linux-kernel - Re: [PATCH v5 14/14] maple_tree: Convert forking to use the sheaf interface

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Message-ID: <CAJuCfpH4PNCaMQ4k3iOvt7BK-+nDzVV1p3PcH++7DFGGvg9=fA@mail.gmail.com>
Date: Fri, 22 Aug 2025 13:29:14 -0700
From: Suren Baghdasaryan <surenb@...gle.com>
To: Vlastimil Babka <vbabka@...e.cz>
Cc: "Liam R. Howlett" <Liam.Howlett@...cle.com>, Christoph Lameter <cl@...two.org>, 
	David Rientjes <rientjes@...gle.com>, Roman Gushchin <roman.gushchin@...ux.dev>, 
	Harry Yoo <harry.yoo@...cle.com>, Uladzislau Rezki <urezki@...il.com>, linux-mm@...ck.org, 
	linux-kernel@...r.kernel.org, rcu@...r.kernel.org, 
	maple-tree@...ts.infradead.org
Subject: Re: [PATCH v5 14/14] maple_tree: Convert forking to use the sheaf interface

On Wed, Jul 23, 2025 at 6:35 AM Vlastimil Babka <vbabka@...e.cz> wrote:
>
> From: "Liam R. Howlett" <Liam.Howlett@...cle.com>
>
> Use the generic interface which should result in less bulk allocations
> during a forking.
>
> A part of this is to abstract the freeing of the sheaf or maple state
> allocations into its own function so mas_destroy() and the tree
> duplication code can use the same functionality to return any unused
> resources.
>
> Signed-off-by: Liam R. Howlett <Liam.Howlett@...cle.com>
> Signed-off-by: Vlastimil Babka <vbabka@...e.cz>

Reviewed-by: Suren Baghdasaryan <surenb@...gle.com>

> ---
>  lib/maple_tree.c | 42 +++++++++++++++++++++++-------------------
>  1 file changed, 23 insertions(+), 19 deletions(-)
>
> diff --git a/lib/maple_tree.c b/lib/maple_tree.c
> index 9aa782b1497f224e7366ebbd65f997523ee0c8ab..180d5e2ea49440248aaae04a066276406b2537ed 100644
> --- a/lib/maple_tree.c
> +++ b/lib/maple_tree.c
> @@ -1178,6 +1178,19 @@ static inline void mas_alloc_nodes(struct ma_state *mas, gfp_t gfp)
>         mas_set_err(mas, -ENOMEM);
>  }
>
> +static inline void mas_empty_nodes(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;
> +       }
> +}
>
>  /*
>   * mas_free() - Free an encoded maple node
> @@ -5414,15 +5427,7 @@ void mas_destroy(struct ma_state *mas)
>                 mas->mas_flags &= ~MA_STATE_REBALANCE;
>         }
>         mas->mas_flags &= ~(MA_STATE_BULK|MA_STATE_PREALLOC);
> -
> -       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;
> +       mas_empty_nodes(mas);
>  }
>  EXPORT_SYMBOL_GPL(mas_destroy);
>
> @@ -6499,7 +6504,7 @@ static inline void mas_dup_alloc(struct ma_state *mas, struct ma_state *new_mas,
>         struct maple_node *node = mte_to_node(mas->node);
>         struct maple_node *new_node = mte_to_node(new_mas->node);
>         enum maple_type type;
> -       unsigned char request, count, i;
> +       unsigned char count, i;
>         void __rcu **slots;
>         void __rcu **new_slots;
>         unsigned long val;
> @@ -6507,20 +6512,17 @@ static inline void mas_dup_alloc(struct ma_state *mas, struct ma_state *new_mas,
>         /* Allocate memory for child nodes. */
>         type = mte_node_type(mas->node);
>         new_slots = ma_slots(new_node, type);
> -       request = mas_data_end(mas) + 1;
> -       count = mt_alloc_bulk(gfp, request, (void **)new_slots);
> -       if (unlikely(count < request)) {
> -               memset(new_slots, 0, request * sizeof(void *));
> -               mas_set_err(mas, -ENOMEM);
> +       count = mas->node_request = mas_data_end(mas) + 1;
> +       mas_alloc_nodes(mas, gfp);
> +       if (unlikely(mas_is_err(mas)))
>                 return;
> -       }
>
> -       /* Restore node type information in slots. */
>         slots = ma_slots(node, type);
>         for (i = 0; i < count; i++) {
>                 val = (unsigned long)mt_slot_locked(mas->tree, slots, i);
>                 val &= MAPLE_NODE_MASK;
> -               ((unsigned long *)new_slots)[i] |= val;
> +               new_slots[i] = ma_mnode_ptr((unsigned long)mas_pop_node(mas) |
> +                                           val);
>         }
>  }
>
> @@ -6574,7 +6576,7 @@ static inline void mas_dup_build(struct ma_state *mas, struct ma_state *new_mas,
>                         /* Only allocate child nodes for non-leaf nodes. */
>                         mas_dup_alloc(mas, new_mas, gfp);
>                         if (unlikely(mas_is_err(mas)))
> -                               return;
> +                               goto empty_mas;
>                 } else {
>                         /*
>                          * This is the last leaf node and duplication is
> @@ -6607,6 +6609,8 @@ static inline void mas_dup_build(struct ma_state *mas, struct ma_state *new_mas,
>         /* Make them the same height */
>         new_mas->tree->ma_flags = mas->tree->ma_flags;
>         rcu_assign_pointer(new_mas->tree->ma_root, root);
> +empty_mas:
> +       mas_empty_nodes(mas);
>  }
>
>  /**
>
> --
> 2.50.1
>