On 11.06.2018 08:20, Qu Wenruo wrote:
>
>
> On 2018年06月08日 20:47, 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.
>
> That's pretty good, although still some data ref related
> structures/functions are left.
>
>>
>> Signed-off-by: Nikolay Borisov <nbori...@suse.com>
>> ---
>> 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 @@
>> +// SPDX-License-Identifier: GPL-2.0
>> +/*
>> + * Copyright (C) 2009 Oracle. All rights reserved.
>> + */
>> +
>> +#include "ctree.h"
>> +#include "btrfs-list.h"
>> +#include "delayed-ref.h"
>> +#include "transaction.h"
>> +
>> +/*
>> + * delayed back reference update tracking. For subvolume trees
>> + * we queue up extent allocations and backref maintenance for
>> + * delayed processing. This avoids deep call chains where we
>> + * add extents in the middle of btrfs_search_slot, and it allows
>> + * us to buffer up frequently modified backrefs in an rb tree instead
>> + * of hammering updates on the extent allocation tree.
>> + */
>
> A little more explanation on how delayed ref works will be more appricated.
I just copy/pasted that from the kernel code. TBH I'm not too familiar
with the backref lookup code to write something but I guess I can take a
look at it and perhaps add information to the btrfs-devs-docs. For now
I'm confident in my understanding of the delayed allocation/freeing logic.
>
> [snip]
>> +struct btrfs_delayed_tree_ref {
>> + struct btrfs_delayed_ref_node node;
>> + u64 root;
>> + u64 parent;
>> + int level;
>> +};
>> +
>> +struct btrfs_delayed_data_ref {
>> + struct btrfs_delayed_ref_node node;
>> + u64 root;
>> + u64 parent;
>> + u64 objectid;
>> + u64 offset;
>> +};
>
> Since we don't use this structure and don't support data ref yet, what
> about just removing this definiation?
Saw that tooand immediately sent v2 :)
>
> [snip]
>
>> +struct btrfs_delayed_ref_head *
>> +btrfs_select_ref_head(struct btrfs_trans_handle *trans);
>> +
>> +/*
>> + * helper functions to cast a node into its container
>> + */
>> +static inline struct btrfs_delayed_tree_ref *
>> +btrfs_delayed_node_to_tree_ref(struct btrfs_delayed_ref_node *node)
>> +{
>> + return container_of(node, struct btrfs_delayed_tree_ref, node);
>> +}
>> +
>> +static inline struct btrfs_delayed_data_ref *
>> +btrfs_delayed_node_to_data_ref(struct btrfs_delayed_ref_node *node)
>> +{
>> + return container_of(node, struct btrfs_delayed_data_ref, node);
>> +}
>
> So is the only user of btrfs_delayed_data_ref structure.
Fixed in v2
>
> Thanks,
> Qu
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