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

Brian Foster
2016-08-02T17:30:25Z

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