On 2018/06/08 21:47, Nikolay Borisov wrote:
> This commit pulls those portions of the kernel implementation of
> delayed refs which are necessary to have them working in user-space.
> I've done the following modifications:
>
> 1. Replaced all kmem_cache_alloc calls to kmalloc.
>
> 2. Removed all locking-related code, since we are single threaded in
> userspace.
>
> 3. Removed code which deals with data refs - delayed refs in user space
> are going to be used only for cowonly trees.
>
> Signed-off-by: Nikolay Borisov <nborisov@xxxxxxxx>
> ---
> Makefile | 3 +-
> ctree.h | 3 +
> delayed-ref.c | 608 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
> delayed-ref.h | 225 ++++++++++++++++++++++
> extent-tree.c | 228 ++++++++++++++++++++++
> kerncompat.h | 8 +
> transaction.h | 4 +
> 7 files changed, 1078 insertions(+), 1 deletion(-)
> create mode 100644 delayed-ref.c
> create mode 100644 delayed-ref.h
>
> diff --git a/Makefile b/Makefile
> index 544410e6440c..9508ad4f11e6 100644
> --- a/Makefile
> +++ b/Makefile
> @@ -116,7 +116,8 @@ objects = ctree.o disk-io.o kernel-lib/radix-tree.o extent-tree.o print-tree.o \
> qgroup.o free-space-cache.o kernel-lib/list_sort.o props.o \
> kernel-shared/ulist.o qgroup-verify.o backref.o string-table.o task-utils.o \
> inode.o file.o find-root.o free-space-tree.o help.o send-dump.o \
> - fsfeatures.o kernel-lib/tables.o kernel-lib/raid56.o transaction.o
> + fsfeatures.o kernel-lib/tables.o kernel-lib/raid56.o transaction.o \
> + delayed-ref.o
> cmds_objects = cmds-subvolume.o cmds-filesystem.o cmds-device.o cmds-scrub.o \
> cmds-inspect.o cmds-balance.o cmds-send.o cmds-receive.o \
> cmds-quota.o cmds-qgroup.o cmds-replace.o check/main.o \
> diff --git a/ctree.h b/ctree.h
> index b30a946658ce..d1ea45571d1e 100644
> --- a/ctree.h
> +++ b/ctree.h
> @@ -2812,4 +2812,7 @@ int btrfs_punch_hole(struct btrfs_trans_handle *trans,
> int btrfs_read_file(struct btrfs_root *root, u64 ino, u64 start, int len,
> char *dest);
>
> +
> +/* extent-tree.c */
> +int btrfs_run_delayed_refs(struct btrfs_trans_handle *trans, unsigned long nr);
> #endif
> diff --git a/delayed-ref.c b/delayed-ref.c
> new file mode 100644
> index 000000000000..f3fa50239380
> --- /dev/null
> +++ b/delayed-ref.c
> @@ -0,0 +1,608 @@
<snip>
> +
> +static inline void drop_delayed_ref(struct btrfs_trans_handle *trans,
> + struct btrfs_delayed_ref_root *delayed_refs,
> + struct btrfs_delayed_ref_head *head,
> + struct btrfs_delayed_ref_node *ref)
> +{
> + rb_erase(&ref->ref_node, &head->ref_tree);
> + RB_CLEAR_NODE(&ref->ref_node);
> + if (!list_empty(&ref->add_list))
> + list_del(&ref->add_list);
> + ref->in_tree = 0;
> + btrfs_put_delayed_ref(ref);
Compared with kernel code, it seems that we need
delayed_refs->num_entries--;
> + if (trans->delayed_ref_updates)
> + trans->delayed_ref_updates--;
> +}
> +static noinline struct btrfs_delayed_ref_head *
> +add_delayed_ref_head(struct btrfs_trans_handle *trans,
> + struct btrfs_delayed_ref_head *head_ref,
> + void *qrecord,
> + int action, int *qrecord_inserted_ret,
> + int *old_ref_mod, int *new_ref_mod)
> +{
> + struct btrfs_delayed_ref_head *existing;
> + struct btrfs_delayed_ref_root *delayed_refs;
> +
> + delayed_refs = &trans->delayed_refs;
> +
> + existing = htree_insert(&delayed_refs->href_root, &head_ref->href_node);
> + if (existing) {
> + update_existing_head_ref(delayed_refs, existing, head_ref, old_ref_mod);
> + /*
> + * we've updated the existing ref, free the newly
> + * allocated ref
> + */
> + kfree(head_ref);
> + head_ref = existing;
> + } else {
> + if (old_ref_mod)
> + *old_ref_mod = 0;
> + delayed_refs->num_heads++;
> + delayed_refs->num_heads_ready++;
And
delayed_refs->num_entries++;
to correctly count num_entries.
(I noticed that num_entries went to negative value when I'm running gdb)
However, num_entries is actually not used in progs at all (it is used for
throttling in kernel), so maybe we can just drop the variable from progs?
> + trans->delayed_ref_updates++;
> + }
> + if (new_ref_mod)
> + *new_ref_mod = head_ref->total_ref_mod;
> +
> + return head_ref;
> +}
<snip>
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