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

From: Andrew Morton
Date: Tue Apr 26 2022 - 16:09:15 EST

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