[RFC v2 6/7] maple_tree: replace preallocation with slub percpu array prefill

[Vlastimil Babka]

With the percpu array we can try not doing the preallocations in maple
tree, and instead make sure the percpu array is prefilled, and using
GFP_ATOMIC in places that relied on the preallocation (in case we miss
or fail trylock on the array), i.e. mas_store_prealloc(). For now simply
add __GFP_NOFAIL there as well.
---
 lib/maple_tree.c | 20 +++++++++-----------
 1 file changed, 9 insertions(+), 11 deletions(-)

diff --git a/lib/maple_tree.c b/lib/maple_tree.c
index 8bd4a79537d8..304f2453fac9 100644
--- a/lib/maple_tree.c
+++ b/lib/maple_tree.c
@@ -5530,7 +5530,12 @@ void mas_store_prealloc(struct ma_state *mas, void *entry)
 
 	mas_wr_store_setup(&wr_mas);
 	trace_ma_write(__func__, mas, 0, entry);
+
+retry:
 	mas_wr_store_entry(&wr_mas);
+	if (unlikely(mas_nomem(mas, GFP_ATOMIC | __GFP_NOFAIL)))
+		goto retry;
+
 	MAS_WR_BUG_ON(&wr_mas, mas_is_err(mas));
 	mas_destroy(mas);
 }
@@ -5545,19 +5550,12 @@ EXPORT_SYMBOL_GPL(mas_store_prealloc);
  */
 int mas_preallocate(struct ma_state *mas, gfp_t gfp)
 {
-	int ret;
+	int count = 1 + mas_mt_height(mas) * 3;
 
-	mas_node_count_gfp(mas, 1 + mas_mt_height(mas) * 3, gfp);
-	mas->mas_flags |= MA_STATE_PREALLOC;
-	if (likely(!mas_is_err(mas)))
-		return 0;
+	// TODO: should probably indicate if it failed the prefill?
+	kmem_cache_prefill_percpu_array(maple_node_cache, count, gfp);
 
-	mas_set_alloc_req(mas, 0);
-	ret = xa_err(mas->node);
-	mas_reset(mas);
-	mas_destroy(mas);
-	mas_reset(mas);
-	return ret;
+	return 0;
 }
 EXPORT_SYMBOL_GPL(mas_preallocate);
 
-- 
2.41.0