Re: [PATCH 10/10] maple_tree: Simplify and clean up mas_wr_node_store()

[Peng Zhang]

在 2023/5/16 02:58, Liam R. Howlett 写道:
> * Peng Zhang <zhangpeng.00@xxxxxxxxxxxxx> [230515 09:18]:
> > Simplify and clean up mas_wr_node_store(), remove unnecessary code.
>
> This change fails the userspace testing for me.
>
> > Signed-off-by: Peng Zhang <zhangpeng.00@xxxxxxxxxxxxx>
> > ---
> >   lib/maple_tree.c | 75 +++++++++++++-----------------------------------
> >   1 file changed, 20 insertions(+), 55 deletions(-)
> >
> > diff --git a/lib/maple_tree.c b/lib/maple_tree.c
> > index d558e7bcb6da8..ff4aa01cf88b6 100644
> > --- a/lib/maple_tree.c
> > +++ b/lib/maple_tree.c
> > @@ -4066,46 +4066,21 @@ static inline int mas_wr_spanning_store(struct ma_wr_state *wr_mas)
> >    *
> >    * Return: True if stored, false otherwise
> >    */
> > -static inline bool mas_wr_node_store(struct ma_wr_state *wr_mas)
> > +static inline bool mas_wr_node_store(struct ma_wr_state *wr_mas,
> > +				     unsigned char new_end)
> >   {
> >   	struct ma_state *mas = wr_mas->mas;
> >   	void __rcu **dst_slots;
> >   	unsigned long *dst_pivots;
> >   	unsigned char dst_offset;
> > -	unsigned char new_end = wr_mas->node_end;
> > -	unsigned char offset;
> > -	unsigned char node_slots = mt_slots[wr_mas->type];
> >   	struct maple_node reuse, *newnode;
> > -	unsigned char copy_size, max_piv = mt_pivots[wr_mas->type];
> > +	unsigned char copy_size, node_pivots = mt_pivots[wr_mas->type];
> >   	bool in_rcu = mt_in_rcu(mas->tree);
> >   
> > -	offset = mas->offset;
> > -	if (mas->last == wr_mas->r_max) {
> > -		/* runs right to the end of the node */
> > -		if (mas->last == mas->max)
> > -			new_end = offset;
> > -		/* don't copy this offset */
> > +	if (mas->last == wr_mas->end_piv)
> >   		wr_mas->offset_end++;
I guess there is a problem here? If we modify wr_mas->offset_end,
but this function fails to try the fast path, it will enter the
slow path with the modified offset_end. But it also has this
problem in the previous version.

I applied this patch to linux-next/master but it passed the
userspace tests. I need more information to confirm what the
problem is.

Thanks.

> > -	} else if (mas->last < wr_mas->r_max) {
> > -		/* new range ends in this range */
> > -		if (unlikely(wr_mas->r_max == ULONG_MAX))
> > -			mas_bulk_rebalance(mas, wr_mas->node_end, wr_mas->type);
> > -
> > -		new_end++;
> > -	} else {
> > -		if (wr_mas->end_piv == mas->last)
> > -			wr_mas->offset_end++;
> > -
> > -		new_end -= wr_mas->offset_end - offset - 1;
> > -	}
> > -
> > -	/* new range starts within a range */
> > -	if (wr_mas->r_min < mas->index)
> > -		new_end++;
> > -
> > -	/* Not enough room */
> > -	if (new_end >= node_slots)
> > -		return false;
> > +	else if (unlikely(wr_mas->r_max == ULONG_MAX))
> > +		mas_bulk_rebalance(mas, wr_mas->node_end, wr_mas->type);
> >   
> >   	/* Not enough data. */
> >   	if (!mte_is_root(mas->node) && (new_end <= mt_min_slots[wr_mas->type]) &&
> > @@ -4128,47 +4103,36 @@ static inline bool mas_wr_node_store(struct ma_wr_state *wr_mas)
> >   	dst_pivots = ma_pivots(newnode, wr_mas->type);
> >   	dst_slots = ma_slots(newnode, wr_mas->type);
> >   	/* Copy from start to insert point */
> > -	memcpy(dst_pivots, wr_mas->pivots, sizeof(unsigned long) * (offset + 1));
> > -	memcpy(dst_slots, wr_mas->slots, sizeof(void *) * (offset + 1));
> > -	dst_offset = offset;
> > +	memcpy(dst_pivots, wr_mas->pivots, sizeof(unsigned long) * mas->offset);
> > +	memcpy(dst_slots, wr_mas->slots, sizeof(void *) * mas->offset);
> >   
> >   	/* Handle insert of new range starting after old range */
> >   	if (wr_mas->r_min < mas->index) {
> > -		mas->offset++;
> > -		rcu_assign_pointer(dst_slots[dst_offset], wr_mas->content);
> > -		dst_pivots[dst_offset++] = mas->index - 1;
> > +		rcu_assign_pointer(dst_slots[mas->offset], wr_mas->content);
> > +		dst_pivots[mas->offset++] = mas->index - 1;
> >   	}
> >   
> >   	/* Store the new entry and range end. */
> > -	if (dst_offset < max_piv)
> > -		dst_pivots[dst_offset] = mas->last;
> > -	mas->offset = dst_offset;
> > -	rcu_assign_pointer(dst_slots[dst_offset], wr_mas->entry);
> > +	if (mas->offset < node_pivots)
> > +		dst_pivots[mas->offset] = mas->last;
> > +	rcu_assign_pointer(dst_slots[mas->offset], wr_mas->entry);
> >   
> >   	/*
> >   	 * this range wrote to the end of the node or it overwrote the rest of
> >   	 * the data
> >   	 */
> > -	if (wr_mas->offset_end > wr_mas->node_end || mas->last >= mas->max) {
> > -		new_end = dst_offset;
> > +	if (wr_mas->offset_end > wr_mas->node_end)
> >   		goto done;
> > -	}
> >   
> > -	dst_offset++;
> > +	dst_offset = mas->offset + 1;
> >   	/* Copy to the end of node if necessary. */
> >   	copy_size = wr_mas->node_end - wr_mas->offset_end + 1;
> >   	memcpy(dst_slots + dst_offset, wr_mas->slots + wr_mas->offset_end,
> >   	       sizeof(void *) * copy_size);
> > -	if (dst_offset < max_piv) {
> > -		if (copy_size > max_piv - dst_offset)
> > -			copy_size = max_piv - dst_offset;
> > +	memcpy(dst_pivots + dst_offset, wr_mas->pivots + wr_mas->offset_end,
> > +	       sizeof(unsigned long) * (copy_size - 1));
> >   
> > -		memcpy(dst_pivots + dst_offset,
> > -		       wr_mas->pivots + wr_mas->offset_end,
> > -		       sizeof(unsigned long) * copy_size);
> > -	}
> > -
> > -	if ((wr_mas->node_end == node_slots - 1) && (new_end < node_slots - 1))
> > +	if (new_end < node_pivots)
> >   		dst_pivots[new_end] = mas->max;
> >   
> >   done:
> > @@ -4429,7 +4393,8 @@ static inline void mas_wr_modify(struct ma_wr_state *wr_mas)
> >   
> >   	if (new_end == wr_mas->node_end && mas_wr_slot_store(wr_mas))
> >   		return;
> > -	else if (mas_wr_node_store(wr_mas))
> > +
> > +	if (mas_wr_node_store(wr_mas, new_end))
> >   		return;
> >   
> >   	if (mas_is_err(mas))
> > --
> > 2.20.1