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Date: Thu, 13 Jun 2024 11:00:57 -0400
From: "Liam R. Howlett" <Liam.Howlett@oracle.com>
To: Sidhartha Kumar <sidhartha.kumar@oracle.com>
Cc: linux-kernel@vger.kernel.org, maple-tree@lists.infradead.org,
        linux-mm@kvack.org, akpm@linux-foundation.org, willy@infradead.org
Subject: Re: [PATCH v2 13/16] maple_tree: have mas_store() allocate nodes if
 needed
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 <20240607185257.963768-14-sidhartha.kumar@oracle.com>
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* Sidhartha Kumar <sidhartha.kumar@oracle.com> [240607 14:53]:
> Not all users of mas_store() enter with nodes already preallocated.
> Check for the MA_STATE_PREALLOC flag to decide whether to preallocate nodes
> within mas_store() rather than relying on future write helper functions
> to perform the allocations. This allows the write helper functions to be
> simplified as they do not have to do checks to make sure there are
> enough allocated nodes to perform the write.
> 
> Signed-off-by: Sidhartha Kumar <sidhartha.kumar@oracle.com>
> ---
>  lib/maple_tree.c | 32 ++++++++++++++++++++++++++++----
>  1 file changed, 28 insertions(+), 4 deletions(-)
> 
> diff --git a/lib/maple_tree.c b/lib/maple_tree.c
> index 8b17768db5f2..92f133ea5f00 100644
> --- a/lib/maple_tree.c
> +++ b/lib/maple_tree.c
> @@ -5528,6 +5528,20 @@ static inline void mte_destroy_walk(struct maple_enode *enode,
>  		mt_destroy_walk(enode, mt, true);
>  	}
>  }
> +
> +static inline void mas_wr_store_prealloc(struct ma_wr_state *wr_mas, void *entry)
> +{
> +	struct ma_state *mas = wr_mas->mas;
> +	int request;
> +
> +	mas_wr_prealloc_setup(wr_mas);
> +	mas_wr_store_type(wr_mas);
> +	request = mas_prealloc_calc(mas, entry);
> +	if (!request)
> +		return;
> +
> +	mas_node_count(mas, request);
> +}
>  /* Interface */
>  
>  /**
> @@ -5536,8 +5550,6 @@ static inline void mte_destroy_walk(struct maple_enode *enode,
>   * @entry: The entry to store.
>   *
>   * The @mas->index and @mas->last is used to set the range for the @entry.
> - * Note: The @mas should have pre-allocated entries to ensure there is memory to
> - * store the entry.  Please see mas_expected_entries()/mas_destroy() for more details.
>   *
>   * Return: the first entry between mas->index and mas->last or %NULL.
>   */
> @@ -5563,9 +5575,21 @@ void *mas_store(struct ma_state *mas, void *entry)
>  	 * want to examine what happens if a single store operation was to
>  	 * overwrite multiple entries within a self-balancing B-Tree.
>  	 */
> -	mas_wr_prealloc_setup(&wr_mas);
> -	mas_wr_store_type(&wr_mas);
> +	if (mas->mas_flags & MA_STATE_PREALLOC) {
> +		mas_wr_prealloc_setup(&wr_mas);
> +		mas_wr_store_type(&wr_mas);
> +		mas_wr_store_entry(&wr_mas);
> +		MAS_WR_BUG_ON(&wr_mas, mas_is_err(mas));
> +		return wr_mas.content;
> +	}
> +
> +	mas_wr_store_prealloc(&wr_mas, entry);

Since this is the only place mas_wr_store_prealloc() is called and the
first two things it does is the same as the if() statement above, then
both calls can be moved outside of the if() statement.  That also means
the helper function is somewhat small, which makes it seem like it's
probably not worth having?  Maybe I missed something though?

> +	WARN_ON_ONCE(mas->store_type == wr_invalid);
> +	if (mas_is_err(mas))
> +		return NULL;
> +
>  	mas_wr_store_entry(&wr_mas);
> +	mas_destroy(mas);
>  	return wr_mas.content;
>  }
>  EXPORT_SYMBOL_GPL(mas_store);
> -- 
> 2.45.2
>