linux-kernel - [RFC v1 4/5] maple_tree: avoid bulk alloc/free to use percpu array more

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Date:   Tue,  8 Aug 2023 11:53:47 +0200
From:   Vlastimil Babka <vbabka@...e.cz>
To:     "Liam R. Howlett" <Liam.Howlett@...cle.com>,
        Matthew Wilcox <willy@...radead.org>,
        Christoph Lameter <cl@...ux.com>,
        David Rientjes <rientjes@...gle.com>,
        Pekka Enberg <penberg@...nel.org>,
        Joonsoo Kim <iamjoonsoo.kim@....com>
Cc:     Hyeonggon Yoo <42.hyeyoo@...il.com>,
        Roman Gushchin <roman.gushchin@...ux.dev>, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org, patches@...ts.linux.dev,
        Vlastimil Babka <vbabka@...e.cz>
Subject: [RFC v1 4/5] maple_tree: avoid bulk alloc/free to use percpu array more

Using bulk alloc/free on a cache with percpu array should not be
necessary and the bulk alloc actually bypasses the array (the prefill
functionality currently relies on this).

The simplest change is just to convert the respective maple tree
wrappers to do a loop of normal alloc/free.
---
 lib/maple_tree.c | 11 +++++++++--
 1 file changed, 9 insertions(+), 2 deletions(-)

diff --git a/lib/maple_tree.c b/lib/maple_tree.c
index 1196d0a17f03..7a8e7c467d7c 100644
--- a/lib/maple_tree.c
+++ b/lib/maple_tree.c
@@ -161,12 +161,19 @@ static inline struct maple_node *mt_alloc_one(gfp_t gfp)
 
 static inline int mt_alloc_bulk(gfp_t gfp, size_t size, void **nodes)
 {
-	return kmem_cache_alloc_bulk(maple_node_cache, gfp, size, nodes);
+	int allocated = 0;
+	for (size_t i = 0; i < size; i++) {
+		nodes[i] = kmem_cache_alloc(maple_node_cache, gfp);
+		if (nodes[i])
+			allocated++;
+	}
+	return allocated;
 }
 
 static inline void mt_free_bulk(size_t size, void __rcu **nodes)
 {
-	kmem_cache_free_bulk(maple_node_cache, size, (void **)nodes);
+	for (size_t i = 0; i < size; i++)
+		kmem_cache_free(maple_node_cache, nodes[i]);
 }
 
 static void mt_free_rcu(struct rcu_head *head)
-- 
2.41.0