linux/fs/btrfs/backref.h
Filipe Manana adf0241868 btrfs: send: skip resolution of our own backref when finding clone source
When doing backref walking to determine a source range to clone from, it
is worthless to collect and resolve our own data backref, as we can't
obviously use it as a clone source and it represents the range we want to
clone into. Collecting the backref implies doing the extra work to resolve
it, doing the search for a file extent item in a subvolume tree, etc.
Skipping the data backref is valid as long as we only have the send root
as the single clone root, otherwise the leaf with the file extent item may
be accessible from another clone root due to shared subtrees created by
snapshots, and therefore we have to collect the backref and resolve it.

So add a callback to the backref walking code to guide it to skip data
backrefs.

This change is part of a patchset comprised of the following patches:

  01/17 btrfs: fix inode list leak during backref walking at resolve_indirect_refs()
  02/17 btrfs: fix inode list leak during backref walking at find_parent_nodes()
  03/17 btrfs: fix ulist leaks in error paths of qgroup self tests
  04/17 btrfs: remove pointless and double ulist frees in error paths of qgroup tests
  05/17 btrfs: send: avoid unnecessary path allocations when finding extent clone
  06/17 btrfs: send: update comment at find_extent_clone()
  07/17 btrfs: send: drop unnecessary backref context field initializations
  08/17 btrfs: send: avoid unnecessary backref lookups when finding clone source
  09/17 btrfs: send: optimize clone detection to increase extent sharing
  10/17 btrfs: use a single argument for extent offset in backref walking functions
  11/17 btrfs: use a structure to pass arguments to backref walking functions
  12/17 btrfs: reuse roots ulist on each leaf iteration for iterate_extent_inodes()
  13/17 btrfs: constify ulist parameter of ulist_next()
  14/17 btrfs: send: cache leaf to roots mapping during backref walking
  15/17 btrfs: send: skip unnecessary backref iterations
  16/17 btrfs: send: avoid double extent tree search when finding clone source
  17/17 btrfs: send: skip resolution of our own backref when finding clone source

The following test was run on non-debug kernel (Debian's default kernel
config) before and after applying the patchset:

   $ cat test-send-many-shared-extents.sh
   #!/bin/bash

   DEV=/dev/sdh
   MNT=/mnt/sdh

   umount $DEV &> /dev/null
   mkfs.btrfs -f $DEV
   mount $DEV $MNT

   num_files=50000
   num_clones_per_file=50

   for ((i = 1; i <= $num_files; i++)); do
       xfs_io -f -c "pwrite 0 64K" $MNT/file_$i > /dev/null
       echo -ne "\r$i files created..."
   done
   echo

   btrfs subvolume snapshot -r $MNT $MNT/snap1

   cloned=0
   for ((i = 1; i <= $num_clones_per_file; i++)); do
       for ((j = 1; j <= $num_files; j++)); do
           cp --reflink=always $MNT/file_$j $MNT/file_${j}_clone_${i}
           cloned=$((cloned + 1))
           echo -ne "\r$cloned / $((num_files * num_clones_per_file)) clone operations"
       done
   done
   echo

   btrfs subvolume snapshot -r $MNT $MNT/snap2

   # Unmount and mount again to clear all cached metadata (and data).
   umount $DEV
   mount $DEV $MNT

   start=$(date +%s%N)
   btrfs send $MNT/snap2 > /dev/null
   end=$(date +%s%N)

   dur=$(( (end - start) / 1000000000 ))
   echo -e "\nFull send took $dur seconds"

   # Unmount and mount again to clear all cached metadata (and data).
   umount $DEV
   mount $DEV $MNT

   start=$(date +%s%N)
   btrfs send -p $MNT/snap1 $MNT/snap2 > /dev/null
   end=$(date +%s%N)

   dur=$(( (end - start) / 1000000000 ))
   echo -e "\nIncremental send took $dur seconds"

   umount $MNT

Before applying the patchset:

   (...)
   Full send took 1108 seconds
   (...)
   Incremental send took 1135 seconds

After applying the whole patchset:

   (...)
   Full send took 268 seconds            (-75.8%)
   (...)
   Incremental send took 316 seconds     (-72.2%)

Signed-off-by: Filipe Manana <fdmanana@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>
2022-12-05 18:00:50 +01:00

550 lines
17 KiB
C

/* SPDX-License-Identifier: GPL-2.0 */
/*
* Copyright (C) 2011 STRATO. All rights reserved.
*/
#ifndef BTRFS_BACKREF_H
#define BTRFS_BACKREF_H
#include <linux/btrfs.h>
#include "messages.h"
#include "ulist.h"
#include "disk-io.h"
#include "extent_io.h"
/*
* Used by implementations of iterate_extent_inodes_t (see definition below) to
* signal that backref iteration can stop immediately and no error happened.
* The value must be non-negative and must not be 0, 1 (which is a common return
* value from things like btrfs_search_slot() and used internally in the backref
* walking code) and different from BACKREF_FOUND_SHARED and
* BACKREF_FOUND_NOT_SHARED
*/
#define BTRFS_ITERATE_EXTENT_INODES_STOP 5
/*
* Should return 0 if no errors happened and iteration of backrefs should
* continue. Can return BTRFS_ITERATE_EXTENT_INODES_STOP or any other non-zero
* value to immediately stop iteration and possibly signal an error back to
* the caller.
*/
typedef int (iterate_extent_inodes_t)(u64 inum, u64 offset, u64 num_bytes,
u64 root, void *ctx);
/*
* Context and arguments for backref walking functions. Some of the fields are
* to be filled by the caller of such functions while other are filled by the
* functions themselves, as described below.
*/
struct btrfs_backref_walk_ctx {
/*
* The address of the extent for which we are doing backref walking.
* Can be either a data extent or a metadata extent.
*
* Must always be set by the top level caller.
*/
u64 bytenr;
/*
* Offset relative to the target extent. This is only used for data
* extents, and it's meaningful because we can have file extent items
* that point only to a section of a data extent ("bookend" extents),
* and we want to filter out any that don't point to a section of the
* data extent containing the given offset.
*
* Must always be set by the top level caller.
*/
u64 extent_item_pos;
/*
* If true and bytenr corresponds to a data extent, then references from
* all file extent items that point to the data extent are considered,
* @extent_item_pos is ignored.
*/
bool ignore_extent_item_pos;
/* A valid transaction handle or NULL. */
struct btrfs_trans_handle *trans;
/*
* The file system's info object, can not be NULL.
*
* Must always be set by the top level caller.
*/
struct btrfs_fs_info *fs_info;
/*
* Time sequence acquired from btrfs_get_tree_mod_seq(), in case the
* caller joined the tree mod log to get a consistent view of b+trees
* while we do backref walking, or BTRFS_SEQ_LAST.
* When using BTRFS_SEQ_LAST, delayed refs are not checked and it uses
* commit roots when searching b+trees - this is a special case for
* qgroups used during a transaction commit.
*/
u64 time_seq;
/*
* Used to collect the bytenr of metadata extents that point to the
* target extent.
*/
struct ulist *refs;
/*
* List used to collect the IDs of the roots from which the target
* extent is accessible. Can be NULL in case the caller does not care
* about collecting root IDs.
*/
struct ulist *roots;
/*
* Used by iterate_extent_inodes() and the main backref walk code
* (find_parent_nodes()). Lookup and store functions for an optional
* cache which maps the logical address (bytenr) of leaves to an array
* of root IDs.
*/
bool (*cache_lookup)(u64 leaf_bytenr, void *user_ctx,
const u64 **root_ids_ret, int *root_count_ret);
void (*cache_store)(u64 leaf_bytenr, const struct ulist *root_ids,
void *user_ctx);
/*
* If this is not NULL, then the backref walking code will call this
* for each indirect data extent reference as soon as it finds one,
* before collecting all the remaining backrefs and before resolving
* indirect backrefs. This allows for the caller to terminate backref
* walking as soon as it finds one backref that matches some specific
* criteria. The @cache_lookup and @cache_store callbacks should not
* be NULL in order to use this callback.
*/
iterate_extent_inodes_t *indirect_ref_iterator;
/*
* If this is not NULL, then the backref walking code will call this for
* each extent item it's meant to process before it actually starts
* processing it. If this returns anything other than 0, then it stops
* the backref walking code immediately.
*/
int (*check_extent_item)(u64 bytenr, const struct btrfs_extent_item *ei,
const struct extent_buffer *leaf, void *user_ctx);
/*
* If this is not NULL, then the backref walking code will call this for
* each extent data ref it finds (BTRFS_EXTENT_DATA_REF_KEY keys) before
* processing that data ref. If this callback return false, then it will
* ignore this data ref and it will never resolve the indirect data ref,
* saving time searching for leaves in a fs tree with file extent items
* matching the data ref.
*/
bool (*skip_data_ref)(u64 root, u64 ino, u64 offset, void *user_ctx);
/* Context object to pass to the callbacks defined above. */
void *user_ctx;
};
struct inode_fs_paths {
struct btrfs_path *btrfs_path;
struct btrfs_root *fs_root;
struct btrfs_data_container *fspath;
};
struct btrfs_backref_shared_cache_entry {
u64 bytenr;
u64 gen;
bool is_shared;
};
#define BTRFS_BACKREF_CTX_PREV_EXTENTS_SIZE 8
struct btrfs_backref_share_check_ctx {
/* Ulists used during backref walking. */
struct ulist refs;
/*
* The current leaf the caller of btrfs_is_data_extent_shared() is at.
* Typically the caller (at the moment only fiemap) tries to determine
* the sharedness of data extents point by file extent items from entire
* leaves.
*/
u64 curr_leaf_bytenr;
/*
* The previous leaf the caller was at in the previous call to
* btrfs_is_data_extent_shared(). This may be the same as the current
* leaf. On the first call it must be 0.
*/
u64 prev_leaf_bytenr;
/*
* A path from a root to a leaf that has a file extent item pointing to
* a given data extent should never exceed the maximum b+tree height.
*/
struct btrfs_backref_shared_cache_entry path_cache_entries[BTRFS_MAX_LEVEL];
bool use_path_cache;
/*
* Cache the sharedness result for the last few extents we have found,
* but only for extents for which we have multiple file extent items
* that point to them.
* It's very common to have several file extent items that point to the
* same extent (bytenr) but with different offsets and lengths. This
* typically happens for COW writes, partial writes into prealloc
* extents, NOCOW writes after snapshoting a root, hole punching or
* reflinking within the same file (less common perhaps).
* So keep a small cache with the lookup results for the extent pointed
* by the last few file extent items. This cache is checked, with a
* linear scan, whenever btrfs_is_data_extent_shared() is called, so
* it must be small so that it does not negatively affect performance in
* case we don't have multiple file extent items that point to the same
* data extent.
*/
struct {
u64 bytenr;
bool is_shared;
} prev_extents_cache[BTRFS_BACKREF_CTX_PREV_EXTENTS_SIZE];
/*
* The slot in the prev_extents_cache array that will be used for
* storing the sharedness result of a new data extent.
*/
int prev_extents_cache_slot;
};
struct btrfs_backref_share_check_ctx *btrfs_alloc_backref_share_check_ctx(void);
void btrfs_free_backref_share_ctx(struct btrfs_backref_share_check_ctx *ctx);
int extent_from_logical(struct btrfs_fs_info *fs_info, u64 logical,
struct btrfs_path *path, struct btrfs_key *found_key,
u64 *flags);
int tree_backref_for_extent(unsigned long *ptr, struct extent_buffer *eb,
struct btrfs_key *key, struct btrfs_extent_item *ei,
u32 item_size, u64 *out_root, u8 *out_level);
int iterate_extent_inodes(struct btrfs_backref_walk_ctx *ctx,
bool search_commit_root,
iterate_extent_inodes_t *iterate, void *user_ctx);
int iterate_inodes_from_logical(u64 logical, struct btrfs_fs_info *fs_info,
struct btrfs_path *path, void *ctx,
bool ignore_offset);
int paths_from_inode(u64 inum, struct inode_fs_paths *ipath);
int btrfs_find_all_leafs(struct btrfs_backref_walk_ctx *ctx);
int btrfs_find_all_roots(struct btrfs_backref_walk_ctx *ctx,
bool skip_commit_root_sem);
char *btrfs_ref_to_path(struct btrfs_root *fs_root, struct btrfs_path *path,
u32 name_len, unsigned long name_off,
struct extent_buffer *eb_in, u64 parent,
char *dest, u32 size);
struct btrfs_data_container *init_data_container(u32 total_bytes);
struct inode_fs_paths *init_ipath(s32 total_bytes, struct btrfs_root *fs_root,
struct btrfs_path *path);
void free_ipath(struct inode_fs_paths *ipath);
int btrfs_find_one_extref(struct btrfs_root *root, u64 inode_objectid,
u64 start_off, struct btrfs_path *path,
struct btrfs_inode_extref **ret_extref,
u64 *found_off);
int btrfs_is_data_extent_shared(struct btrfs_inode *inode, u64 bytenr,
u64 extent_gen,
struct btrfs_backref_share_check_ctx *ctx);
int __init btrfs_prelim_ref_init(void);
void __cold btrfs_prelim_ref_exit(void);
struct prelim_ref {
struct rb_node rbnode;
u64 root_id;
struct btrfs_key key_for_search;
int level;
int count;
struct extent_inode_elem *inode_list;
u64 parent;
u64 wanted_disk_byte;
};
/*
* Iterate backrefs of one extent.
*
* Now it only supports iteration of tree block in commit root.
*/
struct btrfs_backref_iter {
u64 bytenr;
struct btrfs_path *path;
struct btrfs_fs_info *fs_info;
struct btrfs_key cur_key;
u32 item_ptr;
u32 cur_ptr;
u32 end_ptr;
};
struct btrfs_backref_iter *btrfs_backref_iter_alloc(struct btrfs_fs_info *fs_info);
static inline void btrfs_backref_iter_free(struct btrfs_backref_iter *iter)
{
if (!iter)
return;
btrfs_free_path(iter->path);
kfree(iter);
}
static inline struct extent_buffer *btrfs_backref_get_eb(
struct btrfs_backref_iter *iter)
{
if (!iter)
return NULL;
return iter->path->nodes[0];
}
/*
* For metadata with EXTENT_ITEM key (non-skinny) case, the first inline data
* is btrfs_tree_block_info, without a btrfs_extent_inline_ref header.
*
* This helper determines if that's the case.
*/
static inline bool btrfs_backref_has_tree_block_info(
struct btrfs_backref_iter *iter)
{
if (iter->cur_key.type == BTRFS_EXTENT_ITEM_KEY &&
iter->cur_ptr - iter->item_ptr == sizeof(struct btrfs_extent_item))
return true;
return false;
}
int btrfs_backref_iter_start(struct btrfs_backref_iter *iter, u64 bytenr);
int btrfs_backref_iter_next(struct btrfs_backref_iter *iter);
static inline bool btrfs_backref_iter_is_inline_ref(
struct btrfs_backref_iter *iter)
{
if (iter->cur_key.type == BTRFS_EXTENT_ITEM_KEY ||
iter->cur_key.type == BTRFS_METADATA_ITEM_KEY)
return true;
return false;
}
static inline void btrfs_backref_iter_release(struct btrfs_backref_iter *iter)
{
iter->bytenr = 0;
iter->item_ptr = 0;
iter->cur_ptr = 0;
iter->end_ptr = 0;
btrfs_release_path(iter->path);
memset(&iter->cur_key, 0, sizeof(iter->cur_key));
}
/*
* Backref cache related structures
*
* The whole objective of backref_cache is to build a bi-directional map
* of tree blocks (represented by backref_node) and all their parents.
*/
/*
* Represent a tree block in the backref cache
*/
struct btrfs_backref_node {
struct {
struct rb_node rb_node;
u64 bytenr;
}; /* Use rb_simple_node for search/insert */
u64 new_bytenr;
/* Objectid of tree block owner, can be not uptodate */
u64 owner;
/* Link to pending, changed or detached list */
struct list_head list;
/* List of upper level edges, which link this node to its parents */
struct list_head upper;
/* List of lower level edges, which link this node to its children */
struct list_head lower;
/* NULL if this node is not tree root */
struct btrfs_root *root;
/* Extent buffer got by COWing the block */
struct extent_buffer *eb;
/* Level of the tree block */
unsigned int level:8;
/* Is the block in a non-shareable tree */
unsigned int cowonly:1;
/* 1 if no child node is in the cache */
unsigned int lowest:1;
/* Is the extent buffer locked */
unsigned int locked:1;
/* Has the block been processed */
unsigned int processed:1;
/* Have backrefs of this block been checked */
unsigned int checked:1;
/*
* 1 if corresponding block has been COWed but some upper level block
* pointers may not point to the new location
*/
unsigned int pending:1;
/* 1 if the backref node isn't connected to any other backref node */
unsigned int detached:1;
/*
* For generic purpose backref cache, where we only care if it's a reloc
* root, doesn't care the source subvolid.
*/
unsigned int is_reloc_root:1;
};
#define LOWER 0
#define UPPER 1
/*
* Represent an edge connecting upper and lower backref nodes.
*/
struct btrfs_backref_edge {
/*
* list[LOWER] is linked to btrfs_backref_node::upper of lower level
* node, and list[UPPER] is linked to btrfs_backref_node::lower of
* upper level node.
*
* Also, build_backref_tree() uses list[UPPER] for pending edges, before
* linking list[UPPER] to its upper level nodes.
*/
struct list_head list[2];
/* Two related nodes */
struct btrfs_backref_node *node[2];
};
struct btrfs_backref_cache {
/* Red black tree of all backref nodes in the cache */
struct rb_root rb_root;
/* For passing backref nodes to btrfs_reloc_cow_block */
struct btrfs_backref_node *path[BTRFS_MAX_LEVEL];
/*
* List of blocks that have been COWed but some block pointers in upper
* level blocks may not reflect the new location
*/
struct list_head pending[BTRFS_MAX_LEVEL];
/* List of backref nodes with no child node */
struct list_head leaves;
/* List of blocks that have been COWed in current transaction */
struct list_head changed;
/* List of detached backref node. */
struct list_head detached;
u64 last_trans;
int nr_nodes;
int nr_edges;
/* List of unchecked backref edges during backref cache build */
struct list_head pending_edge;
/* List of useless backref nodes during backref cache build */
struct list_head useless_node;
struct btrfs_fs_info *fs_info;
/*
* Whether this cache is for relocation
*
* Reloction backref cache require more info for reloc root compared
* to generic backref cache.
*/
unsigned int is_reloc;
};
void btrfs_backref_init_cache(struct btrfs_fs_info *fs_info,
struct btrfs_backref_cache *cache, int is_reloc);
struct btrfs_backref_node *btrfs_backref_alloc_node(
struct btrfs_backref_cache *cache, u64 bytenr, int level);
struct btrfs_backref_edge *btrfs_backref_alloc_edge(
struct btrfs_backref_cache *cache);
#define LINK_LOWER (1 << 0)
#define LINK_UPPER (1 << 1)
static inline void btrfs_backref_link_edge(struct btrfs_backref_edge *edge,
struct btrfs_backref_node *lower,
struct btrfs_backref_node *upper,
int link_which)
{
ASSERT(upper && lower && upper->level == lower->level + 1);
edge->node[LOWER] = lower;
edge->node[UPPER] = upper;
if (link_which & LINK_LOWER)
list_add_tail(&edge->list[LOWER], &lower->upper);
if (link_which & LINK_UPPER)
list_add_tail(&edge->list[UPPER], &upper->lower);
}
static inline void btrfs_backref_free_node(struct btrfs_backref_cache *cache,
struct btrfs_backref_node *node)
{
if (node) {
ASSERT(list_empty(&node->list));
ASSERT(list_empty(&node->lower));
ASSERT(node->eb == NULL);
cache->nr_nodes--;
btrfs_put_root(node->root);
kfree(node);
}
}
static inline void btrfs_backref_free_edge(struct btrfs_backref_cache *cache,
struct btrfs_backref_edge *edge)
{
if (edge) {
cache->nr_edges--;
kfree(edge);
}
}
static inline void btrfs_backref_unlock_node_buffer(
struct btrfs_backref_node *node)
{
if (node->locked) {
btrfs_tree_unlock(node->eb);
node->locked = 0;
}
}
static inline void btrfs_backref_drop_node_buffer(
struct btrfs_backref_node *node)
{
if (node->eb) {
btrfs_backref_unlock_node_buffer(node);
free_extent_buffer(node->eb);
node->eb = NULL;
}
}
/*
* Drop the backref node from cache without cleaning up its children
* edges.
*
* This can only be called on node without parent edges.
* The children edges are still kept as is.
*/
static inline void btrfs_backref_drop_node(struct btrfs_backref_cache *tree,
struct btrfs_backref_node *node)
{
ASSERT(list_empty(&node->upper));
btrfs_backref_drop_node_buffer(node);
list_del_init(&node->list);
list_del_init(&node->lower);
if (!RB_EMPTY_NODE(&node->rb_node))
rb_erase(&node->rb_node, &tree->rb_root);
btrfs_backref_free_node(tree, node);
}
void btrfs_backref_cleanup_node(struct btrfs_backref_cache *cache,
struct btrfs_backref_node *node);
void btrfs_backref_release_cache(struct btrfs_backref_cache *cache);
static inline void btrfs_backref_panic(struct btrfs_fs_info *fs_info,
u64 bytenr, int errno)
{
btrfs_panic(fs_info, errno,
"Inconsistency in backref cache found at offset %llu",
bytenr);
}
int btrfs_backref_add_tree_node(struct btrfs_backref_cache *cache,
struct btrfs_path *path,
struct btrfs_backref_iter *iter,
struct btrfs_key *node_key,
struct btrfs_backref_node *cur);
int btrfs_backref_finish_upper_links(struct btrfs_backref_cache *cache,
struct btrfs_backref_node *start);
void btrfs_backref_error_cleanup(struct btrfs_backref_cache *cache,
struct btrfs_backref_node *node);
#endif