maple_tree: Refine mas_preallocate() node calculations

Calculate the number of nodes based on the pending write action instead
of assuming the worst case.

This addresses a performance regression introduced in platforms that
have longer allocation timing.

Signed-off-by: Liam R. Howlett <Liam.Howlett@oracle.com>

diff --git a/lib/maple_tree.c b/lib/maple_tree.c
index 4d312aea2263a080b4121105170cb7bf5adeb4a5..fa40b9d6c35b01c579d70a6b0fc265ff8f3058dd 100644 (file)
--- a/lib/maple_tree.c
+++ b/lib/maple_tree.c
@@ -5809,9 +5809,61 @@ EXPORT_SYMBOL_GPL(mas_store_prealloc);
  */
 int mas_preallocate(struct ma_state *mas, void *entry, gfp_t gfp)
 {
+       MA_WR_STATE(wr_mas, mas, entry);
+       unsigned char node_size;
+       int request = 1;
        int ret;
 
-       mas_node_count_gfp(mas, 1 + mas_mt_height(mas) * 3, gfp);
+
+       if (unlikely(!mas->index && mas->last == ULONG_MAX))
+               goto ask_now;
+
+       mas_wr_store_setup(&wr_mas);
+       wr_mas.content = mas_start(mas);
+       /* Root expand */
+       if (mas_is_none(mas) || mas_is_ptr(mas))
+               goto ask_now;
+
+       if (unlikely(!mas_wr_walk(&wr_mas))) {
+               /* Spanning store, use worst case for now */
+               request = 1 + mas_mt_height(mas) * 3;
+               goto ask_now;
+       }
+
+       /* At this point, we are at the leaf node that needs to be altered. */
+       /* Exact fit, no nodes needed. */
+       if (wr_mas.r_min == mas->index && wr_mas.r_max == mas->last)
+               return 0;
+
+       /* More complicated cases need to expand null and use new node size */
+       mas_wr_end_piv(&wr_mas);
+       if (!entry)
+               mas_wr_extend_null(&wr_mas);
+
+       node_size = mas_wr_node_size(&wr_mas);
+       if (node_size >= mt_slots[wr_mas.type]) {
+               /* Slot store is possible in some cases */
+               if ((node_size == mt_slots[wr_mas.type]) &&
+                   (wr_mas.r_min == mas->index || wr_mas.r_max == mas->last))
+                       goto ask_now;
+               /* Split, worst case for now. */
+               request = 1 + mas_mt_height(mas) * 2;
+               goto ask_now;
+       }
+
+       /* New root needs a singe node */
+       if (mte_is_root(mas->node))
+               goto ask_now;
+
+       /* Potential spanning rebalance, use worst case for now */
+       if (node_size  - 1 <= mt_min_slots[wr_mas.type]) {
+               request = 1 + mas_mt_height(mas) * 3;
+               goto ask_now;
+       }
+
+       /* node store, slot store needs one node */
+ask_now:
+       mas_node_count_gfp(mas, request, gfp);
        mas->mas_flags |= MA_STATE_PREALLOC;
        if (likely(!mas_is_err(mas)))
                return 0;