Btrfs: Only prep for btree deletion balances when nodes are mostly empty (7b78c170) · Commits · 戴 / test

Whenever an item deletion is done, we need to balance all the nodes in the tree to make sure we don't end up with an empty node if a pointer is deleted. This balance prep happens from the root of the tree down so we can drop our locks as we go. reada_for_balance was triggering read-ahead on neighboring nodes even when no balancing was required. This adds an extra check to avoid calling balance_level() and avoid reada_for_balance() when a balance won't be required. Signed-off-by:

Chris Mason <chris.mason@oracle.com>

fs/btrfs/ctree.c

+6 −3

Original line number	Diff line number	Diff line
		@@ -1518,18 +1518,19 @@ again:
		*/
		if (prealloc_block.objectid &&
		prealloc_block.offset != b->len) {
		btrfs_set_path_blocking(p);
		btrfs_release_path(root, p);
		btrfs_free_reserved_extent(root,
		prealloc_block.objectid,
		prealloc_block.offset);
		prealloc_block.objectid = 0;
		goto again;
		}

		/*
		* for higher level blocks, try not to allocate blocks
		* with the block and the parent locks held.
		*/
		if (level > 1 && !prealloc_block.objectid &&
		if (level > 0 && !prealloc_block.objectid &&
		btrfs_path_lock_waiting(p, level)) {
		u32 size = b->len;
		u64 hint = b->start;
		@@ -1614,7 +1615,9 @@ cow_done:
		}
		b = p->nodes[level];
		slot = p->slots[level];
		} else if (ins_len < 0) {
		} else if (ins_len < 0 &&
		btrfs_header_nritems(b) <
		BTRFS_NODEPTRS_PER_BLOCK(root) / 4) {
		int sret;

		sret = reada_for_balance(root, p, level);

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