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Date: Sun, 14 Jun 2026 00:15:28 +0100
From: Matthew Wilcox <willy@infradead.org>
To: Pranjal Arya <pranjal.arya@oss.qualcomm.com>
Cc: Andrew Morton <akpm@linux-foundation.org>,
	Uladzislau Rezki <urezki@gmail.com>,
	"Liam R. Howlett" <liam@infradead.org>,
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	linux-kernel@vger.kernel.org, maple-tree@lists.infradead.org,
	Lorenzo Stoakes <ljs@kernel.org>,
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	Sudeep Holla <sudeep.holla@kernel.org>
Subject: Re: [PATCH RFC 00/12] mm/vmalloc: migrate vmap_area indexing from
 rb-tree to maple-tree
Message-ID: <ai3kkIpaR0aT_6q5@casper.infradead.org>
References: <20260613-vmalloc_maple-v1-0-0aa740bb944b@oss.qualcomm.com>
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In-Reply-To: <20260613-vmalloc_maple-v1-0-0aa740bb944b@oss.qualcomm.com>

On Sat, Jun 13, 2026 at 10:49:42PM +0530, Pranjal Arya wrote:
> vmalloc's free/busy/lazy area tracking is one of the last remaining
> augmented-rb_tree consumers in the core mm allocators. The rest of
> mm/ has been gradually consolidating range-keyed indexing around
> maple_tree (notably the per-process VMA tree in mm/mmap.c), and
> the underlying reason is a structural mismatch between rb_tree and
> range tracking:

First, and most importantly, I love this.  The maple tree is undoubtedly
the right data structure to use for this purpose.

What I don't understand is why you maintain a separate "free" tree.
It should not be necessary any more, but maybe you tried removing it
already and found a performance problem?