While removing a file with dedup extents, we could have a great number of delayed refs pending to process, and these refs refer to droping a ref of the extent, which is of BTRFS_DROP_DELAYED_REF type.
But in order to prevent an extent's ref count from going down to zero when there still are pending delayed refs, we first select those "adding a ref" ones, which is of BTRFS_ADD_DELAYED_REF type. So in removing case, all of our delayed refs are of BTRFS_DROP_DELAYED_REF type, but we have to walk all the refs issued to the extent to find any BTRFS_ADD_DELAYED_REF types and end up there is no such thing, and then start over again to find BTRFS_DROP_DELAYED_REF. This is really unnecessary, we can improve this by tracking how many BTRFS_ADD_DELAYED_REF refs we have and search by the right type. Signed-off-by: Liu Bo <bo.li....@oracle.com> --- fs/btrfs/delayed-ref.c | 8 ++++++++ fs/btrfs/delayed-ref.h | 3 +++ fs/btrfs/extent-tree.c | 16 +++++++++++++--- 3 files changed, 24 insertions(+), 3 deletions(-) diff --git a/fs/btrfs/delayed-ref.c b/fs/btrfs/delayed-ref.c index 3ab37b6..6435d78 100644 --- a/fs/btrfs/delayed-ref.c +++ b/fs/btrfs/delayed-ref.c @@ -538,6 +538,9 @@ update_existing_head_ref(struct btrfs_delayed_ref_node *existing, * currently, for refs we just added we know we're a-ok. */ existing->ref_mod += update->ref_mod; + WARN_ON(update->ref_mod > 1); + if (update->ref_mod == 1) + existing_ref->add_cnt++; spin_unlock(&existing_ref->lock); } @@ -601,6 +604,11 @@ add_delayed_ref_head(struct btrfs_fs_info *fs_info, head_ref->is_data = is_data; head_ref->ref_root = RB_ROOT; head_ref->processing = 0; + /* track added ref, more comments in select_delayed_ref() */ + if (count_mod == 1) + head_ref->add_cnt = 1; + else + head_ref->add_cnt = 0; spin_lock_init(&head_ref->lock); mutex_init(&head_ref->mutex); diff --git a/fs/btrfs/delayed-ref.h b/fs/btrfs/delayed-ref.h index 4ba9b93..905f991 100644 --- a/fs/btrfs/delayed-ref.h +++ b/fs/btrfs/delayed-ref.h @@ -87,6 +87,9 @@ struct btrfs_delayed_ref_head { struct rb_node href_node; struct btrfs_delayed_extent_op *extent_op; + + int add_cnt; + /* * when a new extent is allocated, it is just reserved in memory * The actual extent isn't inserted into the extent allocation tree diff --git a/fs/btrfs/extent-tree.c b/fs/btrfs/extent-tree.c index 088846c..191f0a7 100644 --- a/fs/btrfs/extent-tree.c +++ b/fs/btrfs/extent-tree.c @@ -2347,7 +2347,11 @@ static noinline struct btrfs_delayed_ref_node * select_delayed_ref(struct btrfs_delayed_ref_head *head) { struct rb_node *node; - struct btrfs_delayed_ref_node *ref, *last = NULL;; + struct btrfs_delayed_ref_node *ref, *last = NULL; + int action = BTRFS_ADD_DELAYED_REF; + + if (head->add_cnt == 0) + action = BTRFS_DROP_DELAYED_REF; /* * select delayed ref of type BTRFS_ADD_DELAYED_REF first. @@ -2358,10 +2362,13 @@ select_delayed_ref(struct btrfs_delayed_ref_head *head) while (node) { ref = rb_entry(node, struct btrfs_delayed_ref_node, rb_node); - if (ref->action == BTRFS_ADD_DELAYED_REF) + if (ref->action == action) { + if (ref->action == BTRFS_ADD_DELAYED_REF) + head->add_cnt--; return ref; - else if (last == NULL) + } else if (last == NULL) { last = ref; + } node = rb_next(node); } return last; @@ -2435,6 +2442,9 @@ static noinline int __btrfs_run_delayed_refs(struct btrfs_trans_handle *trans, if (ref && ref->seq && btrfs_check_delayed_seq(fs_info, delayed_refs, ref->seq)) { + if (ref->action == BTRFS_ADD_DELAYED_REF) + locked_ref->add_cnt++; + spin_unlock(&locked_ref->lock); btrfs_delayed_ref_unlock(locked_ref); spin_lock(&delayed_refs->lock); -- 1.8.1.4 -- To unsubscribe from this list: send the line "unsubscribe linux-btrfs" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html