linux-kernel - Re: [PATCH v4 04/17] maple_tree: introduce mas_wr_store

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Message-ID: <20240925020431.joykmu4zzahoglcl@master>
Date: Wed, 25 Sep 2024 02:04:31 +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 04/17] maple_tree: introduce mas_wr_store_type()

On Wed, Aug 14, 2024 at 12:19:31PM -0400, Sidhartha Kumar wrote:

Sorry for a late reply, I just see this change.

>+
>+/*
>+ * mas_wr_store_type() - Set the store type for a given
>+ * store operation.
>+ * @wr_mas: The maple write state
>+ */
>+static inline void mas_wr_store_type(struct ma_wr_state *wr_mas)
>+{
>+	struct ma_state *mas = wr_mas->mas;
>+	unsigned char new_end;
>+
>+	if (unlikely(mas_is_none(mas) || mas_is_ptr(mas))) {
>+		mas->store_type = wr_store_root;
>+		return;
>+	}
>+
>+	if (unlikely(!mas_wr_walk(wr_mas))) {
>+		mas->store_type = wr_spanning_store;
>+		return;
>+	}
>+
>+	/* At this point, we are at the leaf node that needs to be altered. */
>+	mas_wr_end_piv(wr_mas);
>+	if (!wr_mas->entry)
>+		mas_wr_extend_null(wr_mas);
>+
>+	new_end = mas_wr_new_end(wr_mas);
>+	if ((wr_mas->r_min == mas->index) && (wr_mas->r_max == mas->last)) {
>+		mas->store_type = wr_exact_fit;
>+		return;
>+	}
>+
>+	if (unlikely(!mas->index && mas->last == ULONG_MAX)) {
>+		mas->store_type = wr_new_root;
>+		return;
>+	}
>+
>+	/* Potential spanning rebalance collapsing a node */
>+	if (new_end < mt_min_slots[wr_mas->type]) {
>+		if (!mte_is_root(mas->node)) {
>+			mas->store_type = wr_rebalance;
>+			return;
>+		}
>+		mas->store_type = wr_node_store;
>+		return;
>+	}

After this check, we are sure new_end >= mt_min_slots[wr_mas->type].

>+
>+	if (new_end >= mt_slots[wr_mas->type]) {
>+		mas->store_type = wr_split_store;
>+		return;
>+	}
>+
>+	if (!mt_in_rcu(mas->tree) && (mas->offset == mas->end)) {
>+		mas->store_type = wr_append;
>+		return;
>+	}
>+
>+	if ((new_end == mas->end) && (!mt_in_rcu(mas->tree) ||
>+		(wr_mas->offset_end - mas->offset == 1))) {
>+		mas->store_type = wr_slot_store;
>+		return;
>+	}
>+
>+	if (mte_is_root(mas->node) || (new_end >= mt_min_slots[wr_mas->type]) ||
>+		(mas->mas_flags & MA_STATE_BULK)) {

The check (new_end >= mt_min_slots[wr_mas->type]) here seems always be true.

So the if here seems not necessary. Do I miss something?

>+		mas->store_type = wr_node_store;
>+		return;
>+	}
>+
>+	mas->store_type = wr_invalid;
>+	MAS_WARN_ON(mas, 1);
>+}
>+

-- 
Wei Yang
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