On Wed, Sep 10, 2025 at 1:01 AM Vlastimil Babka <vbabka@suse.cz> wrote:
>
> From: "Liam R. Howlett" <Liam.Howlett@Oracle.com>
>
> The fast path through a write will require replacing a single node in
> the tree. Using a sheaf (32 nodes) is too heavy for the fast path, so
> special case the node store operation by just allocating one node in the
> maple state.
>
> Signed-off-by: Liam R. Howlett <Liam.Howlett@Oracle.com>
> Signed-off-by: Vlastimil Babka <vbabka@suse.cz>
> ---
> include/linux/maple_tree.h | 4 +++-
> lib/maple_tree.c | 47 +++++++++++++++++++++++++++++++++++-----
> tools/testing/radix-tree/maple.c | 9 ++++++--
> 3 files changed, 51 insertions(+), 9 deletions(-)
>
> diff --git a/include/linux/maple_tree.h b/include/linux/maple_tree.h
> index 166fd67e00d882b1e6de1f80c1b590bba7497cd3..562a1e9e5132b5b1fa8f8402a7cadd8abb65e323 100644
> --- a/include/linux/maple_tree.h
> +++ b/include/linux/maple_tree.h
> @@ -443,6 +443,7 @@ struct ma_state {
> unsigned long min; /* The minimum index of this node - implied pivot min */
> unsigned long max; /* The maximum index of this node - implied pivot max */
> struct slab_sheaf *sheaf; /* Allocated nodes for this operation */
> + struct maple_node *alloc; /* allocated nodes */
> unsigned long node_request;
> enum maple_status status; /* The status of the state (active, start, none, etc) */
> unsigned char depth; /* depth of tree descent during write */
> @@ -491,8 +492,9 @@ struct ma_wr_state {
> .status = ma_start, \
> .min = 0, \
> .max = ULONG_MAX, \
> - .node_request= 0, \
> .sheaf = NULL, \
> + .alloc = NULL, \
> + .node_request= 0, \
> .mas_flags = 0, \
> .store_type = wr_invalid, \
> }
> diff --git a/lib/maple_tree.c b/lib/maple_tree.c
> index a3fcb20227e506ed209554cc8c041a53f7ef4903..a912e6a1d4378e72b967027b60f8f564476ad14e 100644
> --- a/lib/maple_tree.c
> +++ b/lib/maple_tree.c
> @@ -1073,16 +1073,23 @@ static int mas_ascend(struct ma_state *mas)
> *
> * Return: A pointer to a maple node.
> */
> -static inline struct maple_node *mas_pop_node(struct ma_state *mas)
> +static __always_inline struct maple_node *mas_pop_node(struct ma_state *mas)
> {
> struct maple_node *ret;
>
> + if (mas->alloc) {
> + ret = mas->alloc;
> + mas->alloc = NULL;
> + goto out;
> + }
> +
> if (WARN_ON_ONCE(!mas->sheaf))
> return NULL;
>
> ret = kmem_cache_alloc_from_sheaf(maple_node_cache, GFP_NOWAIT, mas->sheaf);
> - memset(ret, 0, sizeof(*ret));
>
> +out:
> + memset(ret, 0, sizeof(*ret));
> return ret;
> }
>
> @@ -1093,9 +1100,34 @@ static inline struct maple_node *mas_pop_node(struct ma_state *mas)
> */
> static inline void mas_alloc_nodes(struct ma_state *mas, gfp_t gfp)
> {
> - if (unlikely(mas->sheaf)) {
> - unsigned long refill = mas->node_request;
> + if (!mas->node_request)
> + return;
> +
> + if (mas->node_request == 1) {
> + if (mas->sheaf)
> + goto use_sheaf;
Hmm, I don't get the above logic. One node is requested and instead of
using possibly available mas->alloc, we jump to using mas->sheaf and
freeing mas->alloc... That does not sound efficient. What am I
missing?
> +
> + if (mas->alloc)
> + return;
>
> + mas->alloc = mt_alloc_one(gfp);
> + if (!mas->alloc)
> + goto error;
> +
> + mas->node_request = 0;
> + return;
> + }
> +
> +use_sheaf:
> + if (unlikely(mas->alloc)) {
> + kfree(mas->alloc);
> + mas->alloc = NULL;
> + }
> +
> + if (mas->sheaf) {
> + unsigned long refill;
> +
> + refill = mas->node_request;
> if(kmem_cache_sheaf_size(mas->sheaf) >= refill) {
> mas->node_request = 0;
> return;
> @@ -5180,8 +5212,11 @@ void mas_destroy(struct ma_state *mas)
> mas->node_request = 0;
> if (mas->sheaf)
> mt_return_sheaf(mas->sheaf);
> -
> mas->sheaf = NULL;
> +
> + if (mas->alloc)
> + kfree(mas->alloc);
> + mas->alloc = NULL;
> }
> EXPORT_SYMBOL_GPL(mas_destroy);
>
> @@ -5816,7 +5851,7 @@ bool mas_nomem(struct ma_state *mas, gfp_t gfp)
> mas_alloc_nodes(mas, gfp);
> }
>
> - if (!mas->sheaf)
> + if (!mas->sheaf && !mas->alloc)
> return false;
>
> mas->status = ma_start;
> diff --git a/tools/testing/radix-tree/maple.c b/tools/testing/radix-tree/maple.c
> index 72a8fe8e832a4150c6567b711768eba6a3fa6768..83260f2efb1990b71093e456950069c24d75560e 100644
> --- a/tools/testing/radix-tree/maple.c
> +++ b/tools/testing/radix-tree/maple.c
> @@ -35085,10 +35085,15 @@ static unsigned char get_vacant_height(struct ma_wr_state *wr_mas, void *entry)
>
> static int mas_allocated(struct ma_state *mas)
> {
> + int total = 0;
> +
> + if (mas->alloc)
> + total++;
> +
> if (mas->sheaf)
> - return kmem_cache_sheaf_size(mas->sheaf);
> + total += kmem_cache_sheaf_size(mas->sheaf);
>
> - return 0;
> + return total;
> }
> /* Preallocation testing */
> static noinline void __init check_prealloc(struct maple_tree *mt)
>
> --
> 2.51.0
>