I need everybody to go over this with a fine toothed comb since it is a pretty
big change. I think it is right and it seems to come out right, but if it's not
it will mean we screw up O_DIRECT on snapshotted files with preallocated
extents, so please, make sure it is correct :).
---
Subject: [PATCH] Btrfs: rework can_nocow_odirect
We are always doing the file extent lookup in here even though we've already
done the btrfs_get_extent which does the exact same thing. So re-work
can_nocow_odirect to get the same information out of the extent_map we
already have and then do the cross ref check and csum checks as appropriate.
This reduces the number of allocations and searches we do for every O_DIRECT
write and man it helps a lot. Thanks,
Signed-off-by: Josef Bacik <jba...@fusionio.com>
---
fs/btrfs/inode.c | 93 ++++++++++++++---------------------------------------
1 files changed, 25 insertions(+), 68 deletions(-)
diff --git a/fs/btrfs/inode.c b/fs/btrfs/inode.c
index 2c785c0..1cd7a6b 100644
--- a/fs/btrfs/inode.c
+++ b/fs/btrfs/inode.c
@@ -6352,79 +6352,42 @@ out:
* block must be cow'd
*/
static noinline int can_nocow_odirect(struct btrfs_trans_handle *trans,
- struct inode *inode, u64 offset, u64 len)
+ struct inode *inode,
+ struct extent_map *em, u64 offset,
+ u64 len)
{
- struct btrfs_path *path;
- int ret;
- struct extent_buffer *leaf;
struct btrfs_root *root = BTRFS_I(inode)->root;
- struct btrfs_file_extent_item *fi;
- struct btrfs_key key;
u64 disk_bytenr;
u64 backref_offset;
u64 extent_end;
u64 num_bytes;
- int slot;
- int found_type;
-
- path = btrfs_alloc_path();
- if (!path)
- return -ENOMEM;
-
- ret = btrfs_lookup_file_extent(trans, root, path, btrfs_ino(inode),
- offset, 0);
- if (ret < 0)
- goto out;
- slot = path->slots[0];
- if (ret == 1) {
- if (slot == 0) {
- /* can't find the item, must cow */
- ret = 0;
- goto out;
- }
- slot--;
- }
- ret = 0;
- leaf = path->nodes[0];
- btrfs_item_key_to_cpu(leaf, &key, slot);
- if (key.objectid != btrfs_ino(inode) ||
- key.type != BTRFS_EXTENT_DATA_KEY) {
- /* not our file or wrong item type, must cow */
- goto out;
- }
-
- if (key.offset > offset) {
- /* Wrong offset, must cow */
- goto out;
- }
-
- fi = btrfs_item_ptr(leaf, slot, struct btrfs_file_extent_item);
- found_type = btrfs_file_extent_type(leaf, fi);
- if (found_type != BTRFS_FILE_EXTENT_REG &&
- found_type != BTRFS_FILE_EXTENT_PREALLOC) {
- /* not a regular extent, must cow */
- goto out;
- }
- disk_bytenr = btrfs_file_extent_disk_bytenr(leaf, fi);
- backref_offset = btrfs_file_extent_offset(leaf, fi);
+ if (em->block_start == EXTENT_MAP_INLINE ||
+ em->block_start == EXTENT_MAP_HOLE)
+ return 0;
- extent_end = key.offset + btrfs_file_extent_num_bytes(leaf, fi);
- if (extent_end < offset + len) {
- /* extent doesn't include our full range, must cow */
- goto out;
- }
+ /*
+ * The em's disk_bytenr is already adjusted for its offset so we need to
+ * adjust it accordingly.
+ */
+ backref_offset = em->start - em->orig_start;
+ disk_bytenr = em->block_start - backref_offset;
+ extent_end = em->start + em->len;
if (btrfs_extent_readonly(root, disk_bytenr))
- goto out;
+ return 0;
/*
* look for other files referencing this extent, if we
* find any we must cow
*/
if (btrfs_cross_ref_exist(trans, root, btrfs_ino(inode),
- key.offset - backref_offset, disk_bytenr))
- goto out;
+ em->orig_start, disk_bytenr))
+ return 0;
+
+ /* No prealloc, we won't have csums */
+ if (test_bit(EXTENT_FLAG_PREALLOC, &em->flags))
+ return 1;
/*
* adjust disk_bytenr and num_bytes to cover just the bytes
@@ -6433,18 +6396,12 @@ static noinline int can_nocow_odirect(struct
btrfs_trans_handle *trans,
* to keep the csums correct
*/
disk_bytenr += backref_offset;
- disk_bytenr += offset - key.offset;
+ disk_bytenr += offset - em->start;
num_bytes = min(offset + len, extent_end) - offset;
if (csum_exist_in_range(root, disk_bytenr, num_bytes))
- goto out;
- /*
- * all of the above have passed, it is safe to overwrite this extent
- * without cow
- */
- ret = 1;
-out:
- btrfs_free_path(path);
- return ret;
+ return 0;
+
+ return 1;
}
static int lock_extent_direct(struct inode *inode, u64 lockstart, u64 lockend,
@@ -6663,7 +6620,7 @@ static int btrfs_get_blocks_direct(struct inode *inode,
sector_t iblock,
if (IS_ERR(trans))
goto must_cow;
- if (can_nocow_odirect(trans, inode, start, len) == 1) {
+ if (can_nocow_odirect(trans, inode, em, start, len) == 1) {
u64 orig_start = em->start;
if (type == BTRFS_ORDERED_PREALLOC) {
--
1.7.7.6
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