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

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Message-ID: <20211215182818.ibsmvehcozznvgg5@revolver>
Date:   Wed, 15 Dec 2021 18:28:26 +0000
From:   Liam Howlett <liam.howlett@...cle.com>
To:     Vlastimil Babka <vbabka@...e.cz>
CC:     "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>,
        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}

* Vlastimil Babka <vbabka@...e.cz> [211215 11:43]:
> 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()

It is not needed with the mmap_lock() being used in the maple tree.  But
I should either be consistent and keep it everywhere or not have it in
the earlier patch.  I will fix this, maybe I should have left them in
everywhere.