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

Liam R. Howlett
2023-08-08T19:04:06Z

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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