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

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Message-ID: <20230810163627.6206-15-vbabka@suse.cz>
Date:   Thu, 10 Aug 2023 18:36:34 +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 6/7] maple_tree: replace preallocation with slub percpu array prefill

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