int order, i;
struct ext4_inode_info *ei = EXT4_I(ac->ac_inode);
struct ext4_locality_group *lg;
- struct ext4_prealloc_space *tmp_pa, *cpa = NULL;
- ext4_lblk_t tmp_pa_start, tmp_pa_end;
+ struct ext4_prealloc_space *tmp_pa = NULL, *cpa = NULL;
+ loff_t tmp_pa_end;
struct rb_node *iter;
ext4_fsblk_t goal_block;
if (!(ac->ac_flags & EXT4_MB_HINT_DATA))
return false;
- /* first, try per-file preallocation */
+ /*
+ * first, try per-file preallocation by searching the inode pa rbtree.
+ *
+ * Here, we can't do a direct traversal of the tree because
+ * ext4_mb_discard_group_preallocation() can paralelly mark the pa
+ * deleted and that can cause direct traversal to skip some entries.
+ */
read_lock(&ei->i_prealloc_lock);
+
+ if (RB_EMPTY_ROOT(&ei->i_prealloc_node)) {
+ goto try_group_pa;
+ }
+
+ /*
+ * Step 1: Find a pa with logical start immediately adjacent to the
+ * original logical start. This could be on the left or right.
+ *
+ * (tmp_pa->pa_lstart never changes so we can skip locking for it).
+ */
for (iter = ei->i_prealloc_node.rb_node; iter;
iter = ext4_mb_pa_rb_next_iter(ac->ac_o_ex.fe_logical,
- tmp_pa_start, iter)) {
+ tmp_pa->pa_lstart, iter)) {
tmp_pa = rb_entry(iter, struct ext4_prealloc_space,
pa_node.inode_node);
+ }
- /* all fields in this condition don't change,
- * so we can skip locking for them */
- tmp_pa_start = tmp_pa->pa_lstart;
- tmp_pa_end = tmp_pa->pa_lstart + EXT4_C2B(sbi, tmp_pa->pa_len);
-
- /* original request start doesn't lie in this PA */
- if (ac->ac_o_ex.fe_logical < tmp_pa_start ||
- ac->ac_o_ex.fe_logical >= tmp_pa_end)
- continue;
+ /*
+ * Step 2: The adjacent pa might be to the right of logical start, find
+ * the left adjacent pa. After this step we'd have a valid tmp_pa whose
+ * logical start is towards the left of original request's logical start
+ */
+ if (tmp_pa->pa_lstart > ac->ac_o_ex.fe_logical) {
+ struct rb_node *tmp;
+ tmp = rb_prev(&tmp_pa->pa_node.inode_node);
- /* non-extent files can't have physical blocks past 2^32 */
- if (!(ext4_test_inode_flag(ac->ac_inode, EXT4_INODE_EXTENTS)) &&
- (tmp_pa->pa_pstart + EXT4_C2B(sbi, tmp_pa->pa_len) >
- EXT4_MAX_BLOCK_FILE_PHYS)) {
+ if (tmp) {
+ tmp_pa = rb_entry(tmp, struct ext4_prealloc_space,
+ pa_node.inode_node);
+ } else {
/*
- * Since PAs don't overlap, we won't find any
- * other PA to satisfy this.
+ * If there is no adjacent pa to the left then finding
+ * an overlapping pa is not possible hence stop searching
+ * inode pa tree
*/
- break;
+ goto try_group_pa;
}
+ }
- /* found preallocated blocks, use them */
+ BUG_ON(!(tmp_pa && tmp_pa->pa_lstart <= ac->ac_o_ex.fe_logical));
+
+ /*
+ * Step 3: If the left adjacent pa is deleted, keep moving left to find
+ * the first non deleted adjacent pa. After this step we should have a
+ * valid tmp_pa which is guaranteed to be non deleted.
+ */
+ for (iter = &tmp_pa->pa_node.inode_node;; iter = rb_prev(iter)) {
+ if (!iter) {
+ /*
+ * no non deleted left adjacent pa, so stop searching
+ * inode pa tree
+ */
+ goto try_group_pa;
+ }
+ tmp_pa = rb_entry(iter, struct ext4_prealloc_space,
+ pa_node.inode_node);
spin_lock(&tmp_pa->pa_lock);
- if (tmp_pa->pa_deleted == 0 && tmp_pa->pa_free &&
- likely(ext4_mb_pa_goal_check(ac, tmp_pa))) {
- atomic_inc(&tmp_pa->pa_count);
- ext4_mb_use_inode_pa(ac, tmp_pa);
+ if (tmp_pa->pa_deleted == 0) {
+ /*
+ * We will keep holding the pa_lock from
+ * this point on because we don't want group discard
+ * to delete this pa underneath us. Since group
+ * discard is anyways an ENOSPC operation it
+ * should be okay for it to wait a few more cycles.
+ */
+ break;
+ } else {
spin_unlock(&tmp_pa->pa_lock);
- read_unlock(&ei->i_prealloc_lock);
- return true;
}
+ }
+
+ BUG_ON(!(tmp_pa && tmp_pa->pa_lstart <= ac->ac_o_ex.fe_logical));
+ BUG_ON(tmp_pa->pa_deleted == 1);
+
+ /*
+ * Step 4: We now have the non deleted left adjacent pa. Only this
+ * pa can possibly satisfy the request hence check if it overlaps
+ * original logical start and stop searching if it doesn't.
+ */
+ tmp_pa_end = (loff_t)tmp_pa->pa_lstart + EXT4_C2B(sbi, tmp_pa->pa_len);
+
+ if (ac->ac_o_ex.fe_logical >= tmp_pa_end) {
+ spin_unlock(&tmp_pa->pa_lock);
+ goto try_group_pa;
+ }
+
+ /* non-extent files can't have physical blocks past 2^32 */
+ if (!(ext4_test_inode_flag(ac->ac_inode, EXT4_INODE_EXTENTS)) &&
+ (tmp_pa->pa_pstart + EXT4_C2B(sbi, tmp_pa->pa_len) >
+ EXT4_MAX_BLOCK_FILE_PHYS)) {
+ /*
+ * Since PAs don't overlap, we won't find any other PA to
+ * satisfy this.
+ */
spin_unlock(&tmp_pa->pa_lock);
+ goto try_group_pa;
+ }
+
+ if (tmp_pa->pa_free && likely(ext4_mb_pa_goal_check(ac, tmp_pa))) {
+ atomic_inc(&tmp_pa->pa_count);
+ ext4_mb_use_inode_pa(ac, tmp_pa);
+ spin_unlock(&tmp_pa->pa_lock);
+ read_unlock(&ei->i_prealloc_lock);
+ return true;
+ } else {
+ /*
+ * We found a valid overlapping pa but couldn't use it because
+ * it had no free blocks. This should ideally never happen
+ * because:
+ *
+ * 1. When a new inode pa is added to rbtree it must have
+ * pa_free > 0 since otherwise we won't actually need
+ * preallocation.
+ *
+ * 2. An inode pa that is in the rbtree can only have it's
+ * pa_free become zero when another thread calls:
+ * ext4_mb_new_blocks
+ * ext4_mb_use_preallocated
+ * ext4_mb_use_inode_pa
+ *
+ * 3. Further, after the above calls make pa_free == 0, we will
+ * immediately remove it from the rbtree in:
+ * ext4_mb_new_blocks
+ * ext4_mb_release_context
+ * ext4_mb_put_pa
+ *
+ * 4. Since the pa_free becoming 0 and pa_free getting removed
+ * from tree both happen in ext4_mb_new_blocks, which is always
+ * called with i_data_sem held for data allocations, we can be
+ * sure that another process will never see a pa in rbtree with
+ * pa_free == 0.
+ */
+ WARN_ON_ONCE(tmp_pa->pa_free == 0);
}
+ spin_unlock(&tmp_pa->pa_lock);
+try_group_pa:
read_unlock(&ei->i_prealloc_lock);
/* can we use group allocation? */
projects / users / hch / configfs.git / commitdiff