linux-kernel - [RFC v2 4/7] maple_tree: avoid bulk alloc/free to use percpu array more

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Message-ID: <20230810163627.6206-13-vbabka@suse.cz>
Date:   Thu, 10 Aug 2023 18:36:32 +0200
From:   Vlastimil Babka <vbabka@...e.cz>
To:     "Liam R. Howlett" <Liam.Howlett@...cle.com>,
        Matthew Wilcox <willy@...radead.org>,
        Suren Baghdasaryan <surenb@...gle.com>,
        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 v2 4/7] 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 for now is just to convert the respective maple tree
wrappers to do a loop of normal alloc/free. We can optimize later
versions if needed.
---
 lib/maple_tree.c | 12 ++++++++++--
 1 file changed, 10 insertions(+), 2 deletions(-)

diff --git a/lib/maple_tree.c b/lib/maple_tree.c
index 1196d0a17f03..926bee7a274a 100644
--- a/lib/maple_tree.c
+++ b/lib/maple_tree.c
@@ -161,12 +161,20 @@ 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 i;
+
+	for (i = 0; i < size; i++) {
+		nodes[i] = kmem_cache_alloc(maple_node_cache, gfp);
+		if (!nodes[i])
+			break;
+	}
+	return i;
 }
 
 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