On Wed, Jul 23, 2025 at 6:35 AM Vlastimil Babka <vba...@suse.cz> wrote:
>
> From: "Liam R. Howlett" <liam.howl...@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.howl...@oracle.com>
> Signed-off-by: Vlastimil Babka <vba...@suse.cz>
> ---
> include/linux/maple_tree.h | 4 +++-
> lib/maple_tree.c | 47
> ++++++++++++++++++++++++++++++++++++++++------
> 2 files changed, 44 insertions(+), 7 deletions(-)
>
> diff --git a/include/linux/maple_tree.h b/include/linux/maple_tree.h
> index
> 3cf1ae9dde7ce43fa20ae400c01fefad048c302e..61eb5e7d09ad0133978e3ac4b2af66710421e769
> 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
> 3c3c14a76d98ded3b619c178d64099b464a2ca23..9aa782b1497f224e7366ebbd65f997523ee0c8ab
> 100644
> --- a/lib/maple_tree.c
> +++ b/lib/maple_tree.c
> @@ -1101,16 +1101,23 @@ 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;
> }
>
> @@ -1121,9 +1128,34 @@ 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;
> +
> + 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)) {
When would this condition happen? Do we really need to free mas->alloc
here or it can be reused for the next 1-node allocation?
> + mt_free_one(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;
> @@ -5386,8 +5418,11 @@ 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)
> + mt_free_one(mas->alloc);
> + mas->alloc = NULL;
> }
> EXPORT_SYMBOL_GPL(mas_destroy);
>
> @@ -6074,7 +6109,7 @@ 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;
>
> --
> 2.50.1
>
