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Arunpravin Paneer Selvam 1b339b19ee drm/buddy: Optimize free block management with RB tree 
commit c178e534ff upstream.

Replace the freelist (O(n)) used for free block management with a
red-black tree, providing more efficient O(log n) search, insert,
and delete operations. This improves scalability and performance
when managing large numbers of free blocks per order (e.g., hundreds
or thousands).

In the VK-CTS memory stress subtest, the buddy manager merges
fragmented memory and inserts freed blocks into the freelist. Since
freelist insertion is O(n), this becomes a bottleneck as fragmentation
increases. Benchmarking shows list_insert_sorted() consumes ~52.69% CPU
with the freelist, compared to just 0.03% with the RB tree
(rbtree_insert.isra.0), despite performing the same sorted insert.

This also improves performance in heavily fragmented workloads,
such as games or graphics tests that stress memory.

As the buddy allocator evolves with new features such as clear-page
tracking, the resulting fragmentation and complexity have grown.
These RB-tree based design changes are introduced to address that
growth and ensure the allocator continues to perform efficiently
under fragmented conditions.

The RB tree implementation with separate clear/dirty trees provides:
- O(n log n) aggregate complexity for all operations instead of O(n^2)
- Elimination of soft lockups and system instability
- Improved code maintainability and clarity
- Better scalability for large memory systems
- Predictable performance under fragmentation

v3(Matthew):
  - Remove RB_EMPTY_NODE check in force_merge function.
  - Rename rb for loop macros to have less generic names and move to
    .c file.
  - Make the rb node rb and link field as union.

v4(Jani Nikula):
  - The kernel-doc comment should be "/**"
  - Move all the rbtree macros to rbtree.h and add parens to ensure
    correct precedence.

v5:
  - Remove the inline in a .c file (Jani Nikula).

v6(Peter Zijlstra):
  - Add rb_add() function replacing the existing rbtree_insert() code.

v7:
  - A full walk iteration in rbtree is slower than the list (Peter Zijlstra).
  - The existing rbtree_postorder_for_each_entry_safe macro should be used
    in scenarios where traversal order is not a critical factor (Christian).

v8(Matthew):
  - Remove the rbtree_is_empty() check in this patch as well.

Cc: stable@vger.kernel.org
Fixes: a68c7eaa7a ("drm/amdgpu: Enable clear page functionality")
Signed-off-by: Arunpravin Paneer Selvam <Arunpravin.PaneerSelvam@amd.com>
Reviewed-by: Matthew Auld <matthew.auld@intel.com>
Link: https://lore.kernel.org/r/20251006095124.1663-1-Arunpravin.PaneerSelvam@amd.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
History 2026-01-08 10:14:52 +01:00
arch LoongArch: BPF: Sign extend kfunc call arguments 2026-01-08 10:14:51 +01:00
block
certs
crypto
Documentation dt-bindings: PCI: qcom,pcie-sm8550: Add missing required power-domains and resets 2026-01-08 10:14:28 +01:00
drivers
fs nfsd: Drop the client reference in client_states_open() 2026-01-08 10:14:51 +01:00
include
init
io_uring
ipc ipc: fix to protect IPCS lookups using RCU 2025-06-27 11:11:22 +01:00
kernel
lib idr: fix idr_alloc() returning an ID out of range 2026-01-08 10:14:50 +01:00
LICENSES
mm
net
rust
samples samples/ftrace: Adjust LoongArch register restore order in direct calls 2026-01-08 10:14:50 +01:00
scripts
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usr
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.clang-format clang-format: Update with v6.11-rc1's for_each macro list 2024-08-02 13:20:31 +02:00
.clippy.toml
.cocciconfig
.editorconfig .editorconfig: remove trim_trailing_whitespace option 2024-06-13 16:47:52 +02:00
.get_maintainer.ignore Add Jeff Kirsher to .get_maintainer.ignore 2024-03-08 11:36:54 +00:00
.gitattributes
.gitignore rust: introduce .clippy.toml 2025-03-13 13:01:42 +01:00
.mailmap
.rustfmt.toml
COPYING COPYING: state that all contributions really are covered by this file 2020-02-10 13:32:20 -08:00
CREDITS MAINTAINERS: Remove self from DSA entry 2024-11-03 12:52:38 -08:00
Kbuild
Kconfig kbuild: ensure full rebuild when the compiler is updated 2020-05-12 13:28:33 +09:00
MAINTAINERS staging: rtl8712: Remove driver using deprecated API wext 2025-12-07 06:25:02 +09:00
Makefile
README

README 

Linux kernel
============

There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.

In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``.  The formatted documentation can also be read online at:

    https://www.kernel.org/doc/html/latest/

There are various text files in the Documentation/ subdirectory,
several of them using the reStructuredText markup notation.

Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.