linux-kernel - Re: [PATCH v4 05/66] Maple Tree: Add new data structure

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Date:   Wed, 15 Dec 2021 13:54:45 +0100
From:   Vlastimil Babka <vbabka@...e.cz>
To:     Liam Howlett <liam.howlett@...cle.com>,
        "maple-tree@...ts.infradead.org" <maple-tree@...ts.infradead.org>,
        "linux-mm@...ck.org" <linux-mm@...ck.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Andrew Morton <akpm@...ux-foundation.org>
Cc:     Song Liu <songliubraving@...com>,
        Davidlohr Bueso <dave@...olabs.net>,
        "Paul E . McKenney" <paulmck@...nel.org>,
        Matthew Wilcox <willy@...radead.org>,
        Laurent Dufour <ldufour@...ux.ibm.com>,
        David Rientjes <rientjes@...gle.com>,
        Axel Rasmussen <axelrasmussen@...gle.com>,
        Suren Baghdasaryan <surenb@...gle.com>,
        Rik van Riel <riel@...riel.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Michel Lespinasse <walken.cr@...il.com>,
        Jerome Glisse <jglisse@...hat.com>,
        Minchan Kim <minchan@...gle.com>,
        Joel Fernandes <joelaf@...gle.com>,
        Rom Lemarchand <romlem@...gle.com>
Subject: Re: [PATCH v4 05/66] Maple Tree: Add new data structure

On 12/1/21 15:29, Liam Howlett wrote:
> +/*
> + * mt_find() - Search from the start up until an entry is found.
> + * @mt: The maple tree
> + * @*index: Pointer which contains the start location of the search
> + * @max: The maximum value to check
> + *
> + * Handles locking.
> + *
> + * Return: The entry at or after the @*index or %NULL

Noticed later that the comment doesn't say how *index is updated.

> + */
> +void *mt_find(struct maple_tree *mt, unsigned long *index, unsigned long max)
> +{
> +	MA_STATE(mas, mt, *index, *index);
> +	void *entry;
> +#ifdef CONFIG_DEBUG_MAPLE_TREE
> +	unsigned long copy = *index;
> +#endif
> +
> +	trace_ma_read(__func__, &mas);
> +
> +	if ((*index) > max)
> +		return NULL;
> +
> +	rcu_read_lock();
> +retry:
> +	entry = mas_state_walk(&mas);
> +	if (mas_is_start(&mas))
> +		goto retry;
> +
> +	if (unlikely(xa_is_zero(entry)))
> +		entry = NULL;
> +
> +	if (entry)
> +		goto unlock;
> +
> +	while (mas_searchable(&mas) && (mas.index < max)) {
> +		entry = mas_next_entry(&mas, max);
> +		if (likely(entry && !xa_is_zero(entry)))
> +			break;
> +	}
> +
> +	if (unlikely(xa_is_zero(entry)))
> +		entry = NULL;
> +unlock:
> +	rcu_read_unlock();
> +	if (likely(entry)) {
> +		*index = mas.last + 1;
> +#ifdef CONFIG_DEBUG_MAPLE_TREE
> +		if ((*index) && (*index) <= copy)
> +			printk("index not increased! %lx <= %lx\n",
> +			       *index, copy);
> +		MT_BUG_ON(mt, (*index) && ((*index) <= copy));
> +#endif
> +	}
> +
> +	return entry;
> +}
> +EXPORT_SYMBOL(mt_find);