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xfs: add comments documenting the rebalance algorithm
Reported-by: Brian Foster <bfoster@redhat.com> Signed-off-by: Christoph Hellwig <hch@lst.de> Reviewed-by: Brian Foster <bfoster@redhat.com> Reviewed-by: Darrick J. Wong <darrick.wong@oracle.com> Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
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@ -672,6 +672,11 @@ xfs_iext_rebalance_node(
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struct xfs_iext_node *node,
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int nr_entries)
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{
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/*
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* If the neighbouring nodes are completely full, or have different
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* parents, we might never be able to merge our node, and will only
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* delete it once the number of entries hits zero.
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*/
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if (nr_entries == 0)
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return node;
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@ -693,6 +698,11 @@ xfs_iext_rebalance_node(
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int nr_next = xfs_iext_node_nr_entries(next, 0), i;
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if (nr_entries + nr_next <= KEYS_PER_NODE) {
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/*
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* Merge the next node into this node so that we don't
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* have to do an additional update of the keys in the
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* higher levels.
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*/
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for (i = 0; i < nr_next; i++) {
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node->keys[nr_entries + i] = next->keys[i];
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node->ptrs[nr_entries + i] = next->ptrs[i];
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@ -741,6 +751,11 @@ xfs_iext_remove_node(
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return;
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if (level < ifp->if_height) {
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/*
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* If we aren't at the root yet try to find a neighbour node to
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* merge with (or delete the node if it is empty), and then
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* recurse up to the next level.
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*/
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level++;
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parent = xfs_iext_find_level(ifp, offset, level);
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pos = xfs_iext_node_pos(parent, offset);
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@ -755,6 +770,10 @@ xfs_iext_remove_node(
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goto again;
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}
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} else if (nr_entries == 1) {
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/*
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* If we are at the root and only one entry is left we can just
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* free this node and update the root pointer.
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*/
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ASSERT(node == ifp->if_u1.if_root);
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ifp->if_u1.if_root = node->ptrs[0];
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ifp->if_height--;
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@ -789,6 +808,11 @@ xfs_iext_rebalance_leaf(
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int nr_next = xfs_iext_leaf_nr_entries(ifp, leaf->next, 0), i;
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if (fill + nr_next <= RECS_PER_LEAF) {
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/*
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* Merge the next node into this node so that we don't
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* have to do an additional update of the keys in the
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* higher levels.
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*/
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for (i = 0; i < nr_next; i++)
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leaf->recs[fill + i] = leaf->next->recs[i];
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