linux-kernel - Re: [PATCH v4 16/17] maple_tree: remove unneeded mas_wr_walk() in mas_store

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Message-ID: <20241024012038.zf3dpqsflnyi4wce@master>
Date: Thu, 24 Oct 2024 01:20:38 +0000
From: Wei Yang <richard.weiyang@...il.com>
To: Sidhartha Kumar <sidhartha.kumar@...cle.com>
Cc: linux-kernel@...r.kernel.org, maple-tree@...ts.infradead.org,
	linux-mm@...ck.org, akpm@...ux-foundation.org,
	liam.howlett@...cle.com, willy@...radead.org, surenb@...gle.com
Subject: Re: [PATCH v4 16/17] maple_tree: remove unneeded mas_wr_walk() in
 mas_store_prealloc()

On Wed, Aug 14, 2024 at 12:19:43PM -0400, Sidhartha Kumar wrote:
>Users of mas_store_prealloc() enter this function with nodes already
>preallocated. This means the store type must be already set. We can then
>remove the call to mas_wr_store_type() and initialize the write state to
>continue the partial walk that was done when determining the store type.
>

May I ask what is the partial walk here means?

It is the mas_wr_walk() in mas_wr_store_type() which is stopped because of it
is spanning write?

I may lost some background, so the assumption here is mas_wr_store_type() has
already been invoked and the store type has been decided, right?

>Reviewed-by: Liam R. Howlett <Liam.Howlett@...cle.com>
>Signed-off-by: Sidhartha Kumar <sidhartha.kumar@...cle.com>
>---
> lib/maple_tree.c | 18 +++++++++++++-----
> 1 file changed, 13 insertions(+), 5 deletions(-)
>
>diff --git a/lib/maple_tree.c b/lib/maple_tree.c
>index 8c1a1a483395..73ce63d9c3a0 100644
>--- a/lib/maple_tree.c
>+++ b/lib/maple_tree.c
>@@ -3979,9 +3979,6 @@ static inline void mas_wr_end_piv(struct ma_wr_state *wr_mas)
> 		wr_mas->end_piv = wr_mas->pivots[wr_mas->offset_end];
> 	else
> 		wr_mas->end_piv = wr_mas->mas->max;
>-
>-	if (!wr_mas->entry)
>-		mas_wr_extend_null(wr_mas);
> }
> 
> static inline unsigned char mas_wr_new_end(struct ma_wr_state *wr_mas)
>@@ -5532,8 +5529,19 @@ void mas_store_prealloc(struct ma_state *mas, void *entry)
> {
> 	MA_WR_STATE(wr_mas, mas, entry);
> 
>-	mas_wr_prealloc_setup(&wr_mas);
>-	mas_wr_store_type(&wr_mas);
>+	if (mas->store_type == wr_store_root) {
>+		mas_wr_prealloc_setup(&wr_mas);
>+		goto store;
>+	}
>+
>+	mas_wr_walk_descend(&wr_mas);

This one does not descend the tree, just locate the offset in a node and
adjust min/max. So not look like to continue the partial walk to me.

>+	if (mas->store_type != wr_spanning_store) {
>+		/* set wr_mas->content to current slot */
>+		wr_mas.content = mas_slot_locked(mas, wr_mas.slots, mas->offset);
>+		mas_wr_end_piv(&wr_mas);

If not a spanning write, the previous walk should reach a leaf node, right?

I am not sure why we don't need to check extend null here. Because we have
already done it?

>+	}
>+
>+store:
> 	trace_ma_write(__func__, mas, 0, entry);
> 	mas_wr_store_entry(&wr_mas);
> 	MAS_WR_BUG_ON(&wr_mas, mas_is_err(mas));
>-- 
>2.46.0
>

-- 
Wei Yang
Help you, Help me