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Btrfs: Add mount option to turn off data cow
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A number of workloads do not require copy on write data or checksumming.
mount -o nodatasum to disable checksums and -o nodatacow to disable
both copy on write and checksumming.

In nodatacow mode, copy on write is still performed when a given extent
is under snapshot.

Signed-off-by: Chris Mason <chris.mason@oracle.com>
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Chris Mason committed Sep 25, 2008
1 parent b6cda9b commit be20aa9
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Showing 5 changed files with 293 additions and 25 deletions.
53 changes: 52 additions & 1 deletion fs/btrfs/ctree.c
View file
Original file line number Diff line number Diff line change
Expand Up @@ -70,7 +70,58 @@ void btrfs_release_path(struct btrfs_root *root, struct btrfs_path *p)
memset(p, 0, sizeof(*p));
}

static int __btrfs_cow_block(struct btrfs_trans_handle *trans,
int btrfs_copy_root(struct btrfs_trans_handle *trans,
struct btrfs_root *root,
struct extent_buffer *buf,
struct extent_buffer **cow_ret, u64 new_root_objectid)
{
struct extent_buffer *cow;
u32 nritems;
int ret = 0;
int level;
struct btrfs_key first_key;
struct btrfs_root new_root;

memcpy(&new_root, root, sizeof(new_root));
new_root.root_key.objectid = new_root_objectid;

WARN_ON(root->ref_cows && trans->transid !=
root->fs_info->running_transaction->transid);
WARN_ON(root->ref_cows && trans->transid != root->last_trans);

level = btrfs_header_level(buf);
nritems = btrfs_header_nritems(buf);
if (nritems) {
if (level == 0)
btrfs_item_key_to_cpu(buf, &first_key, 0);
else
btrfs_node_key_to_cpu(buf, &first_key, 0);
} else {
first_key.objectid = 0;
}
cow = __btrfs_alloc_free_block(trans, &new_root, buf->len,
new_root_objectid,
trans->transid, first_key.objectid,
level, buf->start, 0);
if (IS_ERR(cow))
return PTR_ERR(cow);

copy_extent_buffer(cow, buf, 0, 0, cow->len);
btrfs_set_header_bytenr(cow, cow->start);
btrfs_set_header_generation(cow, trans->transid);
btrfs_set_header_owner(cow, new_root_objectid);

WARN_ON(btrfs_header_generation(buf) > trans->transid);
ret = btrfs_inc_ref(trans, &new_root, buf);
if (ret)
return ret;

btrfs_mark_buffer_dirty(cow);
*cow_ret = cow;
return 0;
}

int __btrfs_cow_block(struct btrfs_trans_handle *trans,
struct btrfs_root *root,
struct extent_buffer *buf,
struct extent_buffer *parent, int parent_slot,
Expand Down
8 changes: 8 additions & 0 deletions fs/btrfs/ctree.h
View file
Original file line number Diff line number Diff line change
Expand Up @@ -431,6 +431,7 @@ struct btrfs_root {
#define BTRFS_STRING_ITEM_KEY 253

#define BTRFS_MOUNT_NODATASUM 0x1
#define BTRFS_MOUNT_NODATACOW 0x2

#define btrfs_clear_opt(o, opt) ((o) &= ~BTRFS_MOUNT_##opt)
#define btrfs_set_opt(o, opt) ((o) |= BTRFS_MOUNT_##opt)
Expand Down Expand Up @@ -915,6 +916,9 @@ static inline u32 btrfs_level_size(struct btrfs_root *root, int level) {
btrfs_item_offset_nr(leaf, slot)))

/* extent-tree.c */
u32 btrfs_count_snapshots_in_path(struct btrfs_root *root,
struct btrfs_path *count_path,
u64 first_extent);
int btrfs_extent_post_op(struct btrfs_trans_handle *trans,
struct btrfs_root *root);
int btrfs_copy_pinned(struct btrfs_root *root, struct extent_map_tree *copy);
Expand Down Expand Up @@ -974,6 +978,10 @@ 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);
int btrfs_copy_root(struct btrfs_trans_handle *trans,
struct btrfs_root *root,
struct extent_buffer *buf,
struct extent_buffer **cow_ret, u64 new_root_objectid);
int btrfs_extend_item(struct btrfs_trans_handle *trans, struct btrfs_root
*root, struct btrfs_path *path, u32 data_size);
int btrfs_truncate_item(struct btrfs_trans_handle *trans,
Expand Down
101 changes: 98 additions & 3 deletions fs/btrfs/extent-tree.c
View file
Original file line number Diff line number Diff line change
Expand Up @@ -679,6 +679,104 @@ static int lookup_extent_ref(struct btrfs_trans_handle *trans,
return 0;
}

u32 btrfs_count_snapshots_in_path(struct btrfs_root *root,
struct btrfs_path *count_path,
u64 first_extent)
{
struct btrfs_root *extent_root = root->fs_info->extent_root;
struct btrfs_path *path;
u64 bytenr;
u64 found_objectid;
u64 root_objectid = 0;
u32 total_count = 0;
u32 cur_count;
u32 refs;
u32 nritems;
int ret;
struct btrfs_key key;
struct btrfs_key found_key;
struct extent_buffer *l;
struct btrfs_extent_item *item;
struct btrfs_extent_ref *ref_item;
int level = -1;

path = btrfs_alloc_path();
again:
if (level == -1)
bytenr = first_extent;
else
bytenr = count_path->nodes[level]->start;

cur_count = 0;
key.objectid = bytenr;
key.offset = 0;

btrfs_set_key_type(&key, BTRFS_EXTENT_ITEM_KEY);
ret = btrfs_search_slot(NULL, extent_root, &key, path, 0, 0);
if (ret < 0)
goto out;
BUG_ON(ret == 0);

l = path->nodes[0];
btrfs_item_key_to_cpu(l, &found_key, path->slots[0]);

if (found_key.objectid != bytenr ||
found_key.type != BTRFS_EXTENT_ITEM_KEY) {
goto out;
}

item = btrfs_item_ptr(l, path->slots[0], struct btrfs_extent_item);
refs = btrfs_extent_refs(l, item);
while (1) {
nritems = btrfs_header_nritems(l);
if (path->slots[0] >= nritems) {
ret = btrfs_next_leaf(extent_root, path);
if (ret == 0)
continue;
break;
}
btrfs_item_key_to_cpu(l, &found_key, path->slots[0]);
if (found_key.objectid != bytenr)
break;
if (found_key.type != BTRFS_EXTENT_REF_KEY) {
path->slots[0]++;
continue;
}

cur_count++;
ref_item = btrfs_item_ptr(l, path->slots[0],
struct btrfs_extent_ref);
found_objectid = btrfs_ref_root(l, ref_item);

if (found_objectid != root_objectid)
total_count++;

if (total_count > 1)
goto out;

if (root_objectid == 0)
root_objectid = found_objectid;

path->slots[0]++;
}
if (cur_count == 0) {
total_count = 0;
goto out;
}
if (total_count > 1)
goto out;
if (level >= 0 && root->node == count_path->nodes[level])
goto out;
level++;
btrfs_release_path(root, path);
goto again;

out:
btrfs_free_path(path);
return total_count;

}

int btrfs_inc_root_ref(struct btrfs_trans_handle *trans,
struct btrfs_root *root, u64 owner_objectid)
{
Expand Down Expand Up @@ -1127,9 +1225,6 @@ static int __free_extent(struct btrfs_trans_handle *trans, struct btrfs_root
if (!path)
return -ENOMEM;

if (ref_generation && owner_objectid == 0 && root_objectid == 3) {
//printk("drop backref root %Lu gen %Lu byte %Lu\n", root_objectid, ref_generation, bytenr );
}
ret = lookup_extent_backref(trans, extent_root, path,
bytenr, root_objectid,
ref_generation,
Expand Down
122 changes: 108 additions & 14 deletions fs/btrfs/inode.c
View file
Original file line number Diff line number Diff line change
Expand Up @@ -72,21 +72,22 @@ static unsigned char btrfs_type_by_mode[S_IFMT >> S_SHIFT] = {
[S_IFLNK >> S_SHIFT] = BTRFS_FT_SYMLINK,
};

static int run_delalloc_range(struct inode *inode, u64 start, u64 end)
static int cow_file_range(struct inode *inode, u64 start, u64 end)
{
struct btrfs_root *root = BTRFS_I(inode)->root;
struct btrfs_trans_handle *trans;
struct btrfs_key ins;
u64 alloc_hint = 0;
u64 num_bytes;
int ret;
u64 blocksize = root->sectorsize;
struct btrfs_key ins;
int ret;

mutex_lock(&root->fs_info->fs_mutex);
trans = btrfs_start_transaction(root, 1);
btrfs_set_trans_block_group(trans, inode);
BUG_ON(!trans);
btrfs_set_trans_block_group(trans, inode);

num_bytes = (end - start + blocksize) & ~(blocksize - 1);
num_bytes = max(blocksize, num_bytes);
ret = btrfs_drop_extents(trans, root, inode,
start, start + num_bytes, start, &alloc_hint);

Expand All @@ -106,6 +107,101 @@ static int run_delalloc_range(struct inode *inode, u64 start, u64 end)
ins.offset);
out:
btrfs_end_transaction(trans, root);
return ret;
}

static int run_delalloc_nocow(struct inode *inode, u64 start, u64 end)
{
u64 extent_start;
u64 extent_end;
u64 bytenr;
u64 cow_end;
struct btrfs_root *root = BTRFS_I(inode)->root;
struct extent_buffer *leaf;
int found_type;
struct btrfs_path *path;
struct btrfs_file_extent_item *item;
int ret;
int err;
struct btrfs_key found_key;

path = btrfs_alloc_path();
BUG_ON(!path);
again:
ret = btrfs_lookup_file_extent(NULL, root, path,
inode->i_ino, start, 0);
if (ret < 0) {
btrfs_free_path(path);
return ret;
}

cow_end = end;
if (ret != 0) {
if (path->slots[0] == 0)
goto not_found;
path->slots[0]--;
}

leaf = path->nodes[0];
item = btrfs_item_ptr(leaf, path->slots[0],
struct btrfs_file_extent_item);

/* are we inside the extent that was found? */
btrfs_item_key_to_cpu(leaf, &found_key, path->slots[0]);
found_type = btrfs_key_type(&found_key);
if (found_key.objectid != inode->i_ino ||
found_type != BTRFS_EXTENT_DATA_KEY) {
goto not_found;
}

found_type = btrfs_file_extent_type(leaf, item);
extent_start = found_key.offset;
if (found_type == BTRFS_FILE_EXTENT_REG) {
extent_end = extent_start +
btrfs_file_extent_num_bytes(leaf, item);
err = 0;

if (start < extent_start || start >= extent_end)
goto not_found;

cow_end = min(end, extent_end - 1);
bytenr = btrfs_file_extent_disk_bytenr(leaf, item);
if (bytenr == 0)
goto not_found;

bytenr += btrfs_file_extent_offset(leaf, item);
if (btrfs_count_snapshots_in_path(root, path, bytenr) != 1) {
goto not_found;
}

start = extent_end;
} else if (found_type == BTRFS_FILE_EXTENT_INLINE) {
goto not_found;
}
loop:
if (start > end) {
btrfs_free_path(path);
return 0;
}
btrfs_release_path(root, path);
goto again;

not_found:
cow_file_range(inode, start, cow_end);
start = cow_end + 1;
goto loop;
}

static int run_delalloc_range(struct inode *inode, u64 start, u64 end)
{
struct btrfs_root *root = BTRFS_I(inode)->root;
int ret;

mutex_lock(&root->fs_info->fs_mutex);
if (btrfs_test_opt(root, NODATACOW))
ret = run_delalloc_nocow(inode, start, end);
else
ret = cow_file_range(inode, start, end);
mutex_unlock(&root->fs_info->fs_mutex);
return ret;
}
Expand Down Expand Up @@ -1907,9 +2003,6 @@ int btrfs_commit_write(struct file *file, struct page *page,

btrfs_cow_one_page(inode, page, PAGE_CACHE_SIZE);

set_page_extent_mapped(page);
set_page_dirty(page);

if (pos > inode->i_size) {
i_size_write(inode, pos);
mark_inode_dirty(inode);
Expand Down Expand Up @@ -2078,13 +2171,18 @@ static int create_snapshot(struct btrfs_root *root, char *name, int namelen)
key.objectid = objectid;
key.offset = 1;
btrfs_set_key_type(&key, BTRFS_ROOT_ITEM_KEY);

extent_buffer_get(root->node);
btrfs_cow_block(trans, root, root->node, NULL, 0, &tmp);
free_extent_buffer(tmp);
btrfs_set_root_bytenr(&new_root_item, root->node->start);
btrfs_set_root_level(&new_root_item, btrfs_header_level(root->node));

btrfs_copy_root(trans, root, root->node, &tmp, objectid);

btrfs_set_root_bytenr(&new_root_item, tmp->start);
btrfs_set_root_level(&new_root_item, btrfs_header_level(tmp));
ret = btrfs_insert_root(trans, root->fs_info->tree_root, &key,
&new_root_item);
free_extent_buffer(tmp);
if (ret)
goto fail;

Expand All @@ -2106,10 +2204,6 @@ static int create_snapshot(struct btrfs_root *root, char *name, int namelen)

if (ret)
goto fail;

ret = btrfs_inc_root_ref(trans, root, objectid);
if (ret)
goto fail;
fail:
nr = trans->blocks_used;
err = btrfs_commit_transaction(trans, root);
Expand Down
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