linux-kernel - Re: [PATCH v4 11/66] mm/mmap: Use maple tree for unmapped_area{

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Message-ID: <97b96d36-434e-fb4e-3e0f-7c96faa9cef9@suse.cz>
Date:   Wed, 15 Dec 2021 17:43:26 +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 11/66] mm/mmap: Use maple tree for
 unmapped_area{_topdown}

On 12/1/21 15:29, Liam Howlett wrote:
> From: "Liam R. Howlett" <Liam.Howlett@...cle.com>
> 
> The maple tree code was added to find the unmapped area in a previous
> commit and was checked against what the rbtree returned, but the actual
> result was never used.  Start using the maple tree implementation and
> remove the rbtree code.

Nice cleanup. But...

> Add kernel documentation comment for these functions.
> 
> Signed-off-by: Liam R. Howlett <Liam.Howlett@...cle.com>

>  
>  	/* Adjust search length to account for worst case alignment overhead */
>  	length = info->length + info->align_mask;
>  	if (length < info->length)
>  		return -ENOMEM;
>  
> -	rcu_read_lock();
> -	mas_empty_area_rev(&mas, info->low_limit, info->high_limit - 1,
> -			   length);
> -	rcu_read_unlock();

Why is RCU locking being removed as part of this? Ditton in
unmapped_area_topdown()