[PATCH v2 0/2] Reduce the space to be cleared for maple_big_node

[PATCH v2 0/2] Reduce the space to be cleared for maple_big_node

[Wei Yang]

Found current code may clear maple_big_node redundantly.

First we define a filed parent, which is never used. After removing this, we
reduce the size of memory to be clear on memset.

Then mast_fill_bnode clear part of the structure twice, since slot and gap
shares some space. By clearing the whole structure, we can avoid it.

Wei Yang (2):
  maple_tree: remove maple_big_node.parent
  maple_tree: memset maple_big_node as a whole

 lib/maple_tree.c | 6 +-----
 1 file changed, 1 insertion(+), 5 deletions(-)

-- 
2.34.1

[PATCH v2 1/2] maple_tree: remove maple_big_node.parent

[Wei Yang]

The member parent of maple_big_node is never used.

Let's remove it which could reduce the number of space to be cleared on
memset.

Signed-off-by: Wei Yang <richard.weiyang@gmail.com>
CC: Liam R. Howlett <Liam.Howlett@Oracle.com>
---
 lib/maple_tree.c | 1 -
 1 file changed, 1 deletion(-)

diff --git a/lib/maple_tree.c b/lib/maple_tree.c
index 4e08dd5e391b..c3370c7449c2 100644
--- a/lib/maple_tree.c
+++ b/lib/maple_tree.c
@@ -120,7 +120,6 @@ static const unsigned char mt_min_slots[] = {
 #define MAPLE_BIG_NODE_GAPS	(MAPLE_ARANGE64_SLOTS * 2 + 1)
 
 struct maple_big_node {
-	struct maple_pnode *parent;
 	unsigned long pivot[MAPLE_BIG_NODE_SLOTS - 1];
 	union {
 		struct maple_enode *slot[MAPLE_BIG_NODE_SLOTS];
-- 
2.34.1

[PATCH v2 2/2] maple_tree: memset maple_big_node as a whole

[Wei Yang]

In function mast_fill_bnode(), we first clear some fields of
maple_big_node and set the 'type' unconditionally before return. This
means we won't leverage any information in maple_big_node and it is safe
to clear the whole structure.

In maple_big_node, we define slot and padding/gap in a union. And based
on current definition of MAPLE_BIG_NODE_SLOTS/GAPS, padding is always
less than slot and part of the gap is overlapped by slot.

For example on 64bit system:

  MAPLE_BIG_NODE_SLOT is 34
  MAPLE_BIG_NODE_GAP  is 21

With this knowledge, current code may clear some space by twice. And
this could be avoid by clearing the structure as a whole.

Signed-off-by: Wei Yang <richard.weiyang@gmail.com>
CC: Liam R. Howlett <Liam.Howlett@Oracle.com>

---
v2: correct the change log on clearing all maple_big_node currently
---
 lib/maple_tree.c | 5 +----
 1 file changed, 1 insertion(+), 4 deletions(-)

diff --git a/lib/maple_tree.c b/lib/maple_tree.c
index c3370c7449c2..b459fe1a3ebe 100644
--- a/lib/maple_tree.c
+++ b/lib/maple_tree.c
@@ -3134,10 +3134,7 @@ static inline void mast_fill_bnode(struct maple_subtree_state *mast,
 	bool cp = true;
 	unsigned char split;
 
-	memset(mast->bn->gap, 0, sizeof(unsigned long) * ARRAY_SIZE(mast->bn->gap));
-	memset(mast->bn->slot, 0, sizeof(unsigned long) * ARRAY_SIZE(mast->bn->slot));
-	memset(mast->bn->pivot, 0, sizeof(unsigned long) * ARRAY_SIZE(mast->bn->pivot));
-	mast->bn->b_end = 0;
+	memset(mast->bn, 0, sizeof(struct maple_big_node));
 
 	if (mte_is_root(mas->node)) {
 		cp = false;
-- 
2.34.1

Re: [PATCH v2 1/2] maple_tree: remove maple_big_node.parent

[Liam R. Howlett]

* Wei Yang <richard.weiyang@gmail.com> [240908 10:06]:
> The member parent of maple_big_node is never used.
> 
> Let's remove it which could reduce the number of space to be cleared on
> memset.
> 
> Signed-off-by: Wei Yang <richard.weiyang@gmail.com>
> CC: Liam R. Howlett <Liam.Howlett@Oracle.com>

Reviewed-by: Liam R. Howlett <Liam.Howlett@Oracle.com>

> ---
>  lib/maple_tree.c | 1 -
>  1 file changed, 1 deletion(-)
> 
> diff --git a/lib/maple_tree.c b/lib/maple_tree.c
> index 4e08dd5e391b..c3370c7449c2 100644
> --- a/lib/maple_tree.c
> +++ b/lib/maple_tree.c
> @@ -120,7 +120,6 @@ static const unsigned char mt_min_slots[] = {
>  #define MAPLE_BIG_NODE_GAPS	(MAPLE_ARANGE64_SLOTS * 2 + 1)
>  
>  struct maple_big_node {
> -	struct maple_pnode *parent;
>  	unsigned long pivot[MAPLE_BIG_NODE_SLOTS - 1];
>  	union {
>  		struct maple_enode *slot[MAPLE_BIG_NODE_SLOTS];
> -- 
> 2.34.1
> 

Re: [PATCH v2 2/2] maple_tree: memset maple_big_node as a whole

[Liam R. Howlett]

* Wei Yang <richard.weiyang@gmail.com> [240908 10:06]:
> In function mast_fill_bnode(), we first clear some fields of
> maple_big_node and set the 'type' unconditionally before return. This
> means we won't leverage any information in maple_big_node and it is safe
> to clear the whole structure.
> 
> In maple_big_node, we define slot and padding/gap in a union. And based
> on current definition of MAPLE_BIG_NODE_SLOTS/GAPS, padding is always
> less than slot and part of the gap is overlapped by slot.
> 
> For example on 64bit system:
> 
>   MAPLE_BIG_NODE_SLOT is 34
>   MAPLE_BIG_NODE_GAP  is 21
> 
> With this knowledge, current code may clear some space by twice. And
> this could be avoid by clearing the structure as a whole.
> 
> Signed-off-by: Wei Yang <richard.weiyang@gmail.com>
> CC: Liam R. Howlett <Liam.Howlett@Oracle.com>

Reviewed-by: Liam R. Howlett <Liam.Howlett@Oracle.com>

> 
> ---
> v2: correct the change log on clearing all maple_big_node currently

Thanks!

> ---
>  lib/maple_tree.c | 5 +----
>  1 file changed, 1 insertion(+), 4 deletions(-)
> 
> diff --git a/lib/maple_tree.c b/lib/maple_tree.c
> index c3370c7449c2..b459fe1a3ebe 100644
> --- a/lib/maple_tree.c
> +++ b/lib/maple_tree.c
> @@ -3134,10 +3134,7 @@ static inline void mast_fill_bnode(struct maple_subtree_state *mast,
>  	bool cp = true;
>  	unsigned char split;
>  
> -	memset(mast->bn->gap, 0, sizeof(unsigned long) * ARRAY_SIZE(mast->bn->gap));
> -	memset(mast->bn->slot, 0, sizeof(unsigned long) * ARRAY_SIZE(mast->bn->slot));
> -	memset(mast->bn->pivot, 0, sizeof(unsigned long) * ARRAY_SIZE(mast->bn->pivot));
> -	mast->bn->b_end = 0;
> +	memset(mast->bn, 0, sizeof(struct maple_big_node));
>  
>  	if (mte_is_root(mas->node)) {
>  		cp = false;
> -- 
> 2.34.1
> 

Re: [PATCH v2 0/2] Reduce the space to be cleared for maple_big_node

[Wei Yang]

Hi, Andrew,

I don't see the notification on picking this in unstable/stable.

May I ask would it be picked up?

On Sun, Sep 08, 2024 at 02:05:52PM +0000, Wei Yang wrote:
>Found current code may clear maple_big_node redundantly.
>
>First we define a filed parent, which is never used. After removing this, we
>reduce the size of memory to be clear on memset.
>
>Then mast_fill_bnode clear part of the structure twice, since slot and gap
>shares some space. By clearing the whole structure, we can avoid it.
>
>Wei Yang (2):
>  maple_tree: remove maple_big_node.parent
>  maple_tree: memset maple_big_node as a whole
>
> lib/maple_tree.c | 6 +-----
> 1 file changed, 1 insertion(+), 5 deletions(-)
>
>-- 
>2.34.1

-- 
Wei Yang
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