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![Jan Schmidt](/assets/img/avatar_default.png)
Now that we may be holding back delayed refs for a limited period, we might end up having no runnable delayed refs. Without this commit, we'd do busy waiting in that thread until another (runnable) ref arives. Instead, we're detecting this situation and use a waitqueue, such that we only try to run more refs after a) another runnable ref was added or b) delayed refs are no longer held back Signed-off-by: Jan Schmidt <list.btrfs@jan-o-sch.net>
283 lines
8 KiB
C
283 lines
8 KiB
C
/*
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* Copyright (C) 2008 Oracle. All rights reserved.
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*
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* This program is free software; you can redistribute it and/or
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* modify it under the terms of the GNU General Public
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* License v2 as published by the Free Software Foundation.
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*
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* This program is distributed in the hope that it will be useful,
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* but WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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* General Public License for more details.
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*
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* You should have received a copy of the GNU General Public
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* License along with this program; if not, write to the
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* Free Software Foundation, Inc., 59 Temple Place - Suite 330,
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* Boston, MA 021110-1307, USA.
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*/
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#ifndef __DELAYED_REF__
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#define __DELAYED_REF__
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/* these are the possible values of struct btrfs_delayed_ref->action */
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#define BTRFS_ADD_DELAYED_REF 1 /* add one backref to the tree */
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#define BTRFS_DROP_DELAYED_REF 2 /* delete one backref from the tree */
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#define BTRFS_ADD_DELAYED_EXTENT 3 /* record a full extent allocation */
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#define BTRFS_UPDATE_DELAYED_HEAD 4 /* not changing ref count on head ref */
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struct btrfs_delayed_ref_node {
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struct rb_node rb_node;
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/* the starting bytenr of the extent */
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u64 bytenr;
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/* the size of the extent */
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u64 num_bytes;
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/* seq number to keep track of insertion order */
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u64 seq;
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/* ref count on this data structure */
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atomic_t refs;
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/*
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* how many refs is this entry adding or deleting. For
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* head refs, this may be a negative number because it is keeping
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* track of the total mods done to the reference count.
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* For individual refs, this will always be a positive number
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*
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* It may be more than one, since it is possible for a single
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* parent to have more than one ref on an extent
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*/
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int ref_mod;
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unsigned int action:8;
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unsigned int type:8;
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/* is this node still in the rbtree? */
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unsigned int is_head:1;
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unsigned int in_tree:1;
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};
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struct btrfs_delayed_extent_op {
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struct btrfs_disk_key key;
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u64 flags_to_set;
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unsigned int update_key:1;
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unsigned int update_flags:1;
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unsigned int is_data:1;
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};
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/*
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* the head refs are used to hold a lock on a given extent, which allows us
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* to make sure that only one process is running the delayed refs
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* at a time for a single extent. They also store the sum of all the
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* reference count modifications we've queued up.
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*/
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struct btrfs_delayed_ref_head {
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struct btrfs_delayed_ref_node node;
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/*
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* the mutex is held while running the refs, and it is also
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* held when checking the sum of reference modifications.
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*/
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struct mutex mutex;
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struct list_head cluster;
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struct btrfs_delayed_extent_op *extent_op;
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/*
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* when a new extent is allocated, it is just reserved in memory
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* The actual extent isn't inserted into the extent allocation tree
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* until the delayed ref is processed. must_insert_reserved is
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* used to flag a delayed ref so the accounting can be updated
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* when a full insert is done.
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*
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* It is possible the extent will be freed before it is ever
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* inserted into the extent allocation tree. In this case
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* we need to update the in ram accounting to properly reflect
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* the free has happened.
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*/
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unsigned int must_insert_reserved:1;
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unsigned int is_data:1;
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};
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struct btrfs_delayed_tree_ref {
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struct btrfs_delayed_ref_node node;
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u64 root;
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u64 parent;
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int level;
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};
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struct btrfs_delayed_data_ref {
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struct btrfs_delayed_ref_node node;
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u64 root;
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u64 parent;
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u64 objectid;
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u64 offset;
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};
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struct btrfs_delayed_ref_root {
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struct rb_root root;
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/* this spin lock protects the rbtree and the entries inside */
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spinlock_t lock;
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/* how many delayed ref updates we've queued, used by the
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* throttling code
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*/
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unsigned long num_entries;
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/* total number of head nodes in tree */
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unsigned long num_heads;
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/* total number of head nodes ready for processing */
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unsigned long num_heads_ready;
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/*
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* set when the tree is flushing before a transaction commit,
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* used by the throttling code to decide if new updates need
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* to be run right away
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*/
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int flushing;
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u64 run_delayed_start;
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/*
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* seq number of delayed refs. We need to know if a backref was being
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* added before the currently processed ref or afterwards.
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*/
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u64 seq;
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/*
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* seq_list holds a list of all seq numbers that are currently being
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* added to the list. While walking backrefs (btrfs_find_all_roots,
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* qgroups), which might take some time, no newer ref must be processed,
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* as it might influence the outcome of the walk.
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*/
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struct list_head seq_head;
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/*
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* when the only refs we have in the list must not be processed, we want
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* to wait for more refs to show up or for the end of backref walking.
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*/
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wait_queue_head_t seq_wait;
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};
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static inline void btrfs_put_delayed_ref(struct btrfs_delayed_ref_node *ref)
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{
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WARN_ON(atomic_read(&ref->refs) == 0);
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if (atomic_dec_and_test(&ref->refs)) {
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WARN_ON(ref->in_tree);
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kfree(ref);
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}
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}
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int btrfs_add_delayed_tree_ref(struct btrfs_fs_info *fs_info,
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struct btrfs_trans_handle *trans,
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u64 bytenr, u64 num_bytes, u64 parent,
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u64 ref_root, int level, int action,
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struct btrfs_delayed_extent_op *extent_op,
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int for_cow);
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int btrfs_add_delayed_data_ref(struct btrfs_fs_info *fs_info,
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struct btrfs_trans_handle *trans,
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u64 bytenr, u64 num_bytes,
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u64 parent, u64 ref_root,
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u64 owner, u64 offset, int action,
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struct btrfs_delayed_extent_op *extent_op,
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int for_cow);
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int btrfs_add_delayed_extent_op(struct btrfs_fs_info *fs_info,
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struct btrfs_trans_handle *trans,
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u64 bytenr, u64 num_bytes,
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struct btrfs_delayed_extent_op *extent_op);
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struct btrfs_delayed_ref_head *
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btrfs_find_delayed_ref_head(struct btrfs_trans_handle *trans, u64 bytenr);
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int btrfs_delayed_ref_lock(struct btrfs_trans_handle *trans,
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struct btrfs_delayed_ref_head *head);
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int btrfs_find_ref_cluster(struct btrfs_trans_handle *trans,
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struct list_head *cluster, u64 search_start);
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struct seq_list {
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struct list_head list;
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u64 seq;
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};
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static inline u64 inc_delayed_seq(struct btrfs_delayed_ref_root *delayed_refs)
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{
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assert_spin_locked(&delayed_refs->lock);
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++delayed_refs->seq;
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return delayed_refs->seq;
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}
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static inline void
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btrfs_get_delayed_seq(struct btrfs_delayed_ref_root *delayed_refs,
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struct seq_list *elem)
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{
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assert_spin_locked(&delayed_refs->lock);
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elem->seq = delayed_refs->seq;
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list_add_tail(&elem->list, &delayed_refs->seq_head);
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}
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static inline void
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btrfs_put_delayed_seq(struct btrfs_delayed_ref_root *delayed_refs,
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struct seq_list *elem)
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{
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spin_lock(&delayed_refs->lock);
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list_del(&elem->list);
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wake_up(&delayed_refs->seq_wait);
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spin_unlock(&delayed_refs->lock);
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}
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int btrfs_check_delayed_seq(struct btrfs_delayed_ref_root *delayed_refs,
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u64 seq);
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/*
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* delayed refs with a ref_seq > 0 must be held back during backref walking.
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* this only applies to items in one of the fs-trees. for_cow items never need
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* to be held back, so they won't get a ref_seq number.
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*/
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static inline int need_ref_seq(int for_cow, u64 rootid)
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{
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if (for_cow)
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return 0;
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if (rootid == BTRFS_FS_TREE_OBJECTID)
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return 1;
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if ((s64)rootid >= (s64)BTRFS_FIRST_FREE_OBJECTID)
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return 1;
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return 0;
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}
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/*
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* a node might live in a head or a regular ref, this lets you
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* test for the proper type to use.
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*/
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static int btrfs_delayed_ref_is_head(struct btrfs_delayed_ref_node *node)
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{
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return node->is_head;
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}
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/*
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* helper functions to cast a node into its container
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*/
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static inline struct btrfs_delayed_tree_ref *
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btrfs_delayed_node_to_tree_ref(struct btrfs_delayed_ref_node *node)
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{
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WARN_ON(btrfs_delayed_ref_is_head(node));
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return container_of(node, struct btrfs_delayed_tree_ref, node);
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}
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static inline struct btrfs_delayed_data_ref *
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btrfs_delayed_node_to_data_ref(struct btrfs_delayed_ref_node *node)
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{
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WARN_ON(btrfs_delayed_ref_is_head(node));
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return container_of(node, struct btrfs_delayed_data_ref, node);
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}
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static inline struct btrfs_delayed_ref_head *
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btrfs_delayed_node_to_head(struct btrfs_delayed_ref_node *node)
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{
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WARN_ON(!btrfs_delayed_ref_is_head(node));
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return container_of(node, struct btrfs_delayed_ref_head, node);
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}
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#endif
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