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Btrfs: don't read leaf blocks containing only checksums during truncate

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Checksum items take up a significant portion of the metadata for large files.
It is possible to avoid reading them during truncates by checking the keys in
the higher level nodes.

If a given leaf is followed by another leaf where the lowest key is a checksum
item from the same file, we know we can safely delete the leaf without
reading it.

For a 32GB file on a 6 drive raid0 array, Btrfs needs 8s to delete
the file with a cold cache.  It is read bound during the run.

With this change, Btrfs is able to delete the file in 0.5s

Signed-off-by: Chris Mason <chris.mason@oracle.com>
This commit is contained in:
Chris Mason
2008-10-01 19:05:46 -04:00
parent cf74982385
commit 323ac95bce
3 changed files with 193 additions and 32 deletions
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69
fs/btrfs/ctree.c
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@ -1388,7 +1388,7 @@ int btrfs_search_slot(struct btrfs_trans_handle *trans, struct btrfs_root
struct btrfs_key prealloc_block;
lowest_level = p->lowest_level;
WARN_ON(lowest_level && ins_len);
WARN_ON(lowest_level && ins_len > 0);
WARN_ON(p->nodes[0] != NULL);
WARN_ON(cow && root == root->fs_info->extent_root &&
!mutex_is_locked(&root->fs_info->alloc_mutex));
@ -3186,6 +3186,36 @@ static int del_ptr(struct btrfs_trans_handle *trans, struct btrfs_root *root,
return ret;
}
/*
* a helper function to delete the leaf pointed to by path->slots[1] and
* path->nodes[1]. bytenr is the node block pointer, but since the callers
* already know it, it is faster to have them pass it down than to
* read it out of the node again.
*
* This deletes the pointer in path->nodes[1] and frees the leaf
* block extent. zero is returned if it all worked out, < 0 otherwise.
*
* The path must have already been setup for deleting the leaf, including
* all the proper balancing. path->nodes[1] must be locked.
*/
noinline int btrfs_del_leaf(struct btrfs_trans_handle *trans,
struct btrfs_root *root,
struct btrfs_path *path, u64 bytenr)
{
int ret;
u64 root_gen = btrfs_header_generation(path->nodes[1]);
ret = del_ptr(trans, root, path, 1, path->slots[1]);
if (ret)
return ret;
ret = btrfs_free_extent(trans, root, bytenr,
btrfs_level_size(root, 0),
path->nodes[1]->start,
btrfs_header_owner(path->nodes[1]),
root_gen, 0, 0, 1);
return ret;
}
/*
* delete the item at the leaf level in path. If that empties
* the leaf, remove it from the tree
@ -3251,17 +3281,8 @@ int btrfs_del_items(struct btrfs_trans_handle *trans, struct btrfs_root *root,
if (leaf == root->node) {
btrfs_set_header_level(leaf, 0);
} else {
u64 root_gen = btrfs_header_generation(path->nodes[1]);
wret = del_ptr(trans, root, path, 1, path->slots[1]);
if (wret)
ret = wret;
wret = btrfs_free_extent(trans, root,
leaf->start, leaf->len,
path->nodes[1]->start,
btrfs_header_owner(path->nodes[1]),
root_gen, 0, 0, 1);
if (wret)
ret = wret;
ret = btrfs_del_leaf(trans, root, path, leaf->start);
BUG_ON(ret);
}
} else {
int used = leaf_space_used(leaf, 0, nritems);
@ -3296,24 +3317,10 @@ int btrfs_del_items(struct btrfs_trans_handle *trans, struct btrfs_root *root,
}
if (btrfs_header_nritems(leaf) == 0) {
u64 root_gen;
u64 bytenr = leaf->start;
u32 blocksize = leaf->len;
root_gen = btrfs_header_generation(
path->nodes[1]);
wret = del_ptr(trans, root, path, 1, slot);
if (wret)
ret = wret;
path->slots[1] = slot;
ret = btrfs_del_leaf(trans, root, path, leaf->start);
BUG_ON(ret);
free_extent_buffer(leaf);
wret = btrfs_free_extent(trans, root, bytenr,
blocksize, path->nodes[1]->start,
btrfs_header_owner(path->nodes[1]),
root_gen, 0, 0, 1);
if (wret)
ret = wret;
} else {
/* if we're still in the path, make sure
* we're dirty. Otherwise, one of the
@ -3418,8 +3425,8 @@ again:
level = btrfs_header_level(cur);
sret = bin_search(cur, min_key, level, &slot);
/* at level = 0, we're done, setup the path and exit */
if (level == 0) {
/* at the lowest level, we're done, setup the path and exit */
if (level == path->lowest_level) {
if (slot >= nritems)
goto find_next_key;
ret = 0;