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Btrfs: optimize leaf_space_used 

This gets called at least 4 times for every level while adding an object,
and it involves 3 kmapping calls, which on my box take about 5us a piece.
So instead use a token, which brings us down to 1 kmap call and makes this
function take 1/3 of the time per call.  Thanks,

Signed-off-by: Josef Bacik <jbacik@fusionio.com>
Signed-off-by: Chris Mason <chris.mason@fusionio.com>
This commit is contained in:
Josef Bacik 2012-10-15 13:43:18 -04:00 committed by Chris Mason
parent ad91455969
commit 41be1f3b40
1 changed files with 9 additions and 2 deletions
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11
fs/btrfs/ctree.c
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@ -3298,14 +3298,21 @@ static noinline int split_node(struct btrfs_trans_handle *trans,
*/
static int leaf_space_used(struct extent_buffer *l, int start, int nr)
{
struct btrfs_item *start_item;
struct btrfs_item *end_item;
struct btrfs_map_token token;
int data_len;
int nritems = btrfs_header_nritems(l);
int end = min(nritems, start + nr) - 1;
if (!nr)
return 0;
data_len = btrfs_item_end_nr(l, start);
data_len = data_len - btrfs_item_offset_nr(l, end);
btrfs_init_map_token(&token);
start_item = btrfs_item_nr(l, start);
end_item = btrfs_item_nr(l, end);
data_len = btrfs_token_item_offset(l, start_item, &token) +
btrfs_token_item_size(l, start_item, &token);
data_len = data_len - btrfs_token_item_offset(l, end_item, &token);
data_len += sizeof(struct btrfs_item) * nr;
WARN_ON(data_len < 0);
return data_len;