* [PATCH 1/2] btrfs: move common NOCOW checks against a file extent into a helper
2022-03-30 14:31 [PATCH 0/2] btrfs: some refactor and cleanup for NOCOW write paths fdmanana
@ 2022-03-30 14:31 ` fdmanana
2022-03-30 14:31 ` [PATCH 2/2] btrfs: do not test for free space inode during NOCOW check against file extent fdmanana
2022-03-31 18:14 ` [PATCH 0/2] btrfs: some refactor and cleanup for NOCOW write paths David Sterba
2 siblings, 0 replies; 4+ messages in thread
From: fdmanana @ 2022-03-30 14:31 UTC (permalink / raw)
To: linux-btrfs
From: Filipe Manana <fdmanana@suse.com>
Verifying if we can do a NOCOW write against a range fully or partially
covered by a file extent item requires verifying several constraints, and
these are currently duplicated at two different places: can_nocow_extent()
and run_delalloc_nocow().
This change moves those checks into a common helper function to avoid
duplication. It adds some comments and also preserves all existing
behaviour like for example can_nocow_extent() treating errors from the
calls to btrfs_cross_ref_exist() and csum_exist_in_range() as meaning
we can not NOCOW, instead of propagating the error back to the caller.
That specific behaviour is questionable but also reasonable to some
degree.
Signed-off-by: Filipe Manana <fdmanana@suse.com>
---
fs/btrfs/inode.c | 428 ++++++++++++++++++++++++-----------------------
1 file changed, 216 insertions(+), 212 deletions(-)
diff --git a/fs/btrfs/inode.c b/fs/btrfs/inode.c
index faf76da2526f..ae63e6a85cac 100644
--- a/fs/btrfs/inode.c
+++ b/fs/btrfs/inode.c
@@ -1629,6 +1629,142 @@ static int fallback_to_cow(struct btrfs_inode *inode, struct page *locked_page,
nr_written, 1);
}
+struct can_nocow_file_extent_args {
+ /* Input fields. */
+
+ /* Start file offset of the range we want to NOCOW. */
+ u64 start;
+ /* End file offset (inclusive) of the range we want to NOCOW. */
+ u64 end;
+ bool writeback_path;
+ bool strict;
+ /*
+ * Free the path passed to can_nocow_file_extent() once it's not needed
+ * anymore.
+ */
+ bool free_path;
+
+ /* Output fields. Only set when can_nocow_file_extent() returns 1. */
+
+ u64 disk_bytenr;
+ u64 disk_num_bytes;
+ u64 extent_offset;
+ /* Number of bytes that can be written to in NOCOW mode. */
+ u64 num_bytes;
+};
+
+/*
+ * Check if we can NOCOW the file extent that the path points to.
+ * This function may return with the path released, so the caller should check
+ * if path->nodes[0] is NULL or not if it needs to use the path afterwards.
+ *
+ * Returns: < 0 on error
+ * 0 if we can not NOCOW
+ * 1 if we can NOCOW
+ */
+static int can_nocow_file_extent(struct btrfs_path *path,
+ struct btrfs_key *key,
+ struct btrfs_inode *inode,
+ struct can_nocow_file_extent_args *args)
+{
+ const bool is_freespace_inode = btrfs_is_free_space_inode(inode);
+ struct extent_buffer *leaf = path->nodes[0];
+ struct btrfs_root *root = inode->root;
+ struct btrfs_file_extent_item *fi;
+ u64 extent_end;
+ u8 extent_type;
+ int can_nocow = 0;
+ int ret = 0;
+
+ fi = btrfs_item_ptr(leaf, path->slots[0], struct btrfs_file_extent_item);
+ extent_type = btrfs_file_extent_type(leaf, fi);
+
+ if (extent_type == BTRFS_FILE_EXTENT_INLINE)
+ goto out;
+
+ /* Can't access these fields unless we know it's not an inline extent. */
+ args->disk_bytenr = btrfs_file_extent_disk_bytenr(leaf, fi);
+ args->disk_num_bytes = btrfs_file_extent_disk_num_bytes(leaf, fi);
+ args->extent_offset = btrfs_file_extent_offset(leaf, fi);
+
+ if (!(inode->flags & BTRFS_INODE_NODATACOW) &&
+ extent_type == BTRFS_FILE_EXTENT_REG)
+ goto out;
+
+ /*
+ * If the extent was created before the generation where the last snapshot
+ * for its subvolume was created, then this implies the extent is shared,
+ * hence we must COW.
+ */
+ if (!args->strict && !is_freespace_inode &&
+ btrfs_file_extent_generation(leaf, fi) <=
+ btrfs_root_last_snapshot(&root->root_item))
+ goto out;
+
+ /* An explicit hole, must COW. */
+ if (args->disk_bytenr == 0)
+ goto out;
+
+ /* Compressed/encrypted/encoded extents must be COWed. */
+ if (btrfs_file_extent_compression(leaf, fi) ||
+ btrfs_file_extent_encryption(leaf, fi) ||
+ btrfs_file_extent_other_encoding(leaf, fi))
+ goto out;
+
+ extent_end = btrfs_file_extent_end(path);
+
+ /*
+ * The following checks can be expensive, as they need to take other
+ * locks and do btree or rbtree searches, so release the path to avoid
+ * blocking other tasks for too long.
+ */
+ btrfs_release_path(path);
+
+ ret = btrfs_cross_ref_exist(root, btrfs_ino(inode),
+ key->offset - args->extent_offset,
+ args->disk_bytenr, false, path);
+ WARN_ON_ONCE(ret > 0 && is_freespace_inode);
+ if (ret != 0)
+ goto out;
+
+ if (args->free_path) {
+ /*
+ * We don't need the path anymore, plus through the
+ * csum_exist_in_range() call below we will end up allocating
+ * another path. So free the path to avoid unnecessary extra
+ * memory usage.
+ */
+ btrfs_free_path(path);
+ path = NULL;
+ }
+
+ /* If there are pending snapshots for this root, we must COW. */
+ if (args->writeback_path && !is_freespace_inode &&
+ atomic_read(&root->snapshot_force_cow))
+ goto out;
+
+ args->disk_bytenr += args->extent_offset;
+ args->disk_bytenr += args->start - key->offset;
+ args->num_bytes = min(args->end + 1, extent_end) - args->start;
+
+ /*
+ * Force cow if csums exist in the range. This ensures that csums for a
+ * given extent are either valid or do not exist.
+ */
+ ret = csum_exist_in_range(root->fs_info, args->disk_bytenr,
+ args->num_bytes);
+ WARN_ON_ONCE(ret > 0 && is_freespace_inode);
+ if (ret != 0)
+ goto out;
+
+ can_nocow = 1;
+ out:
+ if (args->free_path && path)
+ btrfs_free_path(path);
+
+ return ret < 0 ? ret : can_nocow;
+}
+
/*
* when nowcow writeback call back. This checks for snapshots or COW copies
* of the extents that exist in the file, and COWs the file as required.
@@ -1649,11 +1785,9 @@ static noinline int run_delalloc_nocow(struct btrfs_inode *inode,
u64 cur_offset = start;
int ret;
bool check_prev = true;
- const bool freespace_inode = btrfs_is_free_space_inode(inode);
u64 ino = btrfs_ino(inode);
bool nocow = false;
- u64 disk_bytenr = 0;
- const bool force = inode->flags & BTRFS_INODE_NODATACOW;
+ struct can_nocow_file_extent_args nocow_args = { 0 };
path = btrfs_alloc_path();
if (!path) {
@@ -1666,15 +1800,16 @@ static noinline int run_delalloc_nocow(struct btrfs_inode *inode,
return -ENOMEM;
}
+ nocow_args.end = end;
+ nocow_args.writeback_path = true;
+
while (1) {
struct btrfs_key found_key;
struct btrfs_file_extent_item *fi;
struct extent_buffer *leaf;
u64 extent_end;
- u64 extent_offset;
- u64 num_bytes = 0;
- u64 disk_num_bytes;
u64 ram_bytes;
+ u64 nocow_end;
int extent_type;
nocow = false;
@@ -1750,117 +1885,37 @@ static noinline int run_delalloc_nocow(struct btrfs_inode *inode,
fi = btrfs_item_ptr(leaf, path->slots[0],
struct btrfs_file_extent_item);
extent_type = btrfs_file_extent_type(leaf, fi);
-
+ /* If this is triggered then we have a memory corruption. */
+ ASSERT(extent_type < BTRFS_NR_FILE_EXTENT_TYPES);
+ if (WARN_ON(extent_type >= BTRFS_NR_FILE_EXTENT_TYPES)) {
+ ret = -EUCLEAN;
+ goto error;
+ }
ram_bytes = btrfs_file_extent_ram_bytes(leaf, fi);
- if (extent_type == BTRFS_FILE_EXTENT_REG ||
- extent_type == BTRFS_FILE_EXTENT_PREALLOC) {
- disk_bytenr = btrfs_file_extent_disk_bytenr(leaf, fi);
- extent_offset = btrfs_file_extent_offset(leaf, fi);
- extent_end = found_key.offset +
- btrfs_file_extent_num_bytes(leaf, fi);
- disk_num_bytes =
- btrfs_file_extent_disk_num_bytes(leaf, fi);
- /*
- * If the extent we got ends before our current offset,
- * skip to the next extent.
- */
- if (extent_end <= cur_offset) {
- path->slots[0]++;
- goto next_slot;
- }
- /* Skip holes */
- if (disk_bytenr == 0)
- goto out_check;
- /* Skip compressed/encrypted/encoded extents */
- if (btrfs_file_extent_compression(leaf, fi) ||
- btrfs_file_extent_encryption(leaf, fi) ||
- btrfs_file_extent_other_encoding(leaf, fi))
- goto out_check;
- /*
- * If extent is created before the last volume's snapshot
- * this implies the extent is shared, hence we can't do
- * nocow. This is the same check as in
- * btrfs_cross_ref_exist but without calling
- * btrfs_search_slot.
- */
- if (!freespace_inode &&
- btrfs_file_extent_generation(leaf, fi) <=
- btrfs_root_last_snapshot(&root->root_item))
- goto out_check;
- if (extent_type == BTRFS_FILE_EXTENT_REG && !force)
- goto out_check;
+ extent_end = btrfs_file_extent_end(path);
- /*
- * The following checks can be expensive, as they need to
- * take other locks and do btree or rbtree searches, so
- * release the path to avoid blocking other tasks for too
- * long.
- */
- btrfs_release_path(path);
+ /*
+ * If the extent we got ends before our current offset, skip to
+ * the next extent.
+ */
+ if (extent_end <= cur_offset) {
+ path->slots[0]++;
+ goto next_slot;
+ }
- ret = btrfs_cross_ref_exist(root, ino,
- found_key.offset -
- extent_offset, disk_bytenr,
- false, path);
- if (ret) {
- /*
- * ret could be -EIO if the above fails to read
- * metadata.
- */
- if (ret < 0) {
- if (cow_start != (u64)-1)
- cur_offset = cow_start;
- goto error;
- }
+ nocow_args.start = cur_offset;
+ ret = can_nocow_file_extent(path, &found_key, inode, &nocow_args);
+ if (ret < 0) {
+ if (cow_start != (u64)-1)
+ cur_offset = cow_start;
+ goto error;
+ } else if (ret == 0) {
+ goto out_check;
+ }
- WARN_ON_ONCE(freespace_inode);
- goto out_check;
- }
- disk_bytenr += extent_offset;
- disk_bytenr += cur_offset - found_key.offset;
- num_bytes = min(end + 1, extent_end) - cur_offset;
- /*
- * If there are pending snapshots for this root, we
- * fall into common COW way
- */
- if (!freespace_inode && atomic_read(&root->snapshot_force_cow))
- goto out_check;
- /*
- * force cow if csum exists in the range.
- * this ensure that csum for a given extent are
- * either valid or do not exist.
- */
- ret = csum_exist_in_range(fs_info, disk_bytenr,
- num_bytes);
- if (ret) {
- /*
- * ret could be -EIO if the above fails to read
- * metadata.
- */
- if (ret < 0) {
- if (cow_start != (u64)-1)
- cur_offset = cow_start;
- goto error;
- }
- WARN_ON_ONCE(freespace_inode);
- goto out_check;
- }
- /* If the extent's block group is RO, we must COW */
- if (!btrfs_inc_nocow_writers(fs_info, disk_bytenr))
- goto out_check;
+ ret = 0;
+ if (btrfs_inc_nocow_writers(fs_info, nocow_args.disk_bytenr))
nocow = true;
- } else if (extent_type == BTRFS_FILE_EXTENT_INLINE) {
- extent_end = found_key.offset + ram_bytes;
- extent_end = ALIGN(extent_end, fs_info->sectorsize);
- /* Skip extents outside of our requested range */
- if (extent_end <= start) {
- path->slots[0]++;
- goto next_slot;
- }
- } else {
- /* If this triggers then we have a memory corruption */
- BUG();
- }
out_check:
/*
* If nocow is false then record the beginning of the range
@@ -1892,15 +1947,17 @@ static noinline int run_delalloc_nocow(struct btrfs_inode *inode,
cow_start = (u64)-1;
}
+ nocow_end = cur_offset + nocow_args.num_bytes - 1;
+
if (extent_type == BTRFS_FILE_EXTENT_PREALLOC) {
- u64 orig_start = found_key.offset - extent_offset;
+ u64 orig_start = found_key.offset - nocow_args.extent_offset;
struct extent_map *em;
- em = create_io_em(inode, cur_offset, num_bytes,
+ em = create_io_em(inode, cur_offset, nocow_args.num_bytes,
orig_start,
- disk_bytenr, /* block_start */
- num_bytes, /* block_len */
- disk_num_bytes, /* orig_block_len */
+ nocow_args.disk_bytenr, /* block_start */
+ nocow_args.num_bytes, /* block_len */
+ nocow_args.disk_num_bytes, /* orig_block_len */
ram_bytes, BTRFS_COMPRESS_NONE,
BTRFS_ORDERED_PREALLOC);
if (IS_ERR(em)) {
@@ -1909,20 +1966,23 @@ static noinline int run_delalloc_nocow(struct btrfs_inode *inode,
}
free_extent_map(em);
ret = btrfs_add_ordered_extent(inode,
- cur_offset, num_bytes, num_bytes,
- disk_bytenr, num_bytes, 0,
+ cur_offset, nocow_args.num_bytes,
+ nocow_args.num_bytes,
+ nocow_args.disk_bytenr,
+ nocow_args.num_bytes, 0,
1 << BTRFS_ORDERED_PREALLOC,
BTRFS_COMPRESS_NONE);
if (ret) {
btrfs_drop_extent_cache(inode, cur_offset,
- cur_offset + num_bytes - 1,
- 0);
+ nocow_end, 0);
goto error;
}
} else {
ret = btrfs_add_ordered_extent(inode, cur_offset,
- num_bytes, num_bytes,
- disk_bytenr, num_bytes,
+ nocow_args.num_bytes,
+ nocow_args.num_bytes,
+ nocow_args.disk_bytenr,
+ nocow_args.num_bytes,
0,
1 << BTRFS_ORDERED_NOCOW,
BTRFS_COMPRESS_NONE);
@@ -1931,7 +1991,7 @@ static noinline int run_delalloc_nocow(struct btrfs_inode *inode,
}
if (nocow)
- btrfs_dec_nocow_writers(fs_info, disk_bytenr);
+ btrfs_dec_nocow_writers(fs_info, nocow_args.disk_bytenr);
nocow = false;
if (btrfs_is_data_reloc_root(root))
@@ -1941,10 +2001,9 @@ static noinline int run_delalloc_nocow(struct btrfs_inode *inode,
* from freeing metadata of created ordered extent.
*/
ret = btrfs_reloc_clone_csums(inode, cur_offset,
- num_bytes);
+ nocow_args.num_bytes);
- extent_clear_unlock_delalloc(inode, cur_offset,
- cur_offset + num_bytes - 1,
+ extent_clear_unlock_delalloc(inode, cur_offset, nocow_end,
locked_page, EXTENT_LOCKED |
EXTENT_DELALLOC |
EXTENT_CLEAR_DATA_RESV,
@@ -1977,7 +2036,7 @@ static noinline int run_delalloc_nocow(struct btrfs_inode *inode,
error:
if (nocow)
- btrfs_dec_nocow_writers(fs_info, disk_bytenr);
+ btrfs_dec_nocow_writers(fs_info, nocow_args.disk_bytenr);
if (ret && cur_offset < end)
extent_clear_unlock_delalloc(inode, cur_offset, end,
@@ -7114,6 +7173,7 @@ noinline int can_nocow_extent(struct inode *inode, u64 offset, u64 *len,
u64 *ram_bytes, bool strict)
{
struct btrfs_fs_info *fs_info = btrfs_sb(inode->i_sb);
+ struct can_nocow_file_extent_args nocow_args = { 0 };
struct btrfs_path *path;
int ret;
struct extent_buffer *leaf;
@@ -7121,13 +7181,7 @@ noinline int can_nocow_extent(struct inode *inode, u64 offset, u64 *len,
struct extent_io_tree *io_tree = &BTRFS_I(inode)->io_tree;
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;
- bool nocow = (BTRFS_I(inode)->flags & BTRFS_INODE_NODATACOW);
path = btrfs_alloc_path();
if (!path)
@@ -7138,18 +7192,17 @@ noinline int can_nocow_extent(struct inode *inode, u64 offset, u64 *len,
if (ret < 0)
goto out;
- slot = path->slots[0];
if (ret == 1) {
- if (slot == 0) {
+ if (path->slots[0] == 0) {
/* can't find the item, must cow */
ret = 0;
goto out;
}
- slot--;
+ path->slots[0]--;
}
ret = 0;
leaf = path->nodes[0];
- btrfs_item_key_to_cpu(leaf, &key, slot);
+ btrfs_item_key_to_cpu(leaf, &key, path->slots[0]);
if (key.objectid != btrfs_ino(BTRFS_I(inode)) ||
key.type != BTRFS_EXTENT_DATA_KEY) {
/* not our file or wrong item type, must cow */
@@ -7161,57 +7214,38 @@ noinline int can_nocow_extent(struct inode *inode, u64 offset, u64 *len,
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;
- }
-
- if (!nocow && found_type == BTRFS_FILE_EXTENT_REG)
+ if (btrfs_file_extent_end(path) <= offset)
goto out;
- extent_end = key.offset + btrfs_file_extent_num_bytes(leaf, fi);
- if (extent_end <= offset)
- goto out;
+ fi = btrfs_item_ptr(leaf, path->slots[0], struct btrfs_file_extent_item);
+ found_type = btrfs_file_extent_type(leaf, fi);
+ if (ram_bytes)
+ *ram_bytes = btrfs_file_extent_ram_bytes(leaf, fi);
- disk_bytenr = btrfs_file_extent_disk_bytenr(leaf, fi);
- if (disk_bytenr == 0)
- goto out;
+ nocow_args.start = offset;
+ nocow_args.end = offset + *len - 1;
+ nocow_args.strict = strict;
+ nocow_args.free_path = true;
- if (btrfs_file_extent_compression(leaf, fi) ||
- btrfs_file_extent_encryption(leaf, fi) ||
- btrfs_file_extent_other_encoding(leaf, fi))
- goto out;
+ ret = can_nocow_file_extent(path, &key, BTRFS_I(inode), &nocow_args);
+ /* can_nocow_file_extent() has freed the path. */
+ path = NULL;
- /*
- * Do the same check as in btrfs_cross_ref_exist but without the
- * unnecessary search.
- */
- if (!strict &&
- (btrfs_file_extent_generation(leaf, fi) <=
- btrfs_root_last_snapshot(&root->root_item)))
+ if (ret != 1) {
+ /* Treat errors as not being able to NOCOW. */
+ ret = 0;
goto out;
-
- backref_offset = btrfs_file_extent_offset(leaf, fi);
-
- if (orig_start) {
- *orig_start = key.offset - backref_offset;
- *orig_block_len = btrfs_file_extent_disk_num_bytes(leaf, fi);
- *ram_bytes = btrfs_file_extent_ram_bytes(leaf, fi);
}
- btrfs_release_path(path);
-
- if (btrfs_extent_readonly(fs_info, disk_bytenr))
+ ret = 0;
+ if (btrfs_extent_readonly(fs_info, nocow_args.disk_bytenr))
goto out;
- num_bytes = min(offset + *len, extent_end) - offset;
- if (!nocow && found_type == BTRFS_FILE_EXTENT_PREALLOC) {
+ if (!(BTRFS_I(inode)->flags & BTRFS_INODE_NODATACOW) &&
+ found_type == BTRFS_FILE_EXTENT_PREALLOC) {
u64 range_end;
- range_end = round_up(offset + num_bytes,
+ range_end = round_up(offset + nocow_args.num_bytes,
root->fs_info->sectorsize) - 1;
ret = test_range_bit(io_tree, offset, range_end,
EXTENT_DELALLOC, 0, NULL);
@@ -7221,42 +7255,12 @@ noinline int can_nocow_extent(struct inode *inode, u64 offset, u64 *len,
}
}
- /*
- * look for other files referencing this extent, if we
- * find any we must cow
- */
+ if (orig_start)
+ *orig_start = key.offset - nocow_args.extent_offset;
+ if (orig_block_len)
+ *orig_block_len = nocow_args.disk_num_bytes;
- ret = btrfs_cross_ref_exist(root, btrfs_ino(BTRFS_I(inode)),
- key.offset - backref_offset, disk_bytenr,
- strict, path);
- if (ret) {
- ret = 0;
- goto out;
- }
-
- /*
- * We don't need the path anymore, plus through the csum_exist_in_range()
- * call below we will end up allocating another path. So free the path
- * to avoid unnecessary extra memory usage.
- */
- btrfs_free_path(path);
- path = NULL;
-
- /*
- * adjust disk_bytenr and num_bytes to cover just the bytes
- * in this extent we are about to write. If there
- * are any csums in that range we have to cow in order
- * to keep the csums correct
- */
- disk_bytenr += backref_offset;
- disk_bytenr += offset - key.offset;
- if (csum_exist_in_range(fs_info, disk_bytenr, num_bytes))
- goto out;
- /*
- * all of the above have passed, it is safe to overwrite this extent
- * without cow
- */
- *len = num_bytes;
+ *len = nocow_args.num_bytes;
ret = 1;
out:
btrfs_free_path(path);
--
2.33.0
^ permalink raw reply related [flat|nested] 4+ messages in thread