linux-kernel - Re: [PATCH v8 00/70] Introducing the Maple Tree

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Message-Id: <20220426130857.09f40743b42b5f0bf4f19a59@linux-foundation.org>
Date:   Tue, 26 Apr 2022 13:08:57 -0700
From:   Andrew Morton <akpm@...ux-foundation.org>
To:     Liam Howlett <liam.howlett@...cle.com>
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>,
        Yu Zhao <yuzhao@...gle.com>
Subject: Re: [PATCH v8 00/70] Introducing the Maple Tree

On Tue, 26 Apr 2022 15:06:19 +0000 Liam Howlett <liam.howlett@...cle.com> wrote:

> The maple tree is an RCU-safe range based B-tree designed to use modern
> processor cache efficiently.  There are a number of places in the kernel

I think it would be helpful to expand on "a number of places". 
Specifically which places?

> that a non-overlapping range-based tree would be beneficial, especially
> one with a simple interface.  The first user that is covered in this
> patch set is the vm_area_struct, where three data structures are
> replaced by the maple tree: the augmented rbtree, the vma cache, and the
> linked list of VMAs in the mm_struct.  The long term goal is to reduce
> or remove the mmap_sem contention.

"mmap_lock" ;)

> 
> The tree has a branching factor of 10 for non-leaf nodes and 16 for leaf
> nodes.  With the increased branching factor, it is significantly shorter than
> the rbtree so it has fewer cache misses.  The removal of the linked list
> between subsequent entries also reduces the cache misses and the need to pull
> in the previous and next VMA during many tree alterations.

Do we have any quantitative testing results?

What's the plan on utilizing this to further reduce mmap_lock contention?