linux-kernel - Re: [PATCH v5 07/70] Maple Tree: Add new data structure

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Date:   Thu, 3 Feb 2022 16:02:43 +0000
From:   Mark Hemment <markhemm@...glemail.com>
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>,
        Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH v5 07/70] Maple Tree: Add new data structure

On Wed, 2 Feb 2022 at 02:42, Liam Howlett <liam.howlett@...cle.com> wrote:
>
> From: "Liam R. Howlett" <Liam.Howlett@...cle.com>
>
> 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
> 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.
>
> 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.
>
> Signed-off-by: Matthew Wilcox (Oracle) <willy@...radead.org>
> Signed-off-by: Liam R. Howlett <Liam.Howlett@...cle.com>
> ---
>  Documentation/core-api/index.rst              |    1 +
>  Documentation/core-api/maple_tree.rst         |  196 +
>  MAINTAINERS                                   |   12 +
>  include/linux/maple_tree.h                    |  673 ++
>  include/trace/events/maple_tree.h             |  123 +
>  lib/Kconfig.debug                             |    9 +
>  lib/Makefile                                  |    3 +-
>  lib/maple_tree.c                              | 6943 +++++++++++++++++
>  tools/testing/radix-tree/.gitignore           |    2 +
>  tools/testing/radix-tree/Makefile             |   13 +-
>  tools/testing/radix-tree/generated/autoconf.h |    1 +
>  tools/testing/radix-tree/linux/maple_tree.h   |    7 +
>  tools/testing/radix-tree/maple.c              |   59 +
>  .../radix-tree/trace/events/maple_tree.h      |    3 +
>  14 files changed, 8042 insertions(+), 3 deletions(-)
>  create mode 100644 Documentation/core-api/maple_tree.rst
>  create mode 100644 include/linux/maple_tree.h
>  create mode 100644 include/trace/events/maple_tree.h
>  create mode 100644 lib/maple_tree.c
>  create mode 100644 tools/testing/radix-tree/linux/maple_tree.h
>  create mode 100644 tools/testing/radix-tree/maple.c
>  create mode 100644 tools/testing/radix-tree/trace/events/maple_tree.h

...
> +Allocating Nodes
> +----------------
> +
> +Allocations are usually handled internally to the tree, however if allocations
> +need to occur before a write occurs then calling mas_entry_count() will
> +allocate the worst-case number of needed nodes to insert the provided number of
> +ranges.  This also causes the tree to enter mass insertion mode.  Once
> +insertions are complete calling mas_destroy() on the maple state will free the
> +unused allocations.

mas_entry_count() has been renamed to mas_expected_entries().
(Note: test code is still using mas_entry_count()).

Cheers,
Mark