Re: [RFC v1 5/5] maple_tree: replace preallocation with slub percpu array prefill

["Liam R. Howlett" <Liam.Howlett@Oracle.com>]

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* Vlastimil Babka <vbabka@suse.cz> [230808 05:53]:
> 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.
> 
> First I tried to change mas_node_count_gfp() to not preallocate anything
> anywhere, but that lead to warns and panics, even though the other
> caller mas_node_count() uses GFP_NOWAIT | __GFP_NOWARN so it has no
> guarantees... So I changed just mas_preallocate(). I let it still to
> truly preallocate a single node, but maybe it's not necessary?

Here's a patch to add the percpu array interface to the testing code.

Note that the maple tree preallocation testing isn't updated.

> ---
>  lib/maple_tree.c | 10 ++++++++--
>  1 file changed, 8 insertions(+), 2 deletions(-)
> 
> diff --git a/lib/maple_tree.c b/lib/maple_tree.c
> index 7a8e7c467d7c..5a209d88c318 100644
> --- a/lib/maple_tree.c
> +++ b/lib/maple_tree.c
> @@ -5534,7 +5534,12 @@ 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);
>  }
> @@ -5550,9 +5555,10 @@ 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;
> +	mas_node_count_gfp(mas, 1, gfp);
> +	kmem_cache_prefill_percpu_array(maple_node_cache, count, gfp);
>  	if (likely(!mas_is_err(mas)))
>  		return 0;
>  
> -- 
> 2.41.0
> 

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From 3d4ac32997cab4fc8e957deb4a58a5a7afa485bc Mon Sep 17 00:00:00 2001
From: "Liam R. Howlett" <Liam.Howlett@oracle.com>
Date: Tue, 8 Aug 2023 14:58:13 -0400
Subject: [PATCH] tools: Add SLUB percpu array functions for testing

Support new percpu array functions to the test code so they can be used
in the maple tree testing.

Signed-off-by: Liam R. Howlett <Liam.Howlett@oracle.com>
---
 tools/include/linux/slab.h              |  4 ++++
 tools/testing/radix-tree/linux.c        | 14 ++++++++++++++
 tools/testing/radix-tree/linux/kernel.h |  1 +
 3 files changed, 19 insertions(+)

diff --git a/tools/include/linux/slab.h b/tools/include/linux/slab.h
index 311759ea25e9..1043f9c5ef4e 100644
--- a/tools/include/linux/slab.h
+++ b/tools/include/linux/slab.h
@@ -7,6 +7,7 @@
 
 #define SLAB_PANIC 2
 #define SLAB_RECLAIM_ACCOUNT    0x00020000UL            /* Objects are reclaimable */
+#define SLAB_NO_MERGE		0x01000000UL		/* Prevent merging with compatible kmem caches */
 
 #define kzalloc_node(size, flags, node) kmalloc(size, flags)
 
@@ -45,4 +46,7 @@ void kmem_cache_free_bulk(struct kmem_cache *cachep, size_t size, void **list);
 int kmem_cache_alloc_bulk(struct kmem_cache *cachep, gfp_t gfp, size_t size,
 			  void **list);
 
+int kmem_cache_setup_percpu_array(struct kmem_cache *s, unsigned int count);
+int kmem_cache_prefill_percpu_array(struct kmem_cache *s, unsigned int count,
+		gfp_t gfp);
 #endif		/* _TOOLS_SLAB_H */
diff --git a/tools/testing/radix-tree/linux.c b/tools/testing/radix-tree/linux.c
index d587a558997f..cbe7937fdd5e 100644
--- a/tools/testing/radix-tree/linux.c
+++ b/tools/testing/radix-tree/linux.c
@@ -187,6 +187,20 @@ int kmem_cache_alloc_bulk(struct kmem_cache *cachep, gfp_t gfp, size_t size,
 	return size;
 }
 
+int kmem_cache_setup_percpu_array(struct kmem_cache *s, unsigned int count)
+{
+	return 0;
+}
+
+int kmem_cache_prefill_percpu_array(struct kmem_cache *s, unsigned int count,
+		gfp_t gfp)
+{
+	if (count > s->non_kernel)
+		return s->non_kernel;
+
+	return count;
+}
+
 struct kmem_cache *
 kmem_cache_create(const char *name, unsigned int size, unsigned int align,
 		unsigned int flags, void (*ctor)(void *))
diff --git a/tools/testing/radix-tree/linux/kernel.h b/tools/testing/radix-tree/linux/kernel.h
index c5c9d05f29da..fc75018974de 100644
--- a/tools/testing/radix-tree/linux/kernel.h
+++ b/tools/testing/radix-tree/linux/kernel.h
@@ -15,6 +15,7 @@
 
 #define printk printf
 #define pr_err printk
+#define pr_warn printk
 #define pr_info printk
 #define pr_debug printk
 #define pr_cont printk
-- 
2.39.2