Josef Bacik
2011-Apr-06 18:56 UTC
[PATCH] Btrfs: reuse the extent_map we found when calling btrfs_get_extent
In btrfs_get_block_direct we call btrfs_get_extent to lookup the extent for the
range that we are looking for. If we don''t find an extent,
btrfs_get_extent
will insert a extent_map for that area and mark it as a hole. So it does the
job of allocating a new extent map and inserting it into the io tree. But if
we''re creating a new extent we free it up and redo all of that work.
So instead
pass the em to btrfs_new_extent_direct(), and if it will work just allocate the
disk space and set it up properly and bypass the freeing/allocating of a new
extent map and the expensive operation of inserting the thing into the io_tree.
Thanks,
Signed-off-by: Josef Bacik <josef@redhat.com>
---
fs/btrfs/inode.c | 36 ++++++++++++++++++++++++++++--------
1 files changed, 28 insertions(+), 8 deletions(-)
diff --git a/fs/btrfs/inode.c b/fs/btrfs/inode.c
index 93ed346..032e8fb 100644
--- a/fs/btrfs/inode.c
+++ b/fs/btrfs/inode.c
@@ -5443,17 +5443,30 @@ out:
}
static struct extent_map *btrfs_new_extent_direct(struct inode *inode,
+ struct extent_map *em,
u64 start, u64 len)
{
struct btrfs_root *root = BTRFS_I(inode)->root;
struct btrfs_trans_handle *trans;
- struct extent_map *em;
struct extent_map_tree *em_tree = &BTRFS_I(inode)->extent_tree;
struct btrfs_key ins;
u64 alloc_hint;
int ret;
+ bool insert = false;
- btrfs_drop_extent_cache(inode, start, start + len - 1, 0);
+ /*
+ * Ok if the extent map we looked up is a hole and is for the exact
+ * range we want, there is no reason to allocate a new one, however if
+ * it is not right then we need to free this one and drop the cache for
+ * our range.
+ */
+ if (em->block_start != EXTENT_MAP_HOLE || em->start != start ||
+ em->len != len) {
+ free_extent_map(em);
+ em = NULL;
+ insert = true;
+ btrfs_drop_extent_cache(inode, start, start + len - 1, 0);
+ }
trans = btrfs_join_transaction(root, 0);
if (IS_ERR(trans))
@@ -5469,10 +5482,12 @@ static struct extent_map *btrfs_new_extent_direct(struct
inode *inode,
goto out;
}
- em = alloc_extent_map(GFP_NOFS);
if (!em) {
- em = ERR_PTR(-ENOMEM);
- goto out;
+ em = alloc_extent_map(GFP_NOFS);
+ if (!em) {
+ em = ERR_PTR(-ENOMEM);
+ goto out;
+ }
}
em->start = start;
@@ -5482,9 +5497,15 @@ static struct extent_map *btrfs_new_extent_direct(struct
inode *inode,
em->block_start = ins.objectid;
em->block_len = ins.offset;
em->bdev = root->fs_info->fs_devices->latest_bdev;
+
+ /*
+ * We need to do this because if we''re using the original em we
searched
+ * for, we could have EXTENT_FLAG_VACANCY set, and we don''t want
that.
+ */
+ em->flags = 0;
set_bit(EXTENT_FLAG_PINNED, &em->flags);
- while (1) {
+ while (insert) {
write_lock(&em_tree->lock);
ret = add_extent_mapping(em_tree, em);
write_unlock(&em_tree->lock);
@@ -5702,8 +5723,7 @@ must_cow:
* it above
*/
len = bh_result->b_size;
- free_extent_map(em);
- em = btrfs_new_extent_direct(inode, start, len);
+ em = btrfs_new_extent_direct(inode, em, start, len);
if (IS_ERR(em))
return PTR_ERR(em);
len = min(len, em->len - (start - em->start));
--
1.7.2.3
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