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Btrfs: don't preallocate metadata blocks during btrfs_search_slot
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In order to avoid doing expensive extent management with tree locks held,
btrfs_search_slot will preallocate tree blocks for use by COW without
any tree locks held.

A later commit moves all of the extent allocation work for COW into
a delayed update mechanism, and this preallocation will no longer be
required.

Signed-off-by: Chris Mason <chris.mason@oracle.com>
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Chris Mason committed Mar 24, 2009
1 parent 8e0ee43 commit 9fa8cfe
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Showing 3 changed files with 21 additions and 85 deletions.
100 changes: 18 additions & 82 deletions fs/btrfs/ctree.c
View file
Original file line number Diff line number Diff line change
Expand Up @@ -254,18 +254,13 @@ int btrfs_copy_root(struct btrfs_trans_handle *trans,
* empty_size -- a hint that you plan on doing more cow. This is the size in
* bytes the allocator should try to find free next to the block it returns.
* This is just a hint and may be ignored by the allocator.
*
* prealloc_dest -- if you have already reserved a destination for the cow,
* this uses that block instead of allocating a new one.
* btrfs_alloc_reserved_extent is used to finish the allocation.
*/
static noinline int __btrfs_cow_block(struct btrfs_trans_handle *trans,
struct btrfs_root *root,
struct extent_buffer *buf,
struct extent_buffer *parent, int parent_slot,
struct extent_buffer **cow_ret,
u64 search_start, u64 empty_size,
u64 prealloc_dest)
u64 search_start, u64 empty_size)
{
u64 parent_start;
struct extent_buffer *cow;
Expand All @@ -291,26 +286,10 @@ static noinline int __btrfs_cow_block(struct btrfs_trans_handle *trans,
level = btrfs_header_level(buf);
nritems = btrfs_header_nritems(buf);

if (prealloc_dest) {
struct btrfs_key ins;

ins.objectid = prealloc_dest;
ins.offset = buf->len;
ins.type = BTRFS_EXTENT_ITEM_KEY;

ret = btrfs_alloc_reserved_extent(trans, root, parent_start,
root->root_key.objectid,
trans->transid, level, &ins);
BUG_ON(ret);
cow = btrfs_init_new_buffer(trans, root, prealloc_dest,
buf->len, level);
} else {
cow = btrfs_alloc_free_block(trans, root, buf->len,
parent_start,
root->root_key.objectid,
trans->transid, level,
search_start, empty_size);
}
cow = btrfs_alloc_free_block(trans, root, buf->len,
parent_start, root->root_key.objectid,
trans->transid, level,
search_start, empty_size);
if (IS_ERR(cow))
return PTR_ERR(cow);

Expand Down Expand Up @@ -413,7 +392,7 @@ static noinline int __btrfs_cow_block(struct btrfs_trans_handle *trans,
noinline int btrfs_cow_block(struct btrfs_trans_handle *trans,
struct btrfs_root *root, struct extent_buffer *buf,
struct extent_buffer *parent, int parent_slot,
struct extent_buffer **cow_ret, u64 prealloc_dest)
struct extent_buffer **cow_ret)
{
u64 search_start;
int ret;
Expand All @@ -436,7 +415,6 @@ noinline int btrfs_cow_block(struct btrfs_trans_handle *trans,
btrfs_header_owner(buf) == root->root_key.objectid &&
!btrfs_header_flag(buf, BTRFS_HEADER_FLAG_WRITTEN)) {
*cow_ret = buf;
WARN_ON(prealloc_dest);
return 0;
}

Expand All @@ -447,8 +425,7 @@ noinline int btrfs_cow_block(struct btrfs_trans_handle *trans,
btrfs_set_lock_blocking(buf);

ret = __btrfs_cow_block(trans, root, buf, parent,
parent_slot, cow_ret, search_start, 0,
prealloc_dest);
parent_slot, cow_ret, search_start, 0);
return ret;
}

Expand Down Expand Up @@ -617,7 +594,7 @@ int btrfs_realloc_node(struct btrfs_trans_handle *trans,
err = __btrfs_cow_block(trans, root, cur, parent, i,
&cur, search_start,
min(16 * blocksize,
(end_slot - i) * blocksize), 0);
(end_slot - i) * blocksize));
if (err) {
btrfs_tree_unlock(cur);
free_extent_buffer(cur);
Expand Down Expand Up @@ -937,7 +914,7 @@ static noinline int balance_level(struct btrfs_trans_handle *trans,
BUG_ON(!child);
btrfs_tree_lock(child);
btrfs_set_lock_blocking(child);
ret = btrfs_cow_block(trans, root, child, mid, 0, &child, 0);
ret = btrfs_cow_block(trans, root, child, mid, 0, &child);
BUG_ON(ret);

spin_lock(&root->node_lock);
Expand Down Expand Up @@ -979,7 +956,7 @@ static noinline int balance_level(struct btrfs_trans_handle *trans,
btrfs_tree_lock(left);
btrfs_set_lock_blocking(left);
wret = btrfs_cow_block(trans, root, left,
parent, pslot - 1, &left, 0);
parent, pslot - 1, &left);
if (wret) {
ret = wret;
goto enospc;
Expand All @@ -990,7 +967,7 @@ static noinline int balance_level(struct btrfs_trans_handle *trans,
btrfs_tree_lock(right);
btrfs_set_lock_blocking(right);
wret = btrfs_cow_block(trans, root, right,
parent, pslot + 1, &right, 0);
parent, pslot + 1, &right);
if (wret) {
ret = wret;
goto enospc;
Expand Down Expand Up @@ -1171,7 +1148,7 @@ static noinline int push_nodes_for_insert(struct btrfs_trans_handle *trans,
wret = 1;
} else {
ret = btrfs_cow_block(trans, root, left, parent,
pslot - 1, &left, 0);
pslot - 1, &left);
if (ret)
wret = 1;
else {
Expand Down Expand Up @@ -1222,7 +1199,7 @@ static noinline int push_nodes_for_insert(struct btrfs_trans_handle *trans,
} else {
ret = btrfs_cow_block(trans, root, right,
parent, pslot + 1,
&right, 0);
&right);
if (ret)
wret = 1;
else {
Expand Down Expand Up @@ -1492,7 +1469,6 @@ int btrfs_search_slot(struct btrfs_trans_handle *trans, struct btrfs_root
u8 lowest_level = 0;
u64 blocknr;
u64 gen;
struct btrfs_key prealloc_block;

lowest_level = p->lowest_level;
WARN_ON(lowest_level && ins_len > 0);
Expand All @@ -1501,8 +1477,6 @@ int btrfs_search_slot(struct btrfs_trans_handle *trans, struct btrfs_root
if (ins_len < 0)
lowest_unlock = 2;

prealloc_block.objectid = 0;

again:
if (p->skip_locking)
b = btrfs_root_node(root);
Expand All @@ -1529,44 +1503,11 @@ int btrfs_search_slot(struct btrfs_trans_handle *trans, struct btrfs_root
!btrfs_header_flag(b, BTRFS_HEADER_FLAG_WRITTEN)) {
goto cow_done;
}

/* ok, we have to cow, is our old prealloc the right
* size?
*/
if (prealloc_block.objectid &&
prealloc_block.offset != b->len) {
btrfs_release_path(root, p);
btrfs_free_reserved_extent(root,
prealloc_block.objectid,
prealloc_block.offset);
prealloc_block.objectid = 0;
goto again;
}

/*
* for higher level blocks, try not to allocate blocks
* with the block and the parent locks held.
*/
if (level > 0 && !prealloc_block.objectid) {
u32 size = b->len;
u64 hint = b->start;

btrfs_release_path(root, p);
ret = btrfs_reserve_extent(trans, root,
size, size, 0,
hint, (u64)-1,
&prealloc_block, 0);
BUG_ON(ret);
goto again;
}

btrfs_set_path_blocking(p);

wret = btrfs_cow_block(trans, root, b,
p->nodes[level + 1],
p->slots[level + 1],
&b, prealloc_block.objectid);
prealloc_block.objectid = 0;
p->slots[level + 1], &b);
if (wret) {
free_extent_buffer(b);
ret = wret;
Expand Down Expand Up @@ -1743,11 +1684,6 @@ int btrfs_search_slot(struct btrfs_trans_handle *trans, struct btrfs_root
* from here on, so for now just mark it as blocking
*/
btrfs_set_path_blocking(p);
if (prealloc_block.objectid) {
btrfs_free_reserved_extent(root,
prealloc_block.objectid,
prealloc_block.offset);
}
return ret;
}

Expand All @@ -1768,7 +1704,7 @@ int btrfs_merge_path(struct btrfs_trans_handle *trans,
int ret;

eb = btrfs_lock_root_node(root);
ret = btrfs_cow_block(trans, root, eb, NULL, 0, &eb, 0);
ret = btrfs_cow_block(trans, root, eb, NULL, 0, &eb);
BUG_ON(ret);

btrfs_set_lock_blocking(eb);
Expand Down Expand Up @@ -1826,7 +1762,7 @@ int btrfs_merge_path(struct btrfs_trans_handle *trans,
}

ret = btrfs_cow_block(trans, root, eb, parent, slot,
&eb, 0);
&eb);
BUG_ON(ret);

if (root->root_key.objectid ==
Expand Down Expand Up @@ -2377,7 +2313,7 @@ static int push_leaf_right(struct btrfs_trans_handle *trans, struct btrfs_root

/* cow and double check */
ret = btrfs_cow_block(trans, root, right, upper,
slot + 1, &right, 0);
slot + 1, &right);
if (ret)
goto out_unlock;

Expand Down Expand Up @@ -2576,7 +2512,7 @@ static int push_leaf_left(struct btrfs_trans_handle *trans, struct btrfs_root

/* cow and double check */
ret = btrfs_cow_block(trans, root, left,
path->nodes[1], slot - 1, &left, 0);
path->nodes[1], slot - 1, &left);
if (ret) {
/* we hit -ENOSPC, but it isn't fatal here */
ret = 1;
Expand Down
2 changes: 1 addition & 1 deletion fs/btrfs/ctree.h
View file
Original file line number Diff line number Diff line change
Expand Up @@ -1838,7 +1838,7 @@ int btrfs_search_forward(struct btrfs_root *root, struct btrfs_key *min_key,
int btrfs_cow_block(struct btrfs_trans_handle *trans,
struct btrfs_root *root, struct extent_buffer *buf,
struct extent_buffer *parent, int parent_slot,
struct extent_buffer **cow_ret, u64 prealloc_dest);
struct extent_buffer **cow_ret);
int btrfs_copy_root(struct btrfs_trans_handle *trans,
struct btrfs_root *root,
struct extent_buffer *buf,
Expand Down
4 changes: 2 additions & 2 deletions fs/btrfs/transaction.c
View file
Original file line number Diff line number Diff line change
Expand Up @@ -463,7 +463,7 @@ int btrfs_commit_tree_roots(struct btrfs_trans_handle *trans,
btrfs_extent_post_op(trans, fs_info->tree_root);

eb = btrfs_lock_root_node(fs_info->tree_root);
btrfs_cow_block(trans, fs_info->tree_root, eb, NULL, 0, &eb, 0);
btrfs_cow_block(trans, fs_info->tree_root, eb, NULL, 0, &eb);
btrfs_tree_unlock(eb);
free_extent_buffer(eb);

Expand Down Expand Up @@ -766,7 +766,7 @@ static noinline int create_pending_snapshot(struct btrfs_trans_handle *trans,
btrfs_set_key_type(&key, BTRFS_ROOT_ITEM_KEY);

old = btrfs_lock_root_node(root);
btrfs_cow_block(trans, root, old, NULL, 0, &old, 0);
btrfs_cow_block(trans, root, old, NULL, 0, &old);

btrfs_copy_root(trans, root, old, &tmp, objectid);
btrfs_tree_unlock(old);
Expand Down

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