Re: [PATCH v2 08/10] maple_tree: Rework mas_wr_slot_store() to be cleaner and more efficient.

[Peng Zhang]

在 2023/5/18 06:48, Liam R. Howlett 写道:
> * Peng Zhang <zhangpeng.00@xxxxxxxxxxxxx> [230517 04:59]:
> > The code of mas_wr_slot_store() is messy, make it clearer and concise,
> > and add comments. In addition, get whether the two gaps are empty to
> > avoid calling mas_update_gap() all the time.
> >
> > Signed-off-by: Peng Zhang <zhangpeng.00@xxxxxxxxxxxxx>
> > ---
> >   lib/maple_tree.c | 59 ++++++++++++++++++++----------------------------
> >   1 file changed, 24 insertions(+), 35 deletions(-)
> >
> > diff --git a/lib/maple_tree.c b/lib/maple_tree.c
> > index bbe4c6f2858c..25a8b7d5d598 100644
> > --- a/lib/maple_tree.c
> > +++ b/lib/maple_tree.c
> > @@ -4200,49 +4200,38 @@ static inline bool mas_wr_node_store(struct ma_wr_state *wr_mas)
> >   static inline bool mas_wr_slot_store(struct ma_wr_state *wr_mas)
> >   {
> >   	struct ma_state *mas = wr_mas->mas;
> > -	unsigned long lmax; /* Logical max. */
> >   	unsigned char offset = mas->offset;
> > +	unsigned char offset_end = wr_mas->offset_end;
> > +	unsigned long lmax = wr_mas->end_piv; /* Logical max. */
> > +	bool gap = false;
> >   
> > -	if ((wr_mas->r_max > mas->last) && ((wr_mas->r_min != mas->index) ||
> > -				  (offset != wr_mas->node_end)))
> > +	if (offset_end - offset != 1)
> >   		return false;
> >   
> > -	if (offset == wr_mas->node_end - 1)
> > -		lmax = mas->max;
> > -	else
> > -		lmax = wr_mas->pivots[offset + 1];
> > -
> > -	/* going to overwrite too many slots. */
> > -	if (lmax < mas->last)
> > -		return false;
> > -
> > -	if (wr_mas->r_min == mas->index) {
> > -		/* overwriting two or more ranges with one. */
> > -		if (lmax == mas->last)
> > -			return false;
> > -
> > -		/* Overwriting all of offset and a portion of offset + 1. */
> > +	if (mas->index == wr_mas->r_min && mas->last < lmax) {
> > +		/* Overwriting the range and over a part of the next range. */
> > +		gap |= !mt_slot_locked(mas->tree, wr_mas->slots, offset);
> > +		gap |= !mt_slot_locked(mas->tree, wr_mas->slots, offset + 1);
> >   		rcu_assign_pointer(wr_mas->slots[offset], wr_mas->entry);
> >   		wr_mas->pivots[offset] = mas->last;
> > -		goto done;
> > -	}
> > -
> > -	/* Doesn't end on the next range end. */
> > -	if (lmax != mas->last)
> > +	} else if (mas->index > wr_mas->r_min && mas->last == lmax) {
> > +		/* Overwriting a part of the range and over the next range */
> > +		gap |= !mt_slot_locked(mas->tree, wr_mas->slots, offset);
> > +		gap |= !mt_slot_locked(mas->tree, wr_mas->slots, offset + 1);
> > +		rcu_assign_pointer(wr_mas->slots[offset + 1], wr_mas->entry);
> > +		wr_mas->pivots[offset] = mas->index - 1;
> > +		mas->offset++; /* Keep mas accurate. */
> > +	} else {
> >   		return false;
>
> Again here, I think you have already verified this will be a slot store
> by offset_end - offset == 1 and new_end == wr_mas->node_end.
>
> The checking of the slots for the gap could be moved outside the
> statements.  WDYT?
Yes, I'll address this in v3. Thanks.
> > +	}
> >   
> > -	/* Overwriting a portion of offset and all of offset + 1 */
> > -	if ((offset + 1 < mt_pivots[wr_mas->type]) &&
> > -	    (wr_mas->entry || wr_mas->pivots[offset + 1]))
> > -		wr_mas->pivots[offset + 1] = mas->last;
> > -
> > -	rcu_assign_pointer(wr_mas->slots[offset + 1], wr_mas->entry);
> > -	wr_mas->pivots[offset] = mas->index - 1;
> > -	mas->offset++; /* Keep mas accurate. */
> > -
> > -done:
> >   	trace_ma_write(__func__, mas, 0, wr_mas->entry);
> > -	mas_update_gap(mas);
> > +	/*
> > +	 * Only update gap when the new entry is empty or there is an empty
> > +	 * entry in the original two ranges.
> > +	 */
> > +	if (!wr_mas->entry || gap)
> > +		mas_update_gap(mas);
> >   	return true;
> >   }
> >   
> > @@ -4396,7 +4385,7 @@ static inline void mas_wr_modify(struct ma_wr_state *wr_mas)
> >   	if (new_end == wr_mas->node_end + 1 && mas_wr_append(wr_mas))
> >   		return;
> >   
> > -	if ((wr_mas->offset_end - mas->offset <= 1) && mas_wr_slot_store(wr_mas))
> > +	if (new_end == wr_mas->node_end && mas_wr_slot_store(wr_mas))
> >   		return;
> >   	else if (mas_wr_node_store(wr_mas))
> >   		return;
> > --
> > 2.20.1