diff mbox

[11/47] xfs: move deferred operations into a separate file

Message ID 146907703710.25461.16650495404061662831.stgit@birch.djwong.org
State Accepted
Headers show

Commit Message

Darrick J. Wong July 21, 2016, 4:57 a.m. UTC
All the code around struct xfs_bmap_free basically implements a
deferred operation framework through which we can roll transactions
(to unlock buffers and avoid violating lock order rules) while
managing all the necessary log redo items.  Previously we only used
this code to free extents after some sort of mapping operation, but
with the advent of rmap and reflink, we suddenly need to do more than
that.

With that in mind, xfs_bmap_free really becomes a deferred ops control
structure.  Rename the structure and move the deferred ops into their
own file to avoid further bloating of the bmap code.

v2: actually sort the work items by AG to avoid deadlocks.

v3: split out the -EAGAIN continuation handling into a separate patch.

Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
---
 fs/xfs/Makefile           |    1 
 fs/xfs/libxfs/xfs_defer.c |  444 +++++++++++++++++++++++++++++++++++++++++++++
 fs/xfs/libxfs/xfs_defer.h |   95 ++++++++++
 3 files changed, 540 insertions(+)
 create mode 100644 fs/xfs/libxfs/xfs_defer.c
 create mode 100644 fs/xfs/libxfs/xfs_defer.h

Comments

Christoph Hellwig Aug. 1, 2016, 7:08 a.m. UTC | #1
> + * NOTE: To avoid exceeding the transaction reservation, we limit the
> + * number of items that we attach to a given xfs_defer_pending.

This seems like a new feature compared to the old bmap_free code,
can you explain it it in a little more detail?  As I'm trying to compare
this code to the existing one there are a few things that confuse me,
most importantly the purpose of the xfs_defer_pending structure,
which seems like a new indirection.  I don't really like that
indirection at all, as it introduces another memory allocation deep
down in the commit path where we can't recover from ENOMEM.  Also there
seems to be a 1:1 relationship between it and the xfs_bmap_free_item
structure that got renamed to xfs_extent_free_item.

> +static const struct xfs_defer_op_type *defer_op_types[XFS_DEFER_OPS_TYPE_MAX];

We shouldn't really need this global array and the xfs_defer_ops_type
enum, just pass the xfs_defer_op_type pointer into xfs_defer_add.
Christoph Hellwig Aug. 1, 2016, 8:02 a.m. UTC | #2
I looked over this again and I really don't see the use case of merging
it.  Yes, the freed extent, rmap and reflink code is fairly similar, but
there is all kinds of subtile differences that we need to paper over using
methods and flags.  I think we're better off not trying to share this
code and have a separate, but easily understandable implementation
for each btree.  At least for the traditional traditional freed extent
case the new code also is a lot less optimal than the previous version.
Brian Foster Aug. 2, 2016, 5:30 p.m. UTC | #3
On Wed, Jul 20, 2016 at 09:57:17PM -0700, Darrick J. Wong wrote:
> All the code around struct xfs_bmap_free basically implements a
> deferred operation framework through which we can roll transactions
> (to unlock buffers and avoid violating lock order rules) while
> managing all the necessary log redo items.  Previously we only used
> this code to free extents after some sort of mapping operation, but
> with the advent of rmap and reflink, we suddenly need to do more than
> that.
> 
> With that in mind, xfs_bmap_free really becomes a deferred ops control
> structure.  Rename the structure and move the deferred ops into their
> own file to avoid further bloating of the bmap code.
> 
> v2: actually sort the work items by AG to avoid deadlocks.
> 
> v3: split out the -EAGAIN continuation handling into a separate patch.
> 
> Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
> ---

Fixes up my comments from the previous version and punts off the EAGAIN
stuff. hch's comments aside, this looks Ok to me:

Reviewed-by: Brian Foster <bfoster@redhat.com>

>  fs/xfs/Makefile           |    1 
>  fs/xfs/libxfs/xfs_defer.c |  444 +++++++++++++++++++++++++++++++++++++++++++++
>  fs/xfs/libxfs/xfs_defer.h |   95 ++++++++++
>  3 files changed, 540 insertions(+)
>  create mode 100644 fs/xfs/libxfs/xfs_defer.c
>  create mode 100644 fs/xfs/libxfs/xfs_defer.h
> 
> 
> diff --git a/fs/xfs/Makefile b/fs/xfs/Makefile
> index 3542d94..01857b0 100644
> --- a/fs/xfs/Makefile
> +++ b/fs/xfs/Makefile
> @@ -39,6 +39,7 @@ xfs-y				+= $(addprefix libxfs/, \
>  				   xfs_btree.o \
>  				   xfs_da_btree.o \
>  				   xfs_da_format.o \
> +				   xfs_defer.o \
>  				   xfs_dir2.o \
>  				   xfs_dir2_block.o \
>  				   xfs_dir2_data.o \
> diff --git a/fs/xfs/libxfs/xfs_defer.c b/fs/xfs/libxfs/xfs_defer.c
> new file mode 100644
> index 0000000..2809db7
> --- /dev/null
> +++ b/fs/xfs/libxfs/xfs_defer.c
> @@ -0,0 +1,444 @@
> +/*
> + * Copyright (C) 2016 Oracle.  All Rights Reserved.
> + *
> + * Author: Darrick J. Wong <darrick.wong@oracle.com>
> + *
> + * This program is free software; you can redistribute it and/or
> + * modify it under the terms of the GNU General Public License
> + * as published by the Free Software Foundation; either version 2
> + * of the License, or (at your option) any later version.
> + *
> + * This program is distributed in the hope that it would be useful,
> + * but WITHOUT ANY WARRANTY; without even the implied warranty of
> + * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
> + * GNU General Public License for more details.
> + *
> + * You should have received a copy of the GNU General Public License
> + * along with this program; if not, write the Free Software Foundation,
> + * Inc.,  51 Franklin St, Fifth Floor, Boston, MA  02110-1301, USA.
> + */
> +#include "xfs.h"
> +#include "xfs_fs.h"
> +#include "xfs_shared.h"
> +#include "xfs_format.h"
> +#include "xfs_log_format.h"
> +#include "xfs_trans_resv.h"
> +#include "xfs_bit.h"
> +#include "xfs_sb.h"
> +#include "xfs_mount.h"
> +#include "xfs_defer.h"
> +#include "xfs_trans.h"
> +#include "xfs_trace.h"
> +
> +/*
> + * Deferred Operations in XFS
> + *
> + * Due to the way locking rules work in XFS, certain transactions (block
> + * mapping and unmapping, typically) have permanent reservations so that
> + * we can roll the transaction to adhere to AG locking order rules and
> + * to unlock buffers between metadata updates.  Prior to rmap/reflink,
> + * the mapping code had a mechanism to perform these deferrals for
> + * extents that were going to be freed; this code makes that facility
> + * more generic.
> + *
> + * When adding the reverse mapping and reflink features, it became
> + * necessary to perform complex remapping multi-transactions to comply
> + * with AG locking order rules, and to be able to spread a single
> + * refcount update operation (an operation on an n-block extent can
> + * update as many as n records!) among multiple transactions.  XFS can
> + * roll a transaction to facilitate this, but using this facility
> + * requires us to log "intent" items in case log recovery needs to
> + * redo the operation, and to log "done" items to indicate that redo
> + * is not necessary.
> + *
> + * Deferred work is tracked in xfs_defer_pending items.  Each pending
> + * item tracks one type of deferred work.  Incoming work items (which
> + * have not yet had an intent logged) are attached to a pending item
> + * on the dop_intake list, where they wait for the caller to finish
> + * the deferred operations.
> + *
> + * Finishing a set of deferred operations is an involved process.  To
> + * start, we define "rolling a deferred-op transaction" as follows:
> + *
> + * > For each xfs_defer_pending item on the dop_intake list,
> + *   - Sort the work items in AG order.  XFS locking
> + *     order rules require us to lock buffers in AG order.
> + *   - Create a log intent item for that type.
> + *   - Attach it to the pending item.
> + *   - Move the pending item from the dop_intake list to the
> + *     dop_pending list.
> + * > Roll the transaction.
> + *
> + * NOTE: To avoid exceeding the transaction reservation, we limit the
> + * number of items that we attach to a given xfs_defer_pending.
> + *
> + * The actual finishing process looks like this:
> + *
> + * > For each xfs_defer_pending in the dop_pending list,
> + *   - Roll the deferred-op transaction as above.
> + *   - Create a log done item for that type, and attach it to the
> + *     log intent item.
> + *   - For each work item attached to the log intent item,
> + *     * Perform the described action.
> + *     * Attach the work item to the log done item.
> + *
> + * The key here is that we must log an intent item for all pending
> + * work items every time we roll the transaction, and that we must log
> + * a done item as soon as the work is completed.  With this mechanism
> + * we can perform complex remapping operations, chaining intent items
> + * as needed.
> + *
> + * This is an example of remapping the extent (E, E+B) into file X at
> + * offset A and dealing with the extent (C, C+B) already being mapped
> + * there:
> + * +-------------------------------------------------+
> + * | Unmap file X startblock C offset A length B     | t0
> + * | Intent to reduce refcount for extent (C, B)     |
> + * | Intent to remove rmap (X, C, A, B)              |
> + * | Intent to free extent (D, 1) (bmbt block)       |
> + * | Intent to map (X, A, B) at startblock E         |
> + * +-------------------------------------------------+
> + * | Map file X startblock E offset A length B       | t1
> + * | Done mapping (X, E, A, B)                       |
> + * | Intent to increase refcount for extent (E, B)   |
> + * | Intent to add rmap (X, E, A, B)                 |
> + * +-------------------------------------------------+
> + * | Reduce refcount for extent (C, B)               | t2
> + * | Done reducing refcount for extent (C, B)        |
> + * | Increase refcount for extent (E, B)             |
> + * | Done increasing refcount for extent (E, B)      |
> + * | Intent to free extent (C, B)                    |
> + * | Intent to free extent (F, 1) (refcountbt block) |
> + * | Intent to remove rmap (F, 1, REFC)              |
> + * +-------------------------------------------------+
> + * | Remove rmap (X, C, A, B)                        | t3
> + * | Done removing rmap (X, C, A, B)                 |
> + * | Add rmap (X, E, A, B)                           |
> + * | Done adding rmap (X, E, A, B)                   |
> + * | Remove rmap (F, 1, REFC)                        |
> + * | Done removing rmap (F, 1, REFC)                 |
> + * +-------------------------------------------------+
> + * | Free extent (C, B)                              | t4
> + * | Done freeing extent (C, B)                      |
> + * | Free extent (D, 1)                              |
> + * | Done freeing extent (D, 1)                      |
> + * | Free extent (F, 1)                              |
> + * | Done freeing extent (F, 1)                      |
> + * +-------------------------------------------------+
> + *
> + * If we should crash before t2 commits, log recovery replays
> + * the following intent items:
> + *
> + * - Intent to reduce refcount for extent (C, B)
> + * - Intent to remove rmap (X, C, A, B)
> + * - Intent to free extent (D, 1) (bmbt block)
> + * - Intent to increase refcount for extent (E, B)
> + * - Intent to add rmap (X, E, A, B)
> + *
> + * In the process of recovering, it should also generate and take care
> + * of these intent items:
> + *
> + * - Intent to free extent (C, B)
> + * - Intent to free extent (F, 1) (refcountbt block)
> + * - Intent to remove rmap (F, 1, REFC)
> + */
> +
> +static const struct xfs_defer_op_type *defer_op_types[XFS_DEFER_OPS_TYPE_MAX];
> +
> +/*
> + * For each pending item in the intake list, log its intent item and the
> + * associated extents, then add the entire intake list to the end of
> + * the pending list.
> + */
> +STATIC void
> +xfs_defer_intake_work(
> +	struct xfs_trans		*tp,
> +	struct xfs_defer_ops		*dop)
> +{
> +	struct list_head		*li;
> +	struct xfs_defer_pending	*dfp;
> +
> +	list_for_each_entry(dfp, &dop->dop_intake, dfp_list) {
> +		dfp->dfp_intent = dfp->dfp_type->create_intent(tp,
> +				dfp->dfp_count);
> +		list_sort(tp->t_mountp, &dfp->dfp_work,
> +				dfp->dfp_type->diff_items);
> +		list_for_each(li, &dfp->dfp_work)
> +			dfp->dfp_type->log_item(tp, dfp->dfp_intent, li);
> +	}
> +
> +	list_splice_tail_init(&dop->dop_intake, &dop->dop_pending);
> +}
> +
> +/* Abort all the intents that were committed. */
> +STATIC void
> +xfs_defer_trans_abort(
> +	struct xfs_trans		*tp,
> +	struct xfs_defer_ops		*dop,
> +	int				error)
> +{
> +	struct xfs_defer_pending	*dfp;
> +
> +	/*
> +	 * If the transaction was committed, drop the intent reference
> +	 * since we're bailing out of here. The other reference is
> +	 * dropped when the intent hits the AIL.  If the transaction
> +	 * was not committed, the intent is freed by the intent item
> +	 * unlock handler on abort.
> +	 */
> +	if (!dop->dop_committed)
> +		return;
> +
> +	/* Abort intent items. */
> +	list_for_each_entry(dfp, &dop->dop_pending, dfp_list) {
> +		if (dfp->dfp_committed)
> +			dfp->dfp_type->abort_intent(dfp->dfp_intent);
> +	}
> +
> +	/* Shut down FS. */
> +	xfs_force_shutdown(tp->t_mountp, (error == -EFSCORRUPTED) ?
> +			SHUTDOWN_CORRUPT_INCORE : SHUTDOWN_META_IO_ERROR);
> +}
> +
> +/* Roll a transaction so we can do some deferred op processing. */
> +STATIC int
> +xfs_defer_trans_roll(
> +	struct xfs_trans		**tp,
> +	struct xfs_defer_ops		*dop,
> +	struct xfs_inode		*ip)
> +{
> +	int				i;
> +	int				error;
> +
> +	/* Log all the joined inodes except the one we passed in. */
> +	for (i = 0; i < XFS_DEFER_OPS_NR_INODES && dop->dop_inodes[i]; i++) {
> +		if (dop->dop_inodes[i] == ip)
> +			continue;
> +		xfs_trans_log_inode(*tp, dop->dop_inodes[i], XFS_ILOG_CORE);
> +	}
> +
> +	/* Roll the transaction. */
> +	error = xfs_trans_roll(tp, ip);
> +	if (error) {
> +		xfs_defer_trans_abort(*tp, dop, error);
> +		return error;
> +	}
> +	dop->dop_committed = true;
> +
> +	/* Rejoin the joined inodes except the one we passed in. */
> +	for (i = 0; i < XFS_DEFER_OPS_NR_INODES && dop->dop_inodes[i]; i++) {
> +		if (dop->dop_inodes[i] == ip)
> +			continue;
> +		xfs_trans_ijoin(*tp, dop->dop_inodes[i], 0);
> +	}
> +
> +	return error;
> +}
> +
> +/* Do we have any work items to finish? */
> +bool
> +xfs_defer_has_unfinished_work(
> +	struct xfs_defer_ops		*dop)
> +{
> +	return !list_empty(&dop->dop_pending) || !list_empty(&dop->dop_intake);
> +}
> +
> +/*
> + * Add this inode to the deferred op.  Each joined inode is relogged
> + * each time we roll the transaction, in addition to any inode passed
> + * to xfs_defer_finish().
> + */
> +int
> +xfs_defer_join(
> +	struct xfs_defer_ops		*dop,
> +	struct xfs_inode		*ip)
> +{
> +	int				i;
> +
> +	for (i = 0; i < XFS_DEFER_OPS_NR_INODES; i++) {
> +		if (dop->dop_inodes[i] == ip)
> +			return 0;
> +		else if (dop->dop_inodes[i] == NULL) {
> +			dop->dop_inodes[i] = ip;
> +			return 0;
> +		}
> +	}
> +
> +	return -EFSCORRUPTED;
> +}
> +
> +/*
> + * Finish all the pending work.  This involves logging intent items for
> + * any work items that wandered in since the last transaction roll (if
> + * one has even happened), rolling the transaction, and finishing the
> + * work items in the first item on the logged-and-pending list.
> + *
> + * If an inode is provided, relog it to the new transaction.
> + */
> +int
> +xfs_defer_finish(
> +	struct xfs_trans		**tp,
> +	struct xfs_defer_ops		*dop,
> +	struct xfs_inode		*ip)
> +{
> +	struct xfs_defer_pending	*dfp;
> +	struct list_head		*li;
> +	struct list_head		*n;
> +	void				*done_item = NULL;
> +	void				*state;
> +	int				error = 0;
> +	void				(*cleanup_fn)(struct xfs_trans *, void *, int);
> +
> +	ASSERT((*tp)->t_flags & XFS_TRANS_PERM_LOG_RES);
> +
> +	/* Until we run out of pending work to finish... */
> +	while (xfs_defer_has_unfinished_work(dop)) {
> +		/* Log intents for work items sitting in the intake. */
> +		xfs_defer_intake_work(*tp, dop);
> +
> +		/* Roll the transaction. */
> +		error = xfs_defer_trans_roll(tp, dop, ip);
> +		if (error)
> +			goto out;
> +
> +		/* Mark all pending intents as committed. */
> +		list_for_each_entry_reverse(dfp, &dop->dop_pending, dfp_list) {
> +			if (dfp->dfp_committed)
> +				break;
> +			dfp->dfp_committed = true;
> +		}
> +
> +		/* Log an intent-done item for the first pending item. */
> +		dfp = list_first_entry(&dop->dop_pending,
> +				struct xfs_defer_pending, dfp_list);
> +		done_item = dfp->dfp_type->create_done(*tp, dfp->dfp_intent,
> +				dfp->dfp_count);
> +		cleanup_fn = dfp->dfp_type->finish_cleanup;
> +
> +		/* Finish the work items. */
> +		state = NULL;
> +		list_for_each_safe(li, n, &dfp->dfp_work) {
> +			list_del(li);
> +			dfp->dfp_count--;
> +			error = dfp->dfp_type->finish_item(*tp, dop, li,
> +					done_item, &state);
> +			if (error) {
> +				/*
> +				 * Clean up after ourselves and jump out.
> +				 * xfs_defer_cancel will take care of freeing
> +				 * all these lists and stuff.
> +				 */
> +				if (cleanup_fn)
> +					cleanup_fn(*tp, state, error);
> +				xfs_defer_trans_abort(*tp, dop, error);
> +				goto out;
> +			}
> +		}
> +		/* Done with the dfp, free it. */
> +		list_del(&dfp->dfp_list);
> +		kmem_free(dfp);
> +
> +		if (cleanup_fn)
> +			cleanup_fn(*tp, state, error);
> +	}
> +
> +out:
> +	return error;
> +}
> +
> +/*
> + * Free up any items left in the list.
> + */
> +void
> +xfs_defer_cancel(
> +	struct xfs_defer_ops		*dop)
> +{
> +	struct xfs_defer_pending	*dfp;
> +	struct xfs_defer_pending	*pli;
> +	struct list_head		*pwi;
> +	struct list_head		*n;
> +
> +	/*
> +	 * Free the pending items.  Caller should already have arranged
> +	 * for the intent items to be released.
> +	 */
> +	list_for_each_entry_safe(dfp, pli, &dop->dop_intake, dfp_list) {
> +		list_del(&dfp->dfp_list);
> +		list_for_each_safe(pwi, n, &dfp->dfp_work) {
> +			list_del(pwi);
> +			dfp->dfp_count--;
> +			dfp->dfp_type->cancel_item(pwi);
> +		}
> +		ASSERT(dfp->dfp_count == 0);
> +		kmem_free(dfp);
> +	}
> +	list_for_each_entry_safe(dfp, pli, &dop->dop_pending, dfp_list) {
> +		list_del(&dfp->dfp_list);
> +		list_for_each_safe(pwi, n, &dfp->dfp_work) {
> +			list_del(pwi);
> +			dfp->dfp_count--;
> +			dfp->dfp_type->cancel_item(pwi);
> +		}
> +		ASSERT(dfp->dfp_count == 0);
> +		kmem_free(dfp);
> +	}
> +}
> +
> +/* Add an item for later deferred processing. */
> +void
> +xfs_defer_add(
> +	struct xfs_defer_ops		*dop,
> +	enum xfs_defer_ops_type		type,
> +	struct list_head		*li)
> +{
> +	struct xfs_defer_pending	*dfp = NULL;
> +
> +	/*
> +	 * Add the item to a pending item at the end of the intake list.
> +	 * If the last pending item has the same type, reuse it.  Else,
> +	 * create a new pending item at the end of the intake list.
> +	 */
> +	if (!list_empty(&dop->dop_intake)) {
> +		dfp = list_last_entry(&dop->dop_intake,
> +				struct xfs_defer_pending, dfp_list);
> +		if (dfp->dfp_type->type != type ||
> +		    (dfp->dfp_type->max_items &&
> +		     dfp->dfp_count >= dfp->dfp_type->max_items))
> +			dfp = NULL;
> +	}
> +	if (!dfp) {
> +		dfp = kmem_alloc(sizeof(struct xfs_defer_pending),
> +				KM_SLEEP | KM_NOFS);
> +		dfp->dfp_type = defer_op_types[type];
> +		dfp->dfp_committed = false;
> +		dfp->dfp_intent = NULL;
> +		dfp->dfp_count = 0;
> +		INIT_LIST_HEAD(&dfp->dfp_work);
> +		list_add_tail(&dfp->dfp_list, &dop->dop_intake);
> +	}
> +
> +	list_add_tail(li, &dfp->dfp_work);
> +	dfp->dfp_count++;
> +}
> +
> +/* Initialize a deferred operation list. */
> +void
> +xfs_defer_init_op_type(
> +	const struct xfs_defer_op_type	*type)
> +{
> +	defer_op_types[type->type] = type;
> +}
> +
> +/* Initialize a deferred operation. */
> +void
> +xfs_defer_init(
> +	struct xfs_defer_ops		*dop,
> +	xfs_fsblock_t			*fbp)
> +{
> +	dop->dop_committed = false;
> +	dop->dop_low = false;
> +	memset(&dop->dop_inodes, 0, sizeof(dop->dop_inodes));
> +	*fbp = NULLFSBLOCK;
> +	INIT_LIST_HEAD(&dop->dop_intake);
> +	INIT_LIST_HEAD(&dop->dop_pending);
> +}
> diff --git a/fs/xfs/libxfs/xfs_defer.h b/fs/xfs/libxfs/xfs_defer.h
> new file mode 100644
> index 0000000..a227bd2
> --- /dev/null
> +++ b/fs/xfs/libxfs/xfs_defer.h
> @@ -0,0 +1,95 @@
> +/*
> + * Copyright (C) 2016 Oracle.  All Rights Reserved.
> + *
> + * Author: Darrick J. Wong <darrick.wong@oracle.com>
> + *
> + * This program is free software; you can redistribute it and/or
> + * modify it under the terms of the GNU General Public License
> + * as published by the Free Software Foundation; either version 2
> + * of the License, or (at your option) any later version.
> + *
> + * This program is distributed in the hope that it would be useful,
> + * but WITHOUT ANY WARRANTY; without even the implied warranty of
> + * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
> + * GNU General Public License for more details.
> + *
> + * You should have received a copy of the GNU General Public License
> + * along with this program; if not, write the Free Software Foundation,
> + * Inc.,  51 Franklin St, Fifth Floor, Boston, MA  02110-1301, USA.
> + */
> +#ifndef __XFS_DEFER_H__
> +#define	__XFS_DEFER_H__
> +
> +struct xfs_defer_op_type;
> +
> +/*
> + * Save a log intent item and a list of extents, so that we can replay
> + * whatever action had to happen to the extent list and file the log done
> + * item.
> + */
> +struct xfs_defer_pending {
> +	const struct xfs_defer_op_type	*dfp_type;	/* function pointers */
> +	struct list_head		dfp_list;	/* pending items */
> +	bool				dfp_committed;	/* committed trans? */
> +	void				*dfp_intent;	/* log intent item */
> +	struct list_head		dfp_work;	/* work items */
> +	unsigned int			dfp_count;	/* # extent items */
> +};
> +
> +/*
> + * Header for deferred operation list.
> + *
> + * dop_low is used by the allocator to activate the lowspace algorithm -
> + * when free space is running low the extent allocator may choose to
> + * allocate an extent from an AG without leaving sufficient space for
> + * a btree split when inserting the new extent.  In this case the allocator
> + * will enable the lowspace algorithm which is supposed to allow further
> + * allocations (such as btree splits and newroots) to allocate from
> + * sequential AGs.  In order to avoid locking AGs out of order the lowspace
> + * algorithm will start searching for free space from AG 0.  If the correct
> + * transaction reservations have been made then this algorithm will eventually
> + * find all the space it needs.
> + */
> +enum xfs_defer_ops_type {
> +	XFS_DEFER_OPS_TYPE_MAX,
> +};
> +
> +#define XFS_DEFER_OPS_NR_INODES	2	/* join up to two inodes */
> +
> +struct xfs_defer_ops {
> +	bool			dop_committed;	/* did any trans commit? */
> +	bool			dop_low;	/* alloc in low mode */
> +	struct list_head	dop_intake;	/* unlogged pending work */
> +	struct list_head	dop_pending;	/* logged pending work */
> +
> +	/* relog these inodes with each roll */
> +	struct xfs_inode	*dop_inodes[XFS_DEFER_OPS_NR_INODES];
> +};
> +
> +void xfs_defer_add(struct xfs_defer_ops *dop, enum xfs_defer_ops_type type,
> +		struct list_head *h);
> +int xfs_defer_finish(struct xfs_trans **tp, struct xfs_defer_ops *dop,
> +		struct xfs_inode *ip);
> +void xfs_defer_cancel(struct xfs_defer_ops *dop);
> +void xfs_defer_init(struct xfs_defer_ops *dop, xfs_fsblock_t *fbp);
> +bool xfs_defer_has_unfinished_work(struct xfs_defer_ops *dop);
> +int xfs_defer_join(struct xfs_defer_ops *dop, struct xfs_inode *ip);
> +
> +/* Description of a deferred type. */
> +struct xfs_defer_op_type {
> +	enum xfs_defer_ops_type	type;
> +	unsigned int		max_items;
> +	void (*abort_intent)(void *);
> +	void *(*create_done)(struct xfs_trans *, void *, unsigned int);
> +	int (*finish_item)(struct xfs_trans *, struct xfs_defer_ops *,
> +			struct list_head *, void *, void **);
> +	void (*finish_cleanup)(struct xfs_trans *, void *, int);
> +	void (*cancel_item)(struct list_head *);
> +	int (*diff_items)(void *, struct list_head *, struct list_head *);
> +	void *(*create_intent)(struct xfs_trans *, uint);
> +	void (*log_item)(struct xfs_trans *, void *, struct list_head *);
> +};
> +
> +void xfs_defer_init_op_type(const struct xfs_defer_op_type *type);
> +
> +#endif /* __XFS_DEFER_H__ */
> 
> _______________________________________________
> xfs mailing list
> xfs@oss.sgi.com
> http://oss.sgi.com/mailman/listinfo/xfs
Dave Chinner Aug. 2, 2016, 10:39 p.m. UTC | #4
On Mon, Aug 01, 2016 at 01:02:23AM -0700, Christoph Hellwig wrote:
> I looked over this again and I really don't see the use case of merging
> it.  Yes, the freed extent, rmap and reflink code is fairly similar, but
> there is all kinds of subtile differences that we need to paper over using
> methods and flags.  I think we're better off not trying to share this
> code and have a separate, but easily understandable implementation
> for each btree.  At least for the traditional traditional freed extent
> case the new code also is a lot less optimal than the previous version.

Rather than have to make major changes to core infrastructure now,
let's work this out as a separate patchset to clean up the rmap and
reflink code in the next couple of releases. It's going to be better
to get working code out there now under the experimental tag than it
is is to keep it as an out of tree patchset for another cycle.

Cheers,

Dave.
Christoph Hellwig Aug. 3, 2016, 9:16 a.m. UTC | #5
On Wed, Aug 03, 2016 at 08:39:50AM +1000, Dave Chinner wrote:
> Rather than have to make major changes to core infrastructure now,
> let's work this out as a separate patchset to clean up the rmap and
> reflink code in the next couple of releases. It's going to be better
> to get working code out there now under the experimental tag than it
> is is to keep it as an out of tree patchset for another cycle.

The problm is that this does not only affect the rmap code (for which
I suspect it actually is fine), but also regresses the freed extent
logging.  If you want minimal changes we should simply drop the patches
to move over the freed extent tracking to the new deferred ops
mechanism for now.
Dave Chinner Aug. 3, 2016, 10:57 p.m. UTC | #6
On Wed, Aug 03, 2016 at 02:16:27AM -0700, Christoph Hellwig wrote:
> On Wed, Aug 03, 2016 at 08:39:50AM +1000, Dave Chinner wrote:
> > Rather than have to make major changes to core infrastructure now,
> > let's work this out as a separate patchset to clean up the rmap and
> > reflink code in the next couple of releases. It's going to be better
> > to get working code out there now under the experimental tag than it
> > is is to keep it as an out of tree patchset for another cycle.
> 
> The problm is that this does not only affect the rmap code (for which
> I suspect it actually is fine), but also regresses the freed extent
> logging.  If you want minimal changes we should simply drop the patches
> to move over the freed extent tracking to the new deferred ops
> mechanism for now.

I haven't said I want "minimal changes". 

What I don't want to do is make large, untested changes at the last
minute, especially when there's no evidence that there is a
regression caused by the code being changed. We need this kind of
infrastructure for reflink, and there's no point rewriting the rmap
code to remove it just to then have to immediately re-introduce it
back into to the rmap code so it works with reflink. It's pointless
churn and invalidates all the testing we've done on rmap up to this
point.

I don't understand what problem or regression you think this code
causes, mainly because it hasn't been explained or demonstrated. I
don't understand the solution being proposed, because the little
that has been described tells me nothing about what the problem it
solves is, nor how it solves the atomicity and ordering requirements
that updating the bmbt, refcountbt and rmapbt have.

I have no issues with fixing the code if it is broken, but first
everyone needs to undestand how it is broken. It's time to make
progress on this functionality - if we wait for the code to be
perfect before it gets merged, we'll never make any progress.

So, please explain in more detail what the problem is and what the
proposed solution is so I (and probably Darrick, too) have some
understanding of the issue you see with this code.

Cheers,

Dave.
Christoph Hellwig Aug. 4, 2016, 4 p.m. UTC | #7
On Thu, Aug 04, 2016 at 08:57:56AM +1000, Dave Chinner wrote:
> So, please explain in more detail what the problem is and what the
> proposed solution is so I (and probably Darrick, too) have some
> understanding of the issue you see with this code.

We were doing 1 (actually 2 with the busy extent tracking) allocations
for each free extent, and now we're up to three.  We need to get this
down to 1 and not increase it for no benefit.
Dave Chinner Aug. 4, 2016, 11:44 p.m. UTC | #8
On Thu, Aug 04, 2016 at 09:00:07AM -0700, Christoph Hellwig wrote:
> On Thu, Aug 04, 2016 at 08:57:56AM +1000, Dave Chinner wrote:
> > So, please explain in more detail what the problem is and what the
> > proposed solution is so I (and probably Darrick, too) have some
> > understanding of the issue you see with this code.
> 
> We were doing 1 (actually 2 with the busy extent tracking) allocations
> for each free extent, and now we're up to three.  We need to get this
> down to 1 and not increase it for no benefit.

Oh, it's memory allocations in the extent freeing path you're
worried about? That's a minor concern at this point, really. We do
some many other allocations in these paths (e.g. multiple
allocations for every metadata buffer that is not in cache) that
another is not going to make any difference to the system stability
or performance.

Yes, it would be good to reduce the number of allocations, but it's
not critical to the correct functioning of the code. hence it
doesn't need to be solved right now, and We can work on optimising
this over the next few months as we clean up all the rough edges we
find.

Cheers,

Dave.
diff mbox

Patch

diff --git a/fs/xfs/Makefile b/fs/xfs/Makefile
index 3542d94..01857b0 100644
--- a/fs/xfs/Makefile
+++ b/fs/xfs/Makefile
@@ -39,6 +39,7 @@  xfs-y				+= $(addprefix libxfs/, \
 				   xfs_btree.o \
 				   xfs_da_btree.o \
 				   xfs_da_format.o \
+				   xfs_defer.o \
 				   xfs_dir2.o \
 				   xfs_dir2_block.o \
 				   xfs_dir2_data.o \
diff --git a/fs/xfs/libxfs/xfs_defer.c b/fs/xfs/libxfs/xfs_defer.c
new file mode 100644
index 0000000..2809db7
--- /dev/null
+++ b/fs/xfs/libxfs/xfs_defer.c
@@ -0,0 +1,444 @@ 
+/*
+ * Copyright (C) 2016 Oracle.  All Rights Reserved.
+ *
+ * Author: Darrick J. Wong <darrick.wong@oracle.com>
+ *
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public License
+ * as published by the Free Software Foundation; either version 2
+ * of the License, or (at your option) any later version.
+ *
+ * This program is distributed in the hope that it would be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, write the Free Software Foundation,
+ * Inc.,  51 Franklin St, Fifth Floor, Boston, MA  02110-1301, USA.
+ */
+#include "xfs.h"
+#include "xfs_fs.h"
+#include "xfs_shared.h"
+#include "xfs_format.h"
+#include "xfs_log_format.h"
+#include "xfs_trans_resv.h"
+#include "xfs_bit.h"
+#include "xfs_sb.h"
+#include "xfs_mount.h"
+#include "xfs_defer.h"
+#include "xfs_trans.h"
+#include "xfs_trace.h"
+
+/*
+ * Deferred Operations in XFS
+ *
+ * Due to the way locking rules work in XFS, certain transactions (block
+ * mapping and unmapping, typically) have permanent reservations so that
+ * we can roll the transaction to adhere to AG locking order rules and
+ * to unlock buffers between metadata updates.  Prior to rmap/reflink,
+ * the mapping code had a mechanism to perform these deferrals for
+ * extents that were going to be freed; this code makes that facility
+ * more generic.
+ *
+ * When adding the reverse mapping and reflink features, it became
+ * necessary to perform complex remapping multi-transactions to comply
+ * with AG locking order rules, and to be able to spread a single
+ * refcount update operation (an operation on an n-block extent can
+ * update as many as n records!) among multiple transactions.  XFS can
+ * roll a transaction to facilitate this, but using this facility
+ * requires us to log "intent" items in case log recovery needs to
+ * redo the operation, and to log "done" items to indicate that redo
+ * is not necessary.
+ *
+ * Deferred work is tracked in xfs_defer_pending items.  Each pending
+ * item tracks one type of deferred work.  Incoming work items (which
+ * have not yet had an intent logged) are attached to a pending item
+ * on the dop_intake list, where they wait for the caller to finish
+ * the deferred operations.
+ *
+ * Finishing a set of deferred operations is an involved process.  To
+ * start, we define "rolling a deferred-op transaction" as follows:
+ *
+ * > For each xfs_defer_pending item on the dop_intake list,
+ *   - Sort the work items in AG order.  XFS locking
+ *     order rules require us to lock buffers in AG order.
+ *   - Create a log intent item for that type.
+ *   - Attach it to the pending item.
+ *   - Move the pending item from the dop_intake list to the
+ *     dop_pending list.
+ * > Roll the transaction.
+ *
+ * NOTE: To avoid exceeding the transaction reservation, we limit the
+ * number of items that we attach to a given xfs_defer_pending.
+ *
+ * The actual finishing process looks like this:
+ *
+ * > For each xfs_defer_pending in the dop_pending list,
+ *   - Roll the deferred-op transaction as above.
+ *   - Create a log done item for that type, and attach it to the
+ *     log intent item.
+ *   - For each work item attached to the log intent item,
+ *     * Perform the described action.
+ *     * Attach the work item to the log done item.
+ *
+ * The key here is that we must log an intent item for all pending
+ * work items every time we roll the transaction, and that we must log
+ * a done item as soon as the work is completed.  With this mechanism
+ * we can perform complex remapping operations, chaining intent items
+ * as needed.
+ *
+ * This is an example of remapping the extent (E, E+B) into file X at
+ * offset A and dealing with the extent (C, C+B) already being mapped
+ * there:
+ * +-------------------------------------------------+
+ * | Unmap file X startblock C offset A length B     | t0
+ * | Intent to reduce refcount for extent (C, B)     |
+ * | Intent to remove rmap (X, C, A, B)              |
+ * | Intent to free extent (D, 1) (bmbt block)       |
+ * | Intent to map (X, A, B) at startblock E         |
+ * +-------------------------------------------------+
+ * | Map file X startblock E offset A length B       | t1
+ * | Done mapping (X, E, A, B)                       |
+ * | Intent to increase refcount for extent (E, B)   |
+ * | Intent to add rmap (X, E, A, B)                 |
+ * +-------------------------------------------------+
+ * | Reduce refcount for extent (C, B)               | t2
+ * | Done reducing refcount for extent (C, B)        |
+ * | Increase refcount for extent (E, B)             |
+ * | Done increasing refcount for extent (E, B)      |
+ * | Intent to free extent (C, B)                    |
+ * | Intent to free extent (F, 1) (refcountbt block) |
+ * | Intent to remove rmap (F, 1, REFC)              |
+ * +-------------------------------------------------+
+ * | Remove rmap (X, C, A, B)                        | t3
+ * | Done removing rmap (X, C, A, B)                 |
+ * | Add rmap (X, E, A, B)                           |
+ * | Done adding rmap (X, E, A, B)                   |
+ * | Remove rmap (F, 1, REFC)                        |
+ * | Done removing rmap (F, 1, REFC)                 |
+ * +-------------------------------------------------+
+ * | Free extent (C, B)                              | t4
+ * | Done freeing extent (C, B)                      |
+ * | Free extent (D, 1)                              |
+ * | Done freeing extent (D, 1)                      |
+ * | Free extent (F, 1)                              |
+ * | Done freeing extent (F, 1)                      |
+ * +-------------------------------------------------+
+ *
+ * If we should crash before t2 commits, log recovery replays
+ * the following intent items:
+ *
+ * - Intent to reduce refcount for extent (C, B)
+ * - Intent to remove rmap (X, C, A, B)
+ * - Intent to free extent (D, 1) (bmbt block)
+ * - Intent to increase refcount for extent (E, B)
+ * - Intent to add rmap (X, E, A, B)
+ *
+ * In the process of recovering, it should also generate and take care
+ * of these intent items:
+ *
+ * - Intent to free extent (C, B)
+ * - Intent to free extent (F, 1) (refcountbt block)
+ * - Intent to remove rmap (F, 1, REFC)
+ */
+
+static const struct xfs_defer_op_type *defer_op_types[XFS_DEFER_OPS_TYPE_MAX];
+
+/*
+ * For each pending item in the intake list, log its intent item and the
+ * associated extents, then add the entire intake list to the end of
+ * the pending list.
+ */
+STATIC void
+xfs_defer_intake_work(
+	struct xfs_trans		*tp,
+	struct xfs_defer_ops		*dop)
+{
+	struct list_head		*li;
+	struct xfs_defer_pending	*dfp;
+
+	list_for_each_entry(dfp, &dop->dop_intake, dfp_list) {
+		dfp->dfp_intent = dfp->dfp_type->create_intent(tp,
+				dfp->dfp_count);
+		list_sort(tp->t_mountp, &dfp->dfp_work,
+				dfp->dfp_type->diff_items);
+		list_for_each(li, &dfp->dfp_work)
+			dfp->dfp_type->log_item(tp, dfp->dfp_intent, li);
+	}
+
+	list_splice_tail_init(&dop->dop_intake, &dop->dop_pending);
+}
+
+/* Abort all the intents that were committed. */
+STATIC void
+xfs_defer_trans_abort(
+	struct xfs_trans		*tp,
+	struct xfs_defer_ops		*dop,
+	int				error)
+{
+	struct xfs_defer_pending	*dfp;
+
+	/*
+	 * If the transaction was committed, drop the intent reference
+	 * since we're bailing out of here. The other reference is
+	 * dropped when the intent hits the AIL.  If the transaction
+	 * was not committed, the intent is freed by the intent item
+	 * unlock handler on abort.
+	 */
+	if (!dop->dop_committed)
+		return;
+
+	/* Abort intent items. */
+	list_for_each_entry(dfp, &dop->dop_pending, dfp_list) {
+		if (dfp->dfp_committed)
+			dfp->dfp_type->abort_intent(dfp->dfp_intent);
+	}
+
+	/* Shut down FS. */
+	xfs_force_shutdown(tp->t_mountp, (error == -EFSCORRUPTED) ?
+			SHUTDOWN_CORRUPT_INCORE : SHUTDOWN_META_IO_ERROR);
+}
+
+/* Roll a transaction so we can do some deferred op processing. */
+STATIC int
+xfs_defer_trans_roll(
+	struct xfs_trans		**tp,
+	struct xfs_defer_ops		*dop,
+	struct xfs_inode		*ip)
+{
+	int				i;
+	int				error;
+
+	/* Log all the joined inodes except the one we passed in. */
+	for (i = 0; i < XFS_DEFER_OPS_NR_INODES && dop->dop_inodes[i]; i++) {
+		if (dop->dop_inodes[i] == ip)
+			continue;
+		xfs_trans_log_inode(*tp, dop->dop_inodes[i], XFS_ILOG_CORE);
+	}
+
+	/* Roll the transaction. */
+	error = xfs_trans_roll(tp, ip);
+	if (error) {
+		xfs_defer_trans_abort(*tp, dop, error);
+		return error;
+	}
+	dop->dop_committed = true;
+
+	/* Rejoin the joined inodes except the one we passed in. */
+	for (i = 0; i < XFS_DEFER_OPS_NR_INODES && dop->dop_inodes[i]; i++) {
+		if (dop->dop_inodes[i] == ip)
+			continue;
+		xfs_trans_ijoin(*tp, dop->dop_inodes[i], 0);
+	}
+
+	return error;
+}
+
+/* Do we have any work items to finish? */
+bool
+xfs_defer_has_unfinished_work(
+	struct xfs_defer_ops		*dop)
+{
+	return !list_empty(&dop->dop_pending) || !list_empty(&dop->dop_intake);
+}
+
+/*
+ * Add this inode to the deferred op.  Each joined inode is relogged
+ * each time we roll the transaction, in addition to any inode passed
+ * to xfs_defer_finish().
+ */
+int
+xfs_defer_join(
+	struct xfs_defer_ops		*dop,
+	struct xfs_inode		*ip)
+{
+	int				i;
+
+	for (i = 0; i < XFS_DEFER_OPS_NR_INODES; i++) {
+		if (dop->dop_inodes[i] == ip)
+			return 0;
+		else if (dop->dop_inodes[i] == NULL) {
+			dop->dop_inodes[i] = ip;
+			return 0;
+		}
+	}
+
+	return -EFSCORRUPTED;
+}
+
+/*
+ * Finish all the pending work.  This involves logging intent items for
+ * any work items that wandered in since the last transaction roll (if
+ * one has even happened), rolling the transaction, and finishing the
+ * work items in the first item on the logged-and-pending list.
+ *
+ * If an inode is provided, relog it to the new transaction.
+ */
+int
+xfs_defer_finish(
+	struct xfs_trans		**tp,
+	struct xfs_defer_ops		*dop,
+	struct xfs_inode		*ip)
+{
+	struct xfs_defer_pending	*dfp;
+	struct list_head		*li;
+	struct list_head		*n;
+	void				*done_item = NULL;
+	void				*state;
+	int				error = 0;
+	void				(*cleanup_fn)(struct xfs_trans *, void *, int);
+
+	ASSERT((*tp)->t_flags & XFS_TRANS_PERM_LOG_RES);
+
+	/* Until we run out of pending work to finish... */
+	while (xfs_defer_has_unfinished_work(dop)) {
+		/* Log intents for work items sitting in the intake. */
+		xfs_defer_intake_work(*tp, dop);
+
+		/* Roll the transaction. */
+		error = xfs_defer_trans_roll(tp, dop, ip);
+		if (error)
+			goto out;
+
+		/* Mark all pending intents as committed. */
+		list_for_each_entry_reverse(dfp, &dop->dop_pending, dfp_list) {
+			if (dfp->dfp_committed)
+				break;
+			dfp->dfp_committed = true;
+		}
+
+		/* Log an intent-done item for the first pending item. */
+		dfp = list_first_entry(&dop->dop_pending,
+				struct xfs_defer_pending, dfp_list);
+		done_item = dfp->dfp_type->create_done(*tp, dfp->dfp_intent,
+				dfp->dfp_count);
+		cleanup_fn = dfp->dfp_type->finish_cleanup;
+
+		/* Finish the work items. */
+		state = NULL;
+		list_for_each_safe(li, n, &dfp->dfp_work) {
+			list_del(li);
+			dfp->dfp_count--;
+			error = dfp->dfp_type->finish_item(*tp, dop, li,
+					done_item, &state);
+			if (error) {
+				/*
+				 * Clean up after ourselves and jump out.
+				 * xfs_defer_cancel will take care of freeing
+				 * all these lists and stuff.
+				 */
+				if (cleanup_fn)
+					cleanup_fn(*tp, state, error);
+				xfs_defer_trans_abort(*tp, dop, error);
+				goto out;
+			}
+		}
+		/* Done with the dfp, free it. */
+		list_del(&dfp->dfp_list);
+		kmem_free(dfp);
+
+		if (cleanup_fn)
+			cleanup_fn(*tp, state, error);
+	}
+
+out:
+	return error;
+}
+
+/*
+ * Free up any items left in the list.
+ */
+void
+xfs_defer_cancel(
+	struct xfs_defer_ops		*dop)
+{
+	struct xfs_defer_pending	*dfp;
+	struct xfs_defer_pending	*pli;
+	struct list_head		*pwi;
+	struct list_head		*n;
+
+	/*
+	 * Free the pending items.  Caller should already have arranged
+	 * for the intent items to be released.
+	 */
+	list_for_each_entry_safe(dfp, pli, &dop->dop_intake, dfp_list) {
+		list_del(&dfp->dfp_list);
+		list_for_each_safe(pwi, n, &dfp->dfp_work) {
+			list_del(pwi);
+			dfp->dfp_count--;
+			dfp->dfp_type->cancel_item(pwi);
+		}
+		ASSERT(dfp->dfp_count == 0);
+		kmem_free(dfp);
+	}
+	list_for_each_entry_safe(dfp, pli, &dop->dop_pending, dfp_list) {
+		list_del(&dfp->dfp_list);
+		list_for_each_safe(pwi, n, &dfp->dfp_work) {
+			list_del(pwi);
+			dfp->dfp_count--;
+			dfp->dfp_type->cancel_item(pwi);
+		}
+		ASSERT(dfp->dfp_count == 0);
+		kmem_free(dfp);
+	}
+}
+
+/* Add an item for later deferred processing. */
+void
+xfs_defer_add(
+	struct xfs_defer_ops		*dop,
+	enum xfs_defer_ops_type		type,
+	struct list_head		*li)
+{
+	struct xfs_defer_pending	*dfp = NULL;
+
+	/*
+	 * Add the item to a pending item at the end of the intake list.
+	 * If the last pending item has the same type, reuse it.  Else,
+	 * create a new pending item at the end of the intake list.
+	 */
+	if (!list_empty(&dop->dop_intake)) {
+		dfp = list_last_entry(&dop->dop_intake,
+				struct xfs_defer_pending, dfp_list);
+		if (dfp->dfp_type->type != type ||
+		    (dfp->dfp_type->max_items &&
+		     dfp->dfp_count >= dfp->dfp_type->max_items))
+			dfp = NULL;
+	}
+	if (!dfp) {
+		dfp = kmem_alloc(sizeof(struct xfs_defer_pending),
+				KM_SLEEP | KM_NOFS);
+		dfp->dfp_type = defer_op_types[type];
+		dfp->dfp_committed = false;
+		dfp->dfp_intent = NULL;
+		dfp->dfp_count = 0;
+		INIT_LIST_HEAD(&dfp->dfp_work);
+		list_add_tail(&dfp->dfp_list, &dop->dop_intake);
+	}
+
+	list_add_tail(li, &dfp->dfp_work);
+	dfp->dfp_count++;
+}
+
+/* Initialize a deferred operation list. */
+void
+xfs_defer_init_op_type(
+	const struct xfs_defer_op_type	*type)
+{
+	defer_op_types[type->type] = type;
+}
+
+/* Initialize a deferred operation. */
+void
+xfs_defer_init(
+	struct xfs_defer_ops		*dop,
+	xfs_fsblock_t			*fbp)
+{
+	dop->dop_committed = false;
+	dop->dop_low = false;
+	memset(&dop->dop_inodes, 0, sizeof(dop->dop_inodes));
+	*fbp = NULLFSBLOCK;
+	INIT_LIST_HEAD(&dop->dop_intake);
+	INIT_LIST_HEAD(&dop->dop_pending);
+}
diff --git a/fs/xfs/libxfs/xfs_defer.h b/fs/xfs/libxfs/xfs_defer.h
new file mode 100644
index 0000000..a227bd2
--- /dev/null
+++ b/fs/xfs/libxfs/xfs_defer.h
@@ -0,0 +1,95 @@ 
+/*
+ * Copyright (C) 2016 Oracle.  All Rights Reserved.
+ *
+ * Author: Darrick J. Wong <darrick.wong@oracle.com>
+ *
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public License
+ * as published by the Free Software Foundation; either version 2
+ * of the License, or (at your option) any later version.
+ *
+ * This program is distributed in the hope that it would be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, write the Free Software Foundation,
+ * Inc.,  51 Franklin St, Fifth Floor, Boston, MA  02110-1301, USA.
+ */
+#ifndef __XFS_DEFER_H__
+#define	__XFS_DEFER_H__
+
+struct xfs_defer_op_type;
+
+/*
+ * Save a log intent item and a list of extents, so that we can replay
+ * whatever action had to happen to the extent list and file the log done
+ * item.
+ */
+struct xfs_defer_pending {
+	const struct xfs_defer_op_type	*dfp_type;	/* function pointers */
+	struct list_head		dfp_list;	/* pending items */
+	bool				dfp_committed;	/* committed trans? */
+	void				*dfp_intent;	/* log intent item */
+	struct list_head		dfp_work;	/* work items */
+	unsigned int			dfp_count;	/* # extent items */
+};
+
+/*
+ * Header for deferred operation list.
+ *
+ * dop_low is used by the allocator to activate the lowspace algorithm -
+ * when free space is running low the extent allocator may choose to
+ * allocate an extent from an AG without leaving sufficient space for
+ * a btree split when inserting the new extent.  In this case the allocator
+ * will enable the lowspace algorithm which is supposed to allow further
+ * allocations (such as btree splits and newroots) to allocate from
+ * sequential AGs.  In order to avoid locking AGs out of order the lowspace
+ * algorithm will start searching for free space from AG 0.  If the correct
+ * transaction reservations have been made then this algorithm will eventually
+ * find all the space it needs.
+ */
+enum xfs_defer_ops_type {
+	XFS_DEFER_OPS_TYPE_MAX,
+};
+
+#define XFS_DEFER_OPS_NR_INODES	2	/* join up to two inodes */
+
+struct xfs_defer_ops {
+	bool			dop_committed;	/* did any trans commit? */
+	bool			dop_low;	/* alloc in low mode */
+	struct list_head	dop_intake;	/* unlogged pending work */
+	struct list_head	dop_pending;	/* logged pending work */
+
+	/* relog these inodes with each roll */
+	struct xfs_inode	*dop_inodes[XFS_DEFER_OPS_NR_INODES];
+};
+
+void xfs_defer_add(struct xfs_defer_ops *dop, enum xfs_defer_ops_type type,
+		struct list_head *h);
+int xfs_defer_finish(struct xfs_trans **tp, struct xfs_defer_ops *dop,
+		struct xfs_inode *ip);
+void xfs_defer_cancel(struct xfs_defer_ops *dop);
+void xfs_defer_init(struct xfs_defer_ops *dop, xfs_fsblock_t *fbp);
+bool xfs_defer_has_unfinished_work(struct xfs_defer_ops *dop);
+int xfs_defer_join(struct xfs_defer_ops *dop, struct xfs_inode *ip);
+
+/* Description of a deferred type. */
+struct xfs_defer_op_type {
+	enum xfs_defer_ops_type	type;
+	unsigned int		max_items;
+	void (*abort_intent)(void *);
+	void *(*create_done)(struct xfs_trans *, void *, unsigned int);
+	int (*finish_item)(struct xfs_trans *, struct xfs_defer_ops *,
+			struct list_head *, void *, void **);
+	void (*finish_cleanup)(struct xfs_trans *, void *, int);
+	void (*cancel_item)(struct list_head *);
+	int (*diff_items)(void *, struct list_head *, struct list_head *);
+	void *(*create_intent)(struct xfs_trans *, uint);
+	void (*log_item)(struct xfs_trans *, void *, struct list_head *);
+};
+
+void xfs_defer_init_op_type(const struct xfs_defer_op_type *type);
+
+#endif /* __XFS_DEFER_H__ */