf_len == XFS_LOG_VEC_ORDERED) {
> -				ASSERT(lv->lv_niovecs == 0);
> -				ordered = true;
> -				goto next_lv;
> -			}
> -
> -			reg = &vecp[index];
> -			ASSERT(reg->i_len % sizeof(int32_t) == 0);
> -			ASSERT((unsigned long)ptr % sizeof(int32_t) == 0);
> -
> -			/*
> -			 * Regions always have their ophdr at the start of the
> -			 * region, except for:
> -			 * - a transaction start which has a start record ophdr
> -			 *   before the first region ophdr; and
> -			 * - the previous region didn't fully fit into an iclog
> -			 *   so needs a continuation ophdr to prepend the region
> -			 *   in this new iclog.
> -			 */
> -			ophdr = reg->i_addr;
> -			if (optype && index) {
> -				optype &= ~XLOG_START_TRANS;
> -			} else if (partial_copy) {
> -                                ophdr = xlog_write_setup_ophdr(ptr, ticket);
> -				xlog_write_adv_cnt(&ptr, &len, &log_offset,
> -					   sizeof(struct xlog_op_header));
> -				added_ophdr = true;
> -			}
> -			ophdr->oh_tid = cpu_to_be32(ticket->t_tid);
> -
> -			len += xlog_write_setup_copy(ticket, ophdr,
> -						     iclog->ic_size-log_offset,
> -						     reg->i_len,
> -						     &copy_off, &copy_len,
> -						     &partial_copy,
> -						     &partial_copy_len);
> -			xlog_verify_dest_ptr(log, ptr);
> -
>  
> -			/*
> -			 * Wart: need to update length in embedded ophdr not
> -			 * to include it's own length.
> -			 */
> -			if (!added_ophdr) {
> -				ophdr->oh_len = cpu_to_be32(copy_len -
> -						sizeof(struct xlog_op_header));
> -			}
> -
> -			ASSERT(copy_len > 0);
> -			memcpy(ptr, reg->i_addr + copy_off, copy_len);
> -			xlog_write_adv_cnt(&ptr, &len, &log_offset, copy_len);
> -
> -			if (added_ophdr)
> -				copy_len += sizeof(struct xlog_op_header);
> -			record_cnt++;
> -			data_cnt += contwr ? copy_len : 0;
> -
> -			error = xlog_write_copy_finish(log, iclog, optype,
> -						       &record_cnt, &data_cnt,
> -						       &partial_copy,
> -						       &partial_copy_len,
> -						       log_offset,
> -						       commit_iclog);
> -			if (error)
> -				return error;
> -
> -			/*
> -			 * if we had a partial copy, we need to get more iclog
> -			 * space but we don't want to increment the region
> -			 * index because there is still more is this region to
> -			 * write.
> -			 *
> -			 * If we completed writing this region, and we flushed
> -			 * the iclog (indicated by resetting of the record
> -			 * count), then we also need to get more log space. If
> -			 * this was the last record, though, we are done and
> -			 * can just return.
> -			 */
> -			if (partial_copy)
> -				break;
> -
> -			if (++index == lv->lv_niovecs) {
> -next_lv:
> -				lv = lv->lv_next;
> -				index = 0;
> -				if (lv)
> -					vecp = lv->lv_iovecp;
> -			}
> -			if (record_cnt == 0 && !ordered) {
> -				if (!lv)
> -					return 0;
> -				break;
> -			}
> +		ASSERT(!(optype & (XLOG_COMMIT_TRANS | XLOG_UNMOUNT_TRANS)));
> +		lv = xlog_write_partial(log, lv, ticket, &iclog, &log_offset,
> +					&len, &record_cnt, &data_cnt, &contwr);
> +		if (IS_ERR_OR_NULL(lv)) {
> +			error = PTR_ERR_OR_ZERO(lv);
> +			break;
>  		}
>  	}
> +	ASSERT((len == 0 && !lv) || error);
>  
> -	ASSERT(len == 0);
> -
> +	/*
> +	 * We've already been guaranteed that the last writes will fit inside
> +	 * the current iclog, and hence it will already have the space used by
> +	 * those writes accounted to it. Hence we do not need to update the
> +	 * iclog with the number of bytes written here.
> +	 */
> +	ASSERT(!contwr || XLOG_FORCED_SHUTDOWN(log));
>  	spin_lock(&log->l_icloglock);
> -	xlog_state_finish_copy(log, iclog, record_cnt, data_cnt);
> +	xlog_state_finish_copy(log, iclog, record_cnt, 0);
>  	if (commit_iclog) {
>  		ASSERT(optype & XLOG_COMMIT_TRANS);
>  		*commit_iclog = iclog;
> @@ -2930,7 +2906,7 @@ xlog_state_get_iclog_space(
>  	 * xlog_write() algorithm assumes that at least 2 xlog_op_header_t's
>  	 * can fit into remaining data section.
>  	 */
> -	if (iclog->ic_size - iclog->ic_offset < 2*sizeof(xlog_op_header_t)) {
> +	if (iclog->ic_size - iclog->ic_offset < 3*sizeof(xlog_op_header_t)) {

Why does this change to 3?  Does the comment need amending?

--D

>  		int		error = 0;
>  
>  		xlog_state_switch_iclogs(log, iclog, iclog->ic_size);
> @@ -3633,11 +3609,12 @@ xlog_verify_iclog(
>  					iclog->ic_header.h_cycle_data[idx]);
>  			}
>  		}
> -		if (clientid != XFS_TRANSACTION && clientid != XFS_LOG)
> +		if (clientid != XFS_TRANSACTION && clientid != XFS_LOG) {
>  			xfs_warn(log->l_mp,
> -				"%s: invalid clientid %d op "PTR_FMT" offset 0x%lx",
> -				__func__, clientid, ophead,
> +				"%s: op %d invalid clientid %d op "PTR_FMT" offset 0x%lx",
> +				__func__, i, clientid, ophead,
>  				(unsigned long)field_offset);
> +		}
>  
>  		/* check length */
>  		p = &ophead->oh_len;
> -- 
> 2.28.0
>
Dave Chinner March 11, 2021, 4:33 a.m. UTC | #2
On Mon, Mar 08, 2021 at 06:59:32PM -0800, Darrick J. Wong wrote:
> On Fri, Mar 05, 2021 at 04:11:27PM +1100, Dave Chinner wrote:
> > From: Dave Chinner <dchinner@redhat.com>
> > 
> > Handle writing of a logvec chain into an iclog that doesn't have
> > enough space to fit it all. The iclog has already been changed to
> > WANT_SYNC by xlog_get_iclog_space(), so the entire remaining space
> > in the iclog is exclusively owned by this logvec chain.
> > 
> > The difference between the single and partial cases is that
> > we end up with partial iovec writes in the iclog and have to split
> > a log vec regions across two iclogs. The state handling for this is
> > currently awful and so we're building up the pieces needed to
> > handle this more cleanly one at a time.
> > 
> > Signed-off-by: Dave Chinner <dchinner@redhat.com>
> > ---
> >  fs/xfs/xfs_log.c | 525 ++++++++++++++++++++++-------------------------
> >  1 file changed, 251 insertions(+), 274 deletions(-)
> > 
> > diff --git a/fs/xfs/xfs_log.c b/fs/xfs/xfs_log.c
> > index 590c1e6db475..10916b99bf0f 100644
> > --- a/fs/xfs/xfs_log.c
> > +++ b/fs/xfs/xfs_log.c
> > @@ -2099,166 +2099,250 @@ xlog_print_trans(
> >  	}
> >  }
> >  
> > -static xlog_op_header_t *
> > -xlog_write_setup_ophdr(
> > -	struct xlog_op_header	*ophdr,
> > -	struct xlog_ticket	*ticket)
> > -{
> > -	ophdr->oh_clientid = XFS_TRANSACTION;
> > -	ophdr->oh_res2 = 0;
> > -	ophdr->oh_flags = 0;
> > -	return ophdr;
> > -}
> > -
> >  /*
> > - * Set up the parameters of the region copy into the log. This has
> > - * to handle region write split across multiple log buffers - this
> > - * state is kept external to this function so that this code can
> > - * be written in an obvious, self documenting manner.
> > + * Write whole log vectors into a single iclog which is guaranteed to have
> > + * either sufficient space for the entire log vector chain to be written or
> > + * exclusive access to the remaining space in the iclog.
> > + *
> > + * Return the number of iovecs and data written into the iclog, as well as
> > + * a pointer to the logvec that doesn't fit in the log (or NULL if we hit the
> > + * end of the chain.
> >   */
> > -static int
> > -xlog_write_setup_copy(
> > +static struct xfs_log_vec *
> > +xlog_write_single(
> 
> Ouch.  Could you fix the previous patch to move this new function a
> little higher in the file (like above xlog_write_setup_ophdr) so that it
> doesn't get shredded like this?

Not possible because xlog_write_setup_ophdr() is removed by this
patch. I can't help it if the diffs are unreadable - I can't really
control what git is doing here...

> > @@ -2930,7 +2906,7 @@ xlog_state_get_iclog_space(
> >  	 * xlog_write() algorithm assumes that at least 2 xlog_op_header_t's
> >  	 * can fit into remaining data section.
> >  	 */
> > -	if (iclog->ic_size - iclog->ic_offset < 2*sizeof(xlog_op_header_t)) {
> > +	if (iclog->ic_size - iclog->ic_offset < 3*sizeof(xlog_op_header_t)) {
> 
> Why does this change to 3?  Does the comment need amending?

Ah, that was to do with the avoiding the need to split the start
record/transaction header of across two iclogs. That was because the
partial copy loop didn't have special handling for start records
and so that log vector had to be wholly handled by the
xlog_write_single() loop to set the iclog flush flags.

However, with all the changes since then that have added explicit
pre-flushes before the start record is formatted and the lifting of
the iclog flush flags to the callers, we've removed all
the special optype handling in xlog_write(). Hence we no longer need
to guarantee the start record is handled by the single path, it now
can be handled by this partial path just fine. So I can revert this
hunk.

Did I mention that this code was full of all sorts of subtle corner
cases? :/

Cheers,

Dave.
Brian Foster March 18, 2021, 1:22 p.m. UTC | #3
On Fri, Mar 05, 2021 at 04:11:27PM +1100, Dave Chinner wrote:
> From: Dave Chinner <dchinner@redhat.com>
> 
> Handle writing of a logvec chain into an iclog that doesn't have
> enough space to fit it all. The iclog has already been changed to
> WANT_SYNC by xlog_get_iclog_space(), so the entire remaining space
> in the iclog is exclusively owned by this logvec chain.
> 
> The difference between the single and partial cases is that
> we end up with partial iovec writes in the iclog and have to split
> a log vec regions across two iclogs. The state handling for this is
> currently awful and so we're building up the pieces needed to
> handle this more cleanly one at a time.
> 
> Signed-off-by: Dave Chinner <dchinner@redhat.com>
> ---

FWIW, git --patience mode generates a more readable diff for this patch
than what it generates by default. I'm referring to that locally and
will try to leave feedback in the appropriate points here.

>  fs/xfs/xfs_log.c | 525 ++++++++++++++++++++++-------------------------
>  1 file changed, 251 insertions(+), 274 deletions(-)
> 
> diff --git a/fs/xfs/xfs_log.c b/fs/xfs/xfs_log.c
> index 590c1e6db475..10916b99bf0f 100644
> --- a/fs/xfs/xfs_log.c
> +++ b/fs/xfs/xfs_log.c
> @@ -2099,166 +2099,250 @@ xlog_print_trans(
>  	}
>  }
>  
> -static xlog_op_header_t *
> -xlog_write_setup_ophdr(
> -	struct xlog_op_header	*ophdr,
> -	struct xlog_ticket	*ticket)
> -{
> -	ophdr->oh_clientid = XFS_TRANSACTION;
> -	ophdr->oh_res2 = 0;
> -	ophdr->oh_flags = 0;
> -	return ophdr;
> -}
> -
>  /*
> - * Set up the parameters of the region copy into the log. This has
> - * to handle region write split across multiple log buffers - this
> - * state is kept external to this function so that this code can
> - * be written in an obvious, self documenting manner.
> + * Write whole log vectors into a single iclog which is guaranteed to have
> + * either sufficient space for the entire log vector chain to be written or
> + * exclusive access to the remaining space in the iclog.
> + *
> + * Return the number of iovecs and data written into the iclog, as well as
> + * a pointer to the logvec that doesn't fit in the log (or NULL if we hit the
> + * end of the chain.
>   */
> -static int
> -xlog_write_setup_copy(
> +static struct xfs_log_vec *
> +xlog_write_single(
> +	struct xfs_log_vec	*log_vector,

So xlog_write_single() was initially for single CIL xlog_write() calls
and now it appears to be slightly different in that it writes as many
full log vectors that fit in the current iclog and cycles through
xlog_write_partial() (and back) to process log vectors that span iclogs
differently from those that don't.

>  	struct xlog_ticket	*ticket,
> -	struct xlog_op_header	*ophdr,
> -	int			space_available,
> -	int			space_required,
> -	int			*copy_off,
> -	int			*copy_len,
> -	int			*last_was_partial_copy,
> -	int			*bytes_consumed)
> -{
> -	int			still_to_copy;
> -
> -	still_to_copy = space_required - *bytes_consumed;
> -	*copy_off = *bytes_consumed;
> -
> -	if (still_to_copy <= space_available) {
> -		/* write of region completes here */
> -		*copy_len = still_to_copy;
> -		ophdr->oh_len = cpu_to_be32(*copy_len);
> -		if (*last_was_partial_copy)
> -			ophdr->oh_flags |= (XLOG_END_TRANS|XLOG_WAS_CONT_TRANS);
> -		*last_was_partial_copy = 0;
> -		*bytes_consumed = 0;
> -		return 0;
> -	}
> -
> -	/* partial write of region, needs extra log op header reservation */
> -	*copy_len = space_available;
> -	ophdr->oh_len = cpu_to_be32(*copy_len);
> -	ophdr->oh_flags |= XLOG_CONTINUE_TRANS;
> -	if (*last_was_partial_copy)
> -		ophdr->oh_flags |= XLOG_WAS_CONT_TRANS;
> -	*bytes_consumed += *copy_len;
> -	(*last_was_partial_copy)++;
> -
> -	/* account for new log op header */
> -	ticket->t_curr_res -= sizeof(struct xlog_op_header);
> -
> -	return sizeof(struct xlog_op_header);
> -}
> -
> -static int
> -xlog_write_copy_finish(
> -	struct xlog		*log,
>  	struct xlog_in_core	*iclog,
> -	uint			flags,
> -	int			*record_cnt,
> -	int			*data_cnt,
> -	int			*partial_copy,
> -	int			*partial_copy_len,
> -	int			log_offset,
> -	struct xlog_in_core	**commit_iclog)
> +	uint32_t		*log_offset,
> +	uint32_t		*len,
> +	uint32_t		*record_cnt,
> +	uint32_t		*data_cnt)
>  {
> -	int			error;
> +	struct xfs_log_vec	*lv = log_vector;
> +	void			*ptr;
> +	int			index;
>  
> -	if (*partial_copy) {
> +	ASSERT(*log_offset + *len <= iclog->ic_size ||
> +		iclog->ic_state == XLOG_STATE_WANT_SYNC);
> +
> +	ptr = iclog->ic_datap + *log_offset;
> +	for (lv = log_vector; lv; lv = lv->lv_next) {
>  		/*
> -		 * This iclog has already been marked WANT_SYNC by
> -		 * xlog_state_get_iclog_space.
> +		 * If the entire log vec does not fit in the iclog, punt it to
> +		 * the partial copy loop which can handle this case.
>  		 */
> -		spin_lock(&log->l_icloglock);
> -		xlog_state_finish_copy(log, iclog, *record_cnt, *data_cnt);
> -		*record_cnt = 0;
> -		*data_cnt = 0;
> -		goto release_iclog;
> -	}
> +		if (lv->lv_niovecs &&
> +		    lv->lv_bytes > iclog->ic_size - *log_offset)
> +			break;
>  
> -	*partial_copy = 0;
> -	*partial_copy_len = 0;
> +		/*
> +		 * Ordered log vectors have no regions to write so this
> +		 * loop will naturally skip them.
> +		 */
> +		for (index = 0; index < lv->lv_niovecs; index++) {
> +			struct xfs_log_iovec	*reg = &lv->lv_iovecp[index];
> +			struct xlog_op_header	*ophdr = reg->i_addr;
>  
> -	if (iclog->ic_size - log_offset <= sizeof(xlog_op_header_t)) {
> -		/* no more space in this iclog - push it. */
> -		spin_lock(&log->l_icloglock);
> -		xlog_state_finish_copy(log, iclog, *record_cnt, *data_cnt);
> -		*record_cnt = 0;
> -		*data_cnt = 0;
> +			ASSERT(reg->i_len % sizeof(int32_t) == 0);
> +			ASSERT((unsigned long)ptr % sizeof(int32_t) == 0);
>  
> -		if (iclog->ic_state == XLOG_STATE_ACTIVE)
> -			xlog_state_switch_iclogs(log, iclog, 0);
> -		else
> -			ASSERT(iclog->ic_state == XLOG_STATE_WANT_SYNC ||
> -			       iclog->ic_state == XLOG_STATE_IOERROR);
> -		if (!commit_iclog)
> -			goto release_iclog;
> -		spin_unlock(&log->l_icloglock);
> -		ASSERT(flags & XLOG_COMMIT_TRANS);
> -		*commit_iclog = iclog;
> +			ophdr->oh_tid = cpu_to_be32(ticket->t_tid);
> +			ophdr->oh_len = cpu_to_be32(reg->i_len -
> +						sizeof(struct xlog_op_header));
> +			memcpy(ptr, reg->i_addr, reg->i_len);
> +			xlog_write_adv_cnt(&ptr, len, log_offset, reg->i_len);
> +			(*record_cnt)++;
> +			*data_cnt += reg->i_len;
> +		}
>  	}
> +	ASSERT(*len == 0 || lv);
> +	return lv;
> +}
>  
> -	return 0;
> +static int
> +xlog_write_get_more_iclog_space(
> +	struct xlog		*log,
> +	struct xlog_ticket	*ticket,
> +	struct xlog_in_core	**iclogp,
> +	uint32_t		*log_offset,
> +	uint32_t		len,
> +	uint32_t		*record_cnt,
> +	uint32_t		*data_cnt,
> +	int			*contwr)
> +{
> +	struct xlog_in_core	*iclog = *iclogp;
> +	int			error;
>  
> -release_iclog:
> +	spin_lock(&log->l_icloglock);
> +	xlog_state_finish_copy(log, iclog, *record_cnt, *data_cnt);
> +	ASSERT(iclog->ic_state == XLOG_STATE_WANT_SYNC ||
> +	       iclog->ic_state == XLOG_STATE_IOERROR);
>  	error = xlog_state_release_iclog(log, iclog);
>  	spin_unlock(&log->l_icloglock);
> -	return error;
> +	if (error)
> +		return error;
> +
> +	error = xlog_state_get_iclog_space(log, len, &iclog,
> +				ticket, contwr, log_offset);
> +	if (error)
> +		return error;
> +	*record_cnt = 0;
> +	*data_cnt = 0;
> +	*iclogp = iclog;
> +	return 0;
>  }
>  
>  /*
> - * Write log vectors into a single iclog which is guaranteed by the caller
> - * to have enough space to write the entire log vector into. Return the number
> - * of log vectors written into the iclog.
> + * Write log vectors into a single iclog which is smaller than the current chain
> + * length. We write until we cannot fit a full record into the remaining space
> + * and then stop. We return the log vector that is to be written that cannot
> + * wholly fit in the iclog.
>   */
> -static int
> -xlog_write_single(
> +static struct xfs_log_vec *
> +xlog_write_partial(
> +	struct xlog		*log,
>  	struct xfs_log_vec	*log_vector,
>  	struct xlog_ticket	*ticket,
> -	struct xlog_in_core	*iclog,
> -	uint32_t		log_offset,
> -	uint32_t		len)
> +	struct xlog_in_core	**iclogp,
> +	uint32_t		*log_offset,
> +	uint32_t		*len,
> +	uint32_t		*record_cnt,
> +	uint32_t		*data_cnt,
> +	int			*contwr)
>  {
> +	struct xlog_in_core	*iclog = *iclogp;
>  	struct xfs_log_vec	*lv = log_vector;

The log_vector -> lv assignment seems spurious at this point since this
function only processes lv and returns the next.

> +	struct xfs_log_iovec	*reg;
> +	struct xlog_op_header	*ophdr;
>  	void			*ptr;
>  	int			index = 0;
> -	int			record_cnt = 0;
> +	uint32_t		rlen;
> +	int			error;
>  
> -	ASSERT(log_offset + len <= iclog->ic_size);
> +	/* walk the logvec, copying until we run out of space in the iclog */
> +	ptr = iclog->ic_datap + *log_offset;
> +	for (index = 0; index < lv->lv_niovecs; index++) {
> +		uint32_t	reg_offset = 0;
> +
> +		reg = &lv->lv_iovecp[index];
> +		ASSERT(reg->i_len % sizeof(int32_t) == 0);
>  
> -	ptr = iclog->ic_datap + log_offset;
> -	for (lv = log_vector; lv; lv = lv->lv_next) {
>  		/*
> -		 * Ordered log vectors have no regions to write so this
> -		 * loop will naturally skip them.
> +		 * The first region of a continuation must have a non-zero
> +		 * length otherwise log recovery will just skip over it and
> +		 * start recovering from the next opheader it finds. Because we
> +		 * mark the next opheader as a continuation, recovery will then
> +		 * incorrectly add the continuation to the previous region and
> +		 * that breaks stuff.
> +		 *
> +		 * Hence if there isn't space for region data after the
> +		 * opheader, then we need to start afresh with a new iclog.
>  		 */
> -		for (index = 0; index < lv->lv_niovecs; index++) {
> -			struct xfs_log_iovec	*reg = &lv->lv_iovecp[index];
> -			struct xlog_op_header	*ophdr = reg->i_addr;
> +		if (iclog->ic_size - *log_offset <=
> +					sizeof(struct xlog_op_header)) {
> +			error = xlog_write_get_more_iclog_space(log, ticket,
> +					&iclog, log_offset, *len, record_cnt,
> +					data_cnt, contwr);
> +			if (error)
> +				return ERR_PTR(error);
> +			ptr = iclog->ic_datap + *log_offset;
> +		}
>  
> -			ASSERT(reg->i_len % sizeof(int32_t) == 0);
> -			ASSERT((unsigned long)ptr % sizeof(int32_t) == 0);
> +		ophdr = reg->i_addr;
> +		rlen = min_t(uint32_t, reg->i_len, iclog->ic_size - *log_offset);
> +
> +		ophdr->oh_tid = cpu_to_be32(ticket->t_tid);
> +		ophdr->oh_len = cpu_to_be32(rlen - sizeof(struct xlog_op_header));
> +		if (rlen != reg->i_len)
> +			ophdr->oh_flags |= XLOG_CONTINUE_TRANS;
>  
> +		ASSERT((unsigned long)ptr % sizeof(int32_t) == 0);
> +		xlog_verify_dest_ptr(log, ptr);
> +		memcpy(ptr, reg->i_addr, rlen);
> +		xlog_write_adv_cnt(&ptr, len, log_offset, rlen);
> +		(*record_cnt)++;
> +		*data_cnt += rlen;
> +

		/* if we fit the full region, jump to the next */

> +		if (rlen == reg->i_len)
> +			continue;
> +
> +		/*
> +		 * We now have a partially written iovec, but it can span
> +		 * multiple iclogs so we loop here. First we release the iclog
> +		 * we currently have, then we get a new iclog and add a new
> +		 * opheader. Then we continue copying from where we were until
> +		 * we either complete the iovec or fill the iclog. If we
> +		 * complete the iovec, then we increment the index and go right
> +		 * back to the top of the outer loop. if we fill the iclog, we
> +		 * run the inner loop again.
> +		 *
> +		 * This is complicated by the tail of a region using all the
> +		 * space in an iclog and hence requiring us to release the iclog
> +		 * and get a new one before returning to the outer loop. We must
> +		 * always guarantee that we exit this inner loop with at least
> +		 * space for log transaction opheaders left in the current
> +		 * iclog, hence we cannot just terminate the loop at the end
> +		 * of the of the continuation. So we loop while there is no
> +		 * space left in the current iclog, and check for the end of the
> +		 * continuation after getting a new iclog.
> +		 */

Ok, so we land in this function if an lv spans an iclog boundary. The
upper loop writes full vectors until we hit said iclog boundary, then we
fall into the inner loop...

> +		do {
> +			/*
> +			 * Account for the continuation opheader before we get
> +			 * a new iclog. This is necessary so that we reserve
> +			 * space in the iclog for it.
> +			 */
> +			if (ophdr->oh_flags & XLOG_CONTINUE_TRANS) {

(Is this ever not true here?)

> +				*len += sizeof(struct xlog_op_header);
> +				ticket->t_curr_res -= sizeof(struct xlog_op_header);
> +			}
> +			error = xlog_write_get_more_iclog_space(log, ticket,
> +					&iclog, log_offset, *len, record_cnt,
> +					data_cnt, contwr);
> +			if (error)
> +				return ERR_PTR(error);
> +			ptr = iclog->ic_datap + *log_offset;
> +
> +			ophdr = ptr;
>  			ophdr->oh_tid = cpu_to_be32(ticket->t_tid);
> -			ophdr->oh_len = cpu_to_be32(reg->i_len -
> +			ophdr->oh_clientid = XFS_TRANSACTION;
> +			ophdr->oh_res2 = 0;
> +			ophdr->oh_flags = XLOG_WAS_CONT_TRANS;
> +
> +			xlog_write_adv_cnt(&ptr, len, log_offset,
>  						sizeof(struct xlog_op_header));
> -			memcpy(ptr, reg->i_addr, reg->i_len);
> -			xlog_write_adv_cnt(&ptr, &len, &log_offset, reg->i_len);
> -			record_cnt++;
> -		}
> +			*data_cnt += sizeof(struct xlog_op_header);
> +

... which switches to the next iclog, writes the continuation header...

> +			/*
> +			 * If rlen fits in the iclog, then end the region
> +			 * continuation. Otherwise we're going around again.
> +			 */
> +			reg_offset += rlen;
> +			rlen = reg->i_len - reg_offset;
> +			if (rlen <= iclog->ic_size - *log_offset)
> +				ophdr->oh_flags |= XLOG_END_TRANS;
> +			else
> +				ophdr->oh_flags |= XLOG_CONTINUE_TRANS;
> +
> +			rlen = min_t(uint32_t, rlen, iclog->ic_size - *log_offset);
> +			ophdr->oh_len = cpu_to_be32(rlen);
> +
> +			xlog_verify_dest_ptr(log, ptr);
> +			memcpy(ptr, reg->i_addr + reg_offset, rlen);
> +			xlog_write_adv_cnt(&ptr, len, log_offset, rlen);
> +			(*record_cnt)++;
> +			*data_cnt += rlen;
> +
> +		} while (ophdr->oh_flags & XLOG_CONTINUE_TRANS);

... writes more of the region (iclog space permitting), and then
determines whether we need further continuations (and partial writes of
the same region) or can move onto the next region, until we're done with
the lv.

I think I follow the high level flow and it seems reasonable from a
functional standpoint, but this also seems like quite a bit of churn for
not much reduction in overall complexity. The higher level loop is much
more simple and I think the per lv/vector iteration is an improvement,
but we also seem to have duplicate functionality throughout the updated
code and have introduced new forms of complexity around the state
expectations for the transitions between the different write modes and
between each write mode and the higher level loop.

I.e., xlog_write_single() implements a straighforward loop to write out
full log vectors. That seems fine, but the outer loop of
xlog_write_partial() reimplements nearly the same per-region
functionality with some added flexibility to handle op header flags and
the special iclog processing associated with the continuation case. The
inner loop factors out the continuation iclog management bits and op
header injection, which I think is an improvement, but then duplicates
region copying (yet again) pretty much only to implement partial copies,
which really just involves offset management (i.e., fairly trivial
relative to the broader complexity of the function).

I dunno. I'd certainly need to stare more at this to cover all of the
details, but given the amount of swizzling going on in a single patch
I'm kind of wondering if/why we couldn't land on a single iterator in
the spirit of xlog_write_partial() in that it primarily iterates on
regions and factors out the grotty reservation and continuation
management bits, but doesn't unroll as much and leave so much duplicate
functionality around.

For example, it looks to me that xlog_write_partial() almost nearly
already supports a high level algorithm along the lines of the following
(pseudocode):

xlog_write(len)
{
	get_iclog_space(len)

	for_each_lv() {
		for_each_reg() {
			reg_offset = 0;
cont_write:
			/* write as much as will fit in the iclog, return count,
			 * and set ophdr cont flag based on write result */
			reg_offset += write_region(reg, &len, &reg_offset, ophdr, ...);

			/* handle continuation writes */
			if (reg_offset != reg->i_len) {
				get_more_iclog_space(len);
				/* stamp a WAS_CONT op hdr, set END if rlen fits
				 * into new space, then continue with the same region */
				stamp_cont_op_hdr();
				goto cont_write;
			}

			if (need_more_iclog_space(len))
				get_more_iclog_space(len);
		}
	}
}

That puts the whole thing back into a single high level walk and thus
reintroduces the need for some of the continuation vs. non-continuation
tracking wrt to the op header and iclog, but ISTM that complexity can be
managed by the continuation abstraction you've already started to
introduce (as opposed to the current scheme of conditionally
accumulating data_cnt). It might even be fine to dump some of the
requisite state into a context struct to carry between iclog reservation
and copy finish processing rather than pass around so many independent
and poorly named variables like the current upstream implementation
does, but that's probably getting too deep into the weeds.

FWIW, I can also see an approach of moving from the implementation in
this patch toward something like the above, but I'm not sure I'd want to
subject to the upstream code to that process...

Brian

>  	}
> -	ASSERT(len == 0);
> -	return record_cnt;
> -}
>  
> +	/*
> +	 * No more iovecs remain in this logvec so return the next log vec to
> +	 * the caller so it can go back to fast path copying.
> +	 */
> +	*iclogp = iclog;
> +	return lv->lv_next;
> +}
>  
>  /*
>   * Write some region out to in-core log
> @@ -2312,14 +2396,11 @@ xlog_write(
>  {
>  	struct xlog_in_core	*iclog = NULL;
>  	struct xfs_log_vec	*lv = log_vector;
> -	struct xfs_log_iovec	*vecp = lv->lv_iovecp;
> -	int			index = 0;
> -	int			partial_copy = 0;
> -	int			partial_copy_len = 0;
>  	int			contwr = 0;
>  	int			record_cnt = 0;
>  	int			data_cnt = 0;
>  	int			error = 0;
> +	int			log_offset;
>  
>  	if (ticket->t_curr_res < 0) {
>  		xfs_alert_tag(log->l_mp, XFS_PTAG_LOGRES,
> @@ -2328,157 +2409,52 @@ xlog_write(
>  		xfs_force_shutdown(log->l_mp, SHUTDOWN_LOG_IO_ERROR);
>  	}
>  
> -	if (start_lsn)
> -		*start_lsn = 0;
> -	while (lv && (!lv->lv_niovecs || index < lv->lv_niovecs)) {
> -		void		*ptr;
> -		int		log_offset;
> -
> -		error = xlog_state_get_iclog_space(log, len, &iclog, ticket,
> -						   &contwr, &log_offset);
> -		if (error)
> -			return error;
> -
> -		ASSERT(log_offset <= iclog->ic_size - 1);
> +	error = xlog_state_get_iclog_space(log, len, &iclog, ticket,
> +					   &contwr, &log_offset);
> +	if (error)
> +		return error;
>  
> -		/* Start_lsn is the first lsn written to. */
> -		if (start_lsn && !*start_lsn)
> -			*start_lsn = be64_to_cpu(iclog->ic_header.h_lsn);
> +	/* start_lsn is the LSN of the first iclog written to. */
> +	if (start_lsn)
> +		*start_lsn = be64_to_cpu(iclog->ic_header.h_lsn);
>  
> -		/*
> -		 * iclogs containing commit records or unmount records need
> -		 * to issue ordering cache flushes and commit immediately
> -		 * to stable storage to guarantee journal vs metadata ordering
> -		 * is correctly maintained in the storage media.
> -		 */
> -		if (optype & (XLOG_COMMIT_TRANS | XLOG_UNMOUNT_TRANS)) {
> -			iclog->ic_flags |= (XLOG_ICL_NEED_FLUSH |
> -						XLOG_ICL_NEED_FUA);
> -		}
> +	/*
> +	 * iclogs containing commit records or unmount records need
> +	 * to issue ordering cache flushes and commit immediately
> +	 * to stable storage to guarantee journal vs metadata ordering
> +	 * is correctly maintained in the storage media. This will always
> +	 * fit in the iclog we have been already been passed.
> +	 */
> +	if (optype & (XLOG_COMMIT_TRANS | XLOG_UNMOUNT_TRANS)) {
> +		iclog->ic_flags |= (XLOG_ICL_NEED_FLUSH | XLOG_ICL_NEED_FUA);
> +		ASSERT(!contwr);
> +	}
>  
> -		/* If this is a single iclog write, go fast... */
> -		if (!contwr && lv == log_vector) {
> -			record_cnt = xlog_write_single(lv, ticket, iclog,
> -						log_offset, len);
> -			len = 0;
> -			data_cnt = len;
> +	while (lv) {
> +		lv = xlog_write_single(lv, ticket, iclog, &log_offset,
> +					&len, &record_cnt, &data_cnt);
> +		if (!lv)
>  			break;
> -		}
> -
> -		/*
> -		 * This loop writes out as many regions as can fit in the amount
> -		 * of space which was allocated by xlog_state_get_iclog_space().
> -		 */
> -		ptr = iclog->ic_datap + log_offset;
> -		while (lv && (!lv->lv_niovecs || index < lv->lv_niovecs)) {
> -			struct xfs_log_iovec	*reg;
> -			struct xlog_op_header	*ophdr;
> -			int			copy_len;
> -			int			copy_off;
> -			bool			ordered = false;
> -			bool			added_ophdr = false;
> -
> -			/* ordered log vectors have no regions to write */
> -			if (lv->lv_buf_len == XFS_LOG_VEC_ORDERED) {
> -				ASSERT(lv->lv_niovecs == 0);
> -				ordered = true;
> -				goto next_lv;
> -			}
> -
> -			reg = &vecp[index];
> -			ASSERT(reg->i_len % sizeof(int32_t) == 0);
> -			ASSERT((unsigned long)ptr % sizeof(int32_t) == 0);
> -
> -			/*
> -			 * Regions always have their ophdr at the start of the
> -			 * region, except for:
> -			 * - a transaction start which has a start record ophdr
> -			 *   before the first region ophdr; and
> -			 * - the previous region didn't fully fit into an iclog
> -			 *   so needs a continuation ophdr to prepend the region
> -			 *   in this new iclog.
> -			 */
> -			ophdr = reg->i_addr;
> -			if (optype && index) {
> -				optype &= ~XLOG_START_TRANS;
> -			} else if (partial_copy) {
> -                                ophdr = xlog_write_setup_ophdr(ptr, ticket);
> -				xlog_write_adv_cnt(&ptr, &len, &log_offset,
> -					   sizeof(struct xlog_op_header));
> -				added_ophdr = true;
> -			}
> -			ophdr->oh_tid = cpu_to_be32(ticket->t_tid);
> -
> -			len += xlog_write_setup_copy(ticket, ophdr,
> -						     iclog->ic_size-log_offset,
> -						     reg->i_len,
> -						     &copy_off, &copy_len,
> -						     &partial_copy,
> -						     &partial_copy_len);
> -			xlog_verify_dest_ptr(log, ptr);
> -
>  
> -			/*
> -			 * Wart: need to update length in embedded ophdr not
> -			 * to include it's own length.
> -			 */
> -			if (!added_ophdr) {
> -				ophdr->oh_len = cpu_to_be32(copy_len -
> -						sizeof(struct xlog_op_header));
> -			}
> -
> -			ASSERT(copy_len > 0);
> -			memcpy(ptr, reg->i_addr + copy_off, copy_len);
> -			xlog_write_adv_cnt(&ptr, &len, &log_offset, copy_len);
> -
> -			if (added_ophdr)
> -				copy_len += sizeof(struct xlog_op_header);
> -			record_cnt++;
> -			data_cnt += contwr ? copy_len : 0;
> -
> -			error = xlog_write_copy_finish(log, iclog, optype,
> -						       &record_cnt, &data_cnt,
> -						       &partial_copy,
> -						       &partial_copy_len,
> -						       log_offset,
> -						       commit_iclog);
> -			if (error)
> -				return error;
> -
> -			/*
> -			 * if we had a partial copy, we need to get more iclog
> -			 * space but we don't want to increment the region
> -			 * index because there is still more is this region to
> -			 * write.
> -			 *
> -			 * If we completed writing this region, and we flushed
> -			 * the iclog (indicated by resetting of the record
> -			 * count), then we also need to get more log space. If
> -			 * this was the last record, though, we are done and
> -			 * can just return.
> -			 */
> -			if (partial_copy)
> -				break;
> -
> -			if (++index == lv->lv_niovecs) {
> -next_lv:
> -				lv = lv->lv_next;
> -				index = 0;
> -				if (lv)
> -					vecp = lv->lv_iovecp;
> -			}
> -			if (record_cnt == 0 && !ordered) {
> -				if (!lv)
> -					return 0;
> -				break;
> -			}
> +		ASSERT(!(optype & (XLOG_COMMIT_TRANS | XLOG_UNMOUNT_TRANS)));
> +		lv = xlog_write_partial(log, lv, ticket, &iclog, &log_offset,
> +					&len, &record_cnt, &data_cnt, &contwr);
> +		if (IS_ERR_OR_NULL(lv)) {
> +			error = PTR_ERR_OR_ZERO(lv);
> +			break;
>  		}
>  	}
> +	ASSERT((len == 0 && !lv) || error);
>  
> -	ASSERT(len == 0);
> -
> +	/*
> +	 * We've already been guaranteed that the last writes will fit inside
> +	 * the current iclog, and hence it will already have the space used by
> +	 * those writes accounted to it. Hence we do not need to update the
> +	 * iclog with the number of bytes written here.
> +	 */
> +	ASSERT(!contwr || XLOG_FORCED_SHUTDOWN(log));
>  	spin_lock(&log->l_icloglock);
> -	xlog_state_finish_copy(log, iclog, record_cnt, data_cnt);
> +	xlog_state_finish_copy(log, iclog, record_cnt, 0);
>  	if (commit_iclog) {
>  		ASSERT(optype & XLOG_COMMIT_TRANS);
>  		*commit_iclog = iclog;
> @@ -2930,7 +2906,7 @@ xlog_state_get_iclog_space(
>  	 * xlog_write() algorithm assumes that at least 2 xlog_op_header_t's
>  	 * can fit into remaining data section.
>  	 */
> -	if (iclog->ic_size - iclog->ic_offset < 2*sizeof(xlog_op_header_t)) {
> +	if (iclog->ic_size - iclog->ic_offset < 3*sizeof(xlog_op_header_t)) {
>  		int		error = 0;
>  
>  		xlog_state_switch_iclogs(log, iclog, iclog->ic_size);
> @@ -3633,11 +3609,12 @@ xlog_verify_iclog(
>  					iclog->ic_header.h_cycle_data[idx]);
>  			}
>  		}
> -		if (clientid != XFS_TRANSACTION && clientid != XFS_LOG)
> +		if (clientid != XFS_TRANSACTION && clientid != XFS_LOG) {
>  			xfs_warn(log->l_mp,
> -				"%s: invalid clientid %d op "PTR_FMT" offset 0x%lx",
> -				__func__, clientid, ophead,
> +				"%s: op %d invalid clientid %d op "PTR_FMT" offset 0x%lx",
> +				__func__, i, clientid, ophead,
>  				(unsigned long)field_offset);
> +		}
>  
>  		/* check length */
>  		p = &ophead->oh_len;
> -- 
> 2.28.0
>
diff mbox series

Patch

diff --git a/fs/xfs/xfs_log.c b/fs/xfs/xfs_log.c
index 590c1e6db475..10916b99bf0f 100644
--- a/fs/xfs/xfs_log.c
+++ b/fs/xfs/xfs_log.c
@@ -2099,166 +2099,250 @@  xlog_print_trans(
 	}
 }
 
-static xlog_op_header_t *
-xlog_write_setup_ophdr(
-	struct xlog_op_header	*ophdr,
-	struct xlog_ticket	*ticket)
-{
-	ophdr->oh_clientid = XFS_TRANSACTION;
-	ophdr->oh_res2 = 0;
-	ophdr->oh_flags = 0;
-	return ophdr;
-}
-
 /*
- * Set up the parameters of the region copy into the log. This has
- * to handle region write split across multiple log buffers - this
- * state is kept external to this function so that this code can
- * be written in an obvious, self documenting manner.
+ * Write whole log vectors into a single iclog which is guaranteed to have
+ * either sufficient space for the entire log vector chain to be written or
+ * exclusive access to the remaining space in the iclog.
+ *
+ * Return the number of iovecs and data written into the iclog, as well as
+ * a pointer to the logvec that doesn't fit in the log (or NULL if we hit the
+ * end of the chain.
  */
-static int
-xlog_write_setup_copy(
+static struct xfs_log_vec *
+xlog_write_single(
+	struct xfs_log_vec	*log_vector,
 	struct xlog_ticket	*ticket,
-	struct xlog_op_header	*ophdr,
-	int			space_available,
-	int			space_required,
-	int			*copy_off,
-	int			*copy_len,
-	int			*last_was_partial_copy,
-	int			*bytes_consumed)
-{
-	int			still_to_copy;
-
-	still_to_copy = space_required - *bytes_consumed;
-	*copy_off = *bytes_consumed;
-
-	if (still_to_copy <= space_available) {
-		/* write of region completes here */
-		*copy_len = still_to_copy;
-		ophdr->oh_len = cpu_to_be32(*copy_len);
-		if (*last_was_partial_copy)
-			ophdr->oh_flags |= (XLOG_END_TRANS|XLOG_WAS_CONT_TRANS);
-		*last_was_partial_copy = 0;
-		*bytes_consumed = 0;
-		return 0;
-	}
-
-	/* partial write of region, needs extra log op header reservation */
-	*copy_len = space_available;
-	ophdr->oh_len = cpu_to_be32(*copy_len);
-	ophdr->oh_flags |= XLOG_CONTINUE_TRANS;
-	if (*last_was_partial_copy)
-		ophdr->oh_flags |= XLOG_WAS_CONT_TRANS;
-	*bytes_consumed += *copy_len;
-	(*last_was_partial_copy)++;
-
-	/* account for new log op header */
-	ticket->t_curr_res -= sizeof(struct xlog_op_header);
-
-	return sizeof(struct xlog_op_header);
-}
-
-static int
-xlog_write_copy_finish(
-	struct xlog		*log,
 	struct xlog_in_core	*iclog,
-	uint			flags,
-	int			*record_cnt,
-	int			*data_cnt,
-	int			*partial_copy,
-	int			*partial_copy_len,
-	int			log_offset,
-	struct xlog_in_core	**commit_iclog)
+	uint32_t		*log_offset,
+	uint32_t		*len,
+	uint32_t		*record_cnt,
+	uint32_t		*data_cnt)
 {
-	int			error;
+	struct xfs_log_vec	*lv = log_vector;
+	void			*ptr;
+	int			index;
 
-	if (*partial_copy) {
+	ASSERT(*log_offset + *len <= iclog->ic_size ||
+		iclog->ic_state == XLOG_STATE_WANT_SYNC);
+
+	ptr = iclog->ic_datap + *log_offset;
+	for (lv = log_vector; lv; lv = lv->lv_next) {
 		/*
-		 * This iclog has already been marked WANT_SYNC by
-		 * xlog_state_get_iclog_space.
+		 * If the entire log vec does not fit in the iclog, punt it to
+		 * the partial copy loop which can handle this case.
 		 */
-		spin_lock(&log->l_icloglock);
-		xlog_state_finish_copy(log, iclog, *record_cnt, *data_cnt);
-		*record_cnt = 0;
-		*data_cnt = 0;
-		goto release_iclog;
-	}
+		if (lv->lv_niovecs &&
+		    lv->lv_bytes > iclog->ic_size - *log_offset)
+			break;
 
-	*partial_copy = 0;
-	*partial_copy_len = 0;
+		/*
+		 * Ordered log vectors have no regions to write so this
+		 * loop will naturally skip them.
+		 */
+		for (index = 0; index < lv->lv_niovecs; index++) {
+			struct xfs_log_iovec	*reg = &lv->lv_iovecp[index];
+			struct xlog_op_header	*ophdr = reg->i_addr;
 
-	if (iclog->ic_size - log_offset <= sizeof(xlog_op_header_t)) {
-		/* no more space in this iclog - push it. */
-		spin_lock(&log->l_icloglock);
-		xlog_state_finish_copy(log, iclog, *record_cnt, *data_cnt);
-		*record_cnt = 0;
-		*data_cnt = 0;
+			ASSERT(reg->i_len % sizeof(int32_t) == 0);
+			ASSERT((unsigned long)ptr % sizeof(int32_t) == 0);
 
-		if (iclog->ic_state == XLOG_STATE_ACTIVE)
-			xlog_state_switch_iclogs(log, iclog, 0);
-		else
-			ASSERT(iclog->ic_state == XLOG_STATE_WANT_SYNC ||
-			       iclog->ic_state == XLOG_STATE_IOERROR);
-		if (!commit_iclog)
-			goto release_iclog;
-		spin_unlock(&log->l_icloglock);
-		ASSERT(flags & XLOG_COMMIT_TRANS);
-		*commit_iclog = iclog;
+			ophdr->oh_tid = cpu_to_be32(ticket->t_tid);
+			ophdr->oh_len = cpu_to_be32(reg->i_len -
+						sizeof(struct xlog_op_header));
+			memcpy(ptr, reg->i_addr, reg->i_len);
+			xlog_write_adv_cnt(&ptr, len, log_offset, reg->i_len);
+			(*record_cnt)++;
+			*data_cnt += reg->i_len;
+		}
 	}
+	ASSERT(*len == 0 || lv);
+	return lv;
+}
 
-	return 0;
+static int
+xlog_write_get_more_iclog_space(
+	struct xlog		*log,
+	struct xlog_ticket	*ticket,
+	struct xlog_in_core	**iclogp,
+	uint32_t		*log_offset,
+	uint32_t		len,
+	uint32_t		*record_cnt,
+	uint32_t		*data_cnt,
+	int			*contwr)
+{
+	struct xlog_in_core	*iclog = *iclogp;
+	int			error;
 
-release_iclog:
+	spin_lock(&log->l_icloglock);
+	xlog_state_finish_copy(log, iclog, *record_cnt, *data_cnt);
+	ASSERT(iclog->ic_state == XLOG_STATE_WANT_SYNC ||
+	       iclog->ic_state == XLOG_STATE_IOERROR);
 	error = xlog_state_release_iclog(log, iclog);
 	spin_unlock(&log->l_icloglock);
-	return error;
+	if (error)
+		return error;
+
+	error = xlog_state_get_iclog_space(log, len, &iclog,
+				ticket, contwr, log_offset);
+	if (error)
+		return error;
+	*record_cnt = 0;
+	*data_cnt = 0;
+	*iclogp = iclog;
+	return 0;
 }
 
 /*
- * Write log vectors into a single iclog which is guaranteed by the caller
- * to have enough space to write the entire log vector into. Return the number
- * of log vectors written into the iclog.
+ * Write log vectors into a single iclog which is smaller than the current chain
+ * length. We write until we cannot fit a full record into the remaining space
+ * and then stop. We return the log vector that is to be written that cannot
+ * wholly fit in the iclog.
  */
-static int
-xlog_write_single(
+static struct xfs_log_vec *
+xlog_write_partial(
+	struct xlog		*log,
 	struct xfs_log_vec	*log_vector,
 	struct xlog_ticket	*ticket,
-	struct xlog_in_core	*iclog,
-	uint32_t		log_offset,
-	uint32_t		len)
+	struct xlog_in_core	**iclogp,
+	uint32_t		*log_offset,
+	uint32_t		*len,
+	uint32_t		*record_cnt,
+	uint32_t		*data_cnt,
+	int			*contwr)
 {
+	struct xlog_in_core	*iclog = *iclogp;
 	struct xfs_log_vec	*lv = log_vector;
+	struct xfs_log_iovec	*reg;
+	struct xlog_op_header	*ophdr;
 	void			*ptr;
 	int			index = 0;
-	int			record_cnt = 0;
+	uint32_t		rlen;
+	int			error;
 
-	ASSERT(log_offset + len <= iclog->ic_size);
+	/* walk the logvec, copying until we run out of space in the iclog */
+	ptr = iclog->ic_datap + *log_offset;
+	for (index = 0; index < lv->lv_niovecs; index++) {
+		uint32_t	reg_offset = 0;
+
+		reg = &lv->lv_iovecp[index];
+		ASSERT(reg->i_len % sizeof(int32_t) == 0);
 
-	ptr = iclog->ic_datap + log_offset;
-	for (lv = log_vector; lv; lv = lv->lv_next) {
 		/*
-		 * Ordered log vectors have no regions to write so this
-		 * loop will naturally skip them.
+		 * The first region of a continuation must have a non-zero
+		 * length otherwise log recovery will just skip over it and
+		 * start recovering from the next opheader it finds. Because we
+		 * mark the next opheader as a continuation, recovery will then
+		 * incorrectly add the continuation to the previous region and
+		 * that breaks stuff.
+		 *
+		 * Hence if there isn't space for region data after the
+		 * opheader, then we need to start afresh with a new iclog.
 		 */
-		for (index = 0; index < lv->lv_niovecs; index++) {
-			struct xfs_log_iovec	*reg = &lv->lv_iovecp[index];
-			struct xlog_op_header	*ophdr = reg->i_addr;
+		if (iclog->ic_size - *log_offset <=
+					sizeof(struct xlog_op_header)) {
+			error = xlog_write_get_more_iclog_space(log, ticket,
+					&iclog, log_offset, *len, record_cnt,
+					data_cnt, contwr);
+			if (error)
+				return ERR_PTR(error);
+			ptr = iclog->ic_datap + *log_offset;
+		}
 
-			ASSERT(reg->i_len % sizeof(int32_t) == 0);
-			ASSERT((unsigned long)ptr % sizeof(int32_t) == 0);
+		ophdr = reg->i_addr;
+		rlen = min_t(uint32_t, reg->i_len, iclog->ic_size - *log_offset);
+
+		ophdr->oh_tid = cpu_to_be32(ticket->t_tid);
+		ophdr->oh_len = cpu_to_be32(rlen - sizeof(struct xlog_op_header));
+		if (rlen != reg->i_len)
+			ophdr->oh_flags |= XLOG_CONTINUE_TRANS;
 
+		ASSERT((unsigned long)ptr % sizeof(int32_t) == 0);
+		xlog_verify_dest_ptr(log, ptr);
+		memcpy(ptr, reg->i_addr, rlen);
+		xlog_write_adv_cnt(&ptr, len, log_offset, rlen);
+		(*record_cnt)++;
+		*data_cnt += rlen;
+
+		if (rlen == reg->i_len)
+			continue;
+
+		/*
+		 * We now have a partially written iovec, but it can span
+		 * multiple iclogs so we loop here. First we release the iclog
+		 * we currently have, then we get a new iclog and add a new
+		 * opheader. Then we continue copying from where we were until
+		 * we either complete the iovec or fill the iclog. If we
+		 * complete the iovec, then we increment the index and go right
+		 * back to the top of the outer loop. if we fill the iclog, we
+		 * run the inner loop again.
+		 *
+		 * This is complicated by the tail of a region using all the
+		 * space in an iclog and hence requiring us to release the iclog
+		 * and get a new one before returning to the outer loop. We must
+		 * always guarantee that we exit this inner loop with at least
+		 * space for log transaction opheaders left in the current
+		 * iclog, hence we cannot just terminate the loop at the end
+		 * of the of the continuation. So we loop while there is no
+		 * space left in the current iclog, and check for the end of the
+		 * continuation after getting a new iclog.
+		 */
+		do {
+			/*
+			 * Account for the continuation opheader before we get
+			 * a new iclog. This is necessary so that we reserve
+			 * space in the iclog for it.
+			 */
+			if (ophdr->oh_flags & XLOG_CONTINUE_TRANS) {
+				*len += sizeof(struct xlog_op_header);
+				ticket->t_curr_res -= sizeof(struct xlog_op_header);
+			}
+			error = xlog_write_get_more_iclog_space(log, ticket,
+					&iclog, log_offset, *len, record_cnt,
+					data_cnt, contwr);
+			if (error)
+				return ERR_PTR(error);
+			ptr = iclog->ic_datap + *log_offset;
+
+			ophdr = ptr;
 			ophdr->oh_tid = cpu_to_be32(ticket->t_tid);
-			ophdr->oh_len = cpu_to_be32(reg->i_len -
+			ophdr->oh_clientid = XFS_TRANSACTION;
+			ophdr->oh_res2 = 0;
+			ophdr->oh_flags = XLOG_WAS_CONT_TRANS;
+
+			xlog_write_adv_cnt(&ptr, len, log_offset,
 						sizeof(struct xlog_op_header));
-			memcpy(ptr, reg->i_addr, reg->i_len);
-			xlog_write_adv_cnt(&ptr, &len, &log_offset, reg->i_len);
-			record_cnt++;
-		}
+			*data_cnt += sizeof(struct xlog_op_header);
+
+			/*
+			 * If rlen fits in the iclog, then end the region
+			 * continuation. Otherwise we're going around again.
+			 */
+			reg_offset += rlen;
+			rlen = reg->i_len - reg_offset;
+			if (rlen <= iclog->ic_size - *log_offset)
+				ophdr->oh_flags |= XLOG_END_TRANS;
+			else
+				ophdr->oh_flags |= XLOG_CONTINUE_TRANS;
+
+			rlen = min_t(uint32_t, rlen, iclog->ic_size - *log_offset);
+			ophdr->oh_len = cpu_to_be32(rlen);
+
+			xlog_verify_dest_ptr(log, ptr);
+			memcpy(ptr, reg->i_addr + reg_offset, rlen);
+			xlog_write_adv_cnt(&ptr, len, log_offset, rlen);
+			(*record_cnt)++;
+			*data_cnt += rlen;
+
+		} while (ophdr->oh_flags & XLOG_CONTINUE_TRANS);
 	}
-	ASSERT(len == 0);
-	return record_cnt;
-}
 
+	/*
+	 * No more iovecs remain in this logvec so return the next log vec to
+	 * the caller so it can go back to fast path copying.
+	 */
+	*iclogp = iclog;
+	return lv->lv_next;
+}
 
 /*
  * Write some region out to in-core log
@@ -2312,14 +2396,11 @@  xlog_write(
 {
 	struct xlog_in_core	*iclog = NULL;
 	struct xfs_log_vec	*lv = log_vector;
-	struct xfs_log_iovec	*vecp = lv->lv_iovecp;
-	int			index = 0;
-	int			partial_copy = 0;
-	int			partial_copy_len = 0;
 	int			contwr = 0;
 	int			record_cnt = 0;
 	int			data_cnt = 0;
 	int			error = 0;
+	int			log_offset;
 
 	if (ticket->t_curr_res < 0) {
 		xfs_alert_tag(log->l_mp, XFS_PTAG_LOGRES,
@@ -2328,157 +2409,52 @@  xlog_write(
 		xfs_force_shutdown(log->l_mp, SHUTDOWN_LOG_IO_ERROR);
 	}
 
-	if (start_lsn)
-		*start_lsn = 0;
-	while (lv && (!lv->lv_niovecs || index < lv->lv_niovecs)) {
-		void		*ptr;
-		int		log_offset;
-
-		error = xlog_state_get_iclog_space(log, len, &iclog, ticket,
-						   &contwr, &log_offset);
-		if (error)
-			return error;
-
-		ASSERT(log_offset <= iclog->ic_size - 1);
+	error = xlog_state_get_iclog_space(log, len, &iclog, ticket,
+					   &contwr, &log_offset);
+	if (error)
+		return error;
 
-		/* Start_lsn is the first lsn written to. */
-		if (start_lsn && !*start_lsn)
-			*start_lsn = be64_to_cpu(iclog->ic_header.h_lsn);
+	/* start_lsn is the LSN of the first iclog written to. */
+	if (start_lsn)
+		*start_lsn = be64_to_cpu(iclog->ic_header.h_lsn);
 
-		/*
-		 * iclogs containing commit records or unmount records need
-		 * to issue ordering cache flushes and commit immediately
-		 * to stable storage to guarantee journal vs metadata ordering
-		 * is correctly maintained in the storage media.
-		 */
-		if (optype & (XLOG_COMMIT_TRANS | XLOG_UNMOUNT_TRANS)) {
-			iclog->ic_flags |= (XLOG_ICL_NEED_FLUSH |
-						XLOG_ICL_NEED_FUA);
-		}
+	/*
+	 * iclogs containing commit records or unmount records need
+	 * to issue ordering cache flushes and commit immediately
+	 * to stable storage to guarantee journal vs metadata ordering
+	 * is correctly maintained in the storage media. This will always
+	 * fit in the iclog we have been already been passed.
+	 */
+	if (optype & (XLOG_COMMIT_TRANS | XLOG_UNMOUNT_TRANS)) {
+		iclog->ic_flags |= (XLOG_ICL_NEED_FLUSH | XLOG_ICL_NEED_FUA);
+		ASSERT(!contwr);
+	}
 
-		/* If this is a single iclog write, go fast... */
-		if (!contwr && lv == log_vector) {
-			record_cnt = xlog_write_single(lv, ticket, iclog,
-						log_offset, len);
-			len = 0;
-			data_cnt = len;
+	while (lv) {
+		lv = xlog_write_single(lv, ticket, iclog, &log_offset,
+					&len, &record_cnt, &data_cnt);
+		if (!lv)
 			break;
-		}
-
-		/*
-		 * This loop writes out as many regions as can fit in the amount
-		 * of space which was allocated by xlog_state_get_iclog_space().
-		 */
-		ptr = iclog->ic_datap + log_offset;
-		while (lv && (!lv->lv_niovecs || index < lv->lv_niovecs)) {
-			struct xfs_log_iovec	*reg;
-			struct xlog_op_header	*ophdr;
-			int			copy_len;
-			int			copy_off;
-			bool			ordered = false;
-			bool			added_ophdr = false;
-
-			/* ordered log vectors have no regions to write */
-			if (lv->lv_buf_len == XFS_LOG_VEC_ORDERED) {
-				ASSERT(lv->lv_niovecs == 0);
-				ordered = true;
-				goto next_lv;
-			}
-
-			reg = &vecp[index];
-			ASSERT(reg->i_len % sizeof(int32_t) == 0);
-			ASSERT((unsigned long)ptr % sizeof(int32_t) == 0);
-
-			/*
-			 * Regions always have their ophdr at the start of the
-			 * region, except for:
-			 * - a transaction start which has a start record ophdr
-			 *   before the first region ophdr; and
-			 * - the previous region didn't fully fit into an iclog
-			 *   so needs a continuation ophdr to prepend the region
-			 *   in this new iclog.
-			 */
-			ophdr = reg->i_addr;
-			if (optype && index) {
-				optype &= ~XLOG_START_TRANS;
-			} else if (partial_copy) {
-                                ophdr = xlog_write_setup_ophdr(ptr, ticket);
-				xlog_write_adv_cnt(&ptr, &len, &log_offset,
-					   sizeof(struct xlog_op_header));
-				added_ophdr = true;
-			}
-			ophdr->oh_tid = cpu_to_be32(ticket->t_tid);
-
-			len += xlog_write_setup_copy(ticket, ophdr,
-						     iclog->ic_size-log_offset,
-						     reg->i_len,
-						     &copy_off, &copy_len,
-						     &partial_copy,
-						     &partial_copy_len);
-			xlog_verify_dest_ptr(log, ptr);
-
 
-			/*
-			 * Wart: need to update length in embedded ophdr not
-			 * to include it's own length.
-			 */
-			if (!added_ophdr) {
-				ophdr->oh_len = cpu_to_be32(copy_len -
-						sizeof(struct xlog_op_header));
-			}
-
-			ASSERT(copy_len > 0);
-			memcpy(ptr, reg->i_addr + copy_off, copy_len);
-			xlog_write_adv_cnt(&ptr, &len, &log_offset, copy_len);
-
-			if (added_ophdr)
-				copy_len += sizeof(struct xlog_op_header);
-			record_cnt++;
-			data_cnt += contwr ? copy_len : 0;
-
-			error = xlog_write_copy_finish(log, iclog, optype,
-						       &record_cnt, &data_cnt,
-						       &partial_copy,
-						       &partial_copy_len,
-						       log_offset,
-						       commit_iclog);
-			if (error)
-				return error;
-
-			/*
-			 * if we had a partial copy, we need to get more iclog
-			 * space but we don't want to increment the region
-			 * index because there is still more is this region to
-			 * write.
-			 *
-			 * If we completed writing this region, and we flushed
-			 * the iclog (indicated by resetting of the record
-			 * count), then we also need to get more log space. If
-			 * this was the last record, though, we are done and
-			 * can just return.
-			 */
-			if (partial_copy)
-				break;
-
-			if (++index == lv->lv_niovecs) {
-next_lv:
-				lv = lv->lv_next;
-				index = 0;
-				if (lv)
-					vecp = lv->lv_iovecp;
-			}
-			if (record_cnt == 0 && !ordered) {
-				if (!lv)
-					return 0;
-				break;
-			}
+		ASSERT(!(optype & (XLOG_COMMIT_TRANS | XLOG_UNMOUNT_TRANS)));
+		lv = xlog_write_partial(log, lv, ticket, &iclog, &log_offset,
+					&len, &record_cnt, &data_cnt, &contwr);
+		if (IS_ERR_OR_NULL(lv)) {
+			error = PTR_ERR_OR_ZERO(lv);
+			break;
 		}
 	}
+	ASSERT((len == 0 && !lv) || error);
 
-	ASSERT(len == 0);
-
+	/*
+	 * We've already been guaranteed that the last writes will fit inside
+	 * the current iclog, and hence it will already have the space used by
+	 * those writes accounted to it. Hence we do not need to update the
+	 * iclog with the number of bytes written here.
+	 */
+	ASSERT(!contwr || XLOG_FORCED_SHUTDOWN(log));
 	spin_lock(&log->l_icloglock);
-	xlog_state_finish_copy(log, iclog, record_cnt, data_cnt);
+	xlog_state_finish_copy(log, iclog, record_cnt, 0);
 	if (commit_iclog) {
 		ASSERT(optype & XLOG_COMMIT_TRANS);
 		*commit_iclog = iclog;
@@ -2930,7 +2906,7 @@  xlog_state_get_iclog_space(
 	 * xlog_write() algorithm assumes that at least 2 xlog_op_header_t's
 	 * can fit into remaining data section.
 	 */
-	if (iclog->ic_size - iclog->ic_offset < 2*sizeof(xlog_op_header_t)) {
+	if (iclog->ic_size - iclog->ic_offset < 3*sizeof(xlog_op_header_t)) {
 		int		error = 0;
 
 		xlog_state_switch_iclogs(log, iclog, iclog->ic_size);
@@ -3633,11 +3609,12 @@  xlog_verify_iclog(
 					iclog->ic_header.h_cycle_data[idx]);
 			}
 		}
-		if (clientid != XFS_TRANSACTION && clientid != XFS_LOG)
+		if (clientid != XFS_TRANSACTION && clientid != XFS_LOG) {
 			xfs_warn(log->l_mp,
-				"%s: invalid clientid %d op "PTR_FMT" offset 0x%lx",
-				__func__, clientid, ophead,
+				"%s: op %d invalid clientid %d op "PTR_FMT" offset 0x%lx",
+				__func__, i, clientid, ophead,
 				(unsigned long)field_offset);
+		}
 
 		/* check length */
 		p = &ophead->oh_len;