From: Filipe Manana <fdmanana@xxxxxxxx>
commit d47704bd1c78c85831561bcf701b90dd66f811b2 upstream.
At find_delalloc_subrange(), when we need to get the next extent map, we
do a full search on the extent map tree (a red black tree). This is fine
but it's a lot more efficient to simply use rb_next(), which typically
requires iterating over less nodes of the tree and never needs to compare
the ranges of nodes with the one we are looking for.
So add a public helper to extent_map.{h,c} to get the extent map that
immediately follows another extent map, using rb_next(), and use that
helper at find_delalloc_subrange().
Signed-off-by: Filipe Manana <fdmanana@xxxxxxxx>
Signed-off-by: David Sterba <dsterba@xxxxxxxx>
---
Please add this patch to the next 6.1 stable release.
It happens to fix a bug recently reported at:
https://bugzilla.redhat.com/show_bug.cgi?id=2187312
Thanks.
fs/btrfs/extent_map.c | 31 +++++++++++++++++++++++++++++-
fs/btrfs/extent_map.h | 2 ++
fs/btrfs/file.c | 44 ++++++++++++++++++++++++++-----------------
3 files changed, 59 insertions(+), 18 deletions(-)
diff --git a/fs/btrfs/extent_map.c b/fs/btrfs/extent_map.c
index b8ae02aa632e..4abbe4b35253 100644
--- a/fs/btrfs/extent_map.c
+++ b/fs/btrfs/extent_map.c
@@ -523,7 +523,7 @@ void replace_extent_mapping(struct extent_map_tree *tree,
setup_extent_mapping(tree, new, modified);
}
-static struct extent_map *next_extent_map(struct extent_map *em)
+static struct extent_map *next_extent_map(const struct extent_map *em)
{
struct rb_node *next;
@@ -533,6 +533,35 @@ static struct extent_map *next_extent_map(struct extent_map *em)
return container_of(next, struct extent_map, rb_node);
}
+/*
+ * Get the extent map that immediately follows another one.
+ *
+ * @tree: The extent map tree that the extent map belong to.
+ * Holding read or write access on the tree's lock is required.
+ * @em: An extent map from the given tree. The caller must ensure that
+ * between getting @em and between calling this function, the
+ * extent map @em is not removed from the tree - for example, by
+ * holding the tree's lock for the duration of those 2 operations.
+ *
+ * Returns the extent map that immediately follows @em, or NULL if @em is the
+ * last extent map in the tree.
+ */
+struct extent_map *btrfs_next_extent_map(const struct extent_map_tree *tree,
+ const struct extent_map *em)
+{
+ struct extent_map *next;
+
+ /* The lock must be acquired either in read mode or write mode. */
+ lockdep_assert_held(&tree->lock);
+ ASSERT(extent_map_in_tree(em));
+
+ next = next_extent_map(em);
+ if (next)
+ refcount_inc(&next->refs);
+
+ return next;
+}
+
static struct extent_map *prev_extent_map(struct extent_map *em)
{
struct rb_node *prev;
diff --git a/fs/btrfs/extent_map.h b/fs/btrfs/extent_map.h
index ad311864272a..68d3f2c9ea1d 100644
--- a/fs/btrfs/extent_map.h
+++ b/fs/btrfs/extent_map.h
@@ -87,6 +87,8 @@ static inline u64 extent_map_block_end(struct extent_map *em)
void extent_map_tree_init(struct extent_map_tree *tree);
struct extent_map *lookup_extent_mapping(struct extent_map_tree *tree,
u64 start, u64 len);
+struct extent_map *btrfs_next_extent_map(const struct extent_map_tree *tree,
+ const struct extent_map *em);
int add_extent_mapping(struct extent_map_tree *tree,
struct extent_map *em, int modified);
void remove_extent_mapping(struct extent_map_tree *tree, struct extent_map *em);
diff --git a/fs/btrfs/file.c b/fs/btrfs/file.c
index 1bda59c68360..77202addead8 100644
--- a/fs/btrfs/file.c
+++ b/fs/btrfs/file.c
@@ -3248,40 +3248,50 @@ static bool find_delalloc_subrange(struct btrfs_inode *inode, u64 start, u64 end
*/
read_lock(&em_tree->lock);
em = lookup_extent_mapping(em_tree, start, len);
- read_unlock(&em_tree->lock);
+ if (!em) {
+ read_unlock(&em_tree->lock);
+ return (delalloc_len > 0);
+ }
/* extent_map_end() returns a non-inclusive end offset. */
- em_end = em ? extent_map_end(em) : 0;
+ em_end = extent_map_end(em);
/*
* If we have a hole/prealloc extent map, check the next one if this one
* ends before our range's end.
*/
- if (em && (em->block_start == EXTENT_MAP_HOLE ||
- test_bit(EXTENT_FLAG_PREALLOC, &em->flags)) && em_end < end) {
+ if ((em->block_start == EXTENT_MAP_HOLE ||
+ test_bit(EXTENT_FLAG_PREALLOC, &em->flags)) && em_end < end) {
struct extent_map *next_em;
- read_lock(&em_tree->lock);
- next_em = lookup_extent_mapping(em_tree, em_end, len - em_end);
- read_unlock(&em_tree->lock);
-
+ next_em = btrfs_next_extent_map(em_tree, em);
free_extent_map(em);
- em_end = next_em ? extent_map_end(next_em) : 0;
+
+ /*
+ * There's no next extent map or the next one starts beyond our
+ * range, return the range found in the io tree (if any).
+ */
+ if (!next_em || next_em->start > end) {
+ read_unlock(&em_tree->lock);
+ free_extent_map(next_em);
+ return (delalloc_len > 0);
+ }
+
+ em_end = extent_map_end(next_em);
em = next_em;
}
- if (em && (em->block_start == EXTENT_MAP_HOLE ||
- test_bit(EXTENT_FLAG_PREALLOC, &em->flags))) {
- free_extent_map(em);
- em = NULL;
- }
+ read_unlock(&em_tree->lock);
/*
- * No extent map or one for a hole or prealloc extent. Use the delalloc
- * range we found in the io tree if we have one.
+ * We have a hole or prealloc extent that ends at or beyond our range's
+ * end, return the range found in the io tree (if any).
*/
- if (!em)
+ if (em->block_start == EXTENT_MAP_HOLE ||
+ test_bit(EXTENT_FLAG_PREALLOC, &em->flags)) {
+ free_extent_map(em);
return (delalloc_len > 0);
+ }
/*
* We don't have any range as EXTENT_DELALLOC in the io tree, so the
--
2.34.1
