Minki/linux
1
0
Fork 1
mirror of https://github.com/torvalds/linux.git synced 2024-10-23 05:30:55 +00:00
Code Issues Packages Projects Releases Wiki Activity
A mirror of the official Linux kernel repository just in case
1,279,374 Commits 7 Branches 858 Tags 7 GiB
C 97.6%
Assembly 1%
Shell 0.5%
Python 0.3%
Makefile 0.3%
ad59baa316
Go to file
Vlastimil Babka ad59baa316 slab, rust: extend kmalloc() alignment guarantees to remove Rust padding 
Slab allocators have been guaranteeing natural alignment for
power-of-two sizes since commit 59bb47985c ("mm, sl[aou]b: guarantee
natural alignment for kmalloc(power-of-two)"), while any other sizes are
guaranteed to be aligned only to ARCH_KMALLOC_MINALIGN bytes (although
in practice are aligned more than that in non-debug scenarios).

Rust's allocator API specifies size and alignment per allocation, which
have to satisfy the following rules, per Alice Ryhl [1]:

  1. The alignment is a power of two.
  2. The size is non-zero.
  3. When you round up the size to the next multiple of the alignment,
     then it must not overflow the signed type isize / ssize_t.

In order to map this to kmalloc()'s guarantees, some requested
allocation sizes have to be padded to the next power-of-two size [2].
For example, an allocation of size 96 and alignment of 32 will be padded
to an allocation of size 128, because the existing kmalloc-96 bucket
doesn't guarantee alignent above ARCH_KMALLOC_MINALIGN. Without slab
debugging active, the layout of the kmalloc-96 slabs however naturally
align the objects to 32 bytes, so extending the size to 128 bytes is
wasteful.

To improve the situation we can extend the kmalloc() alignment
guarantees in a way that

1) doesn't change the current slab layout (and thus does not increase
   internal fragmentation) when slab debugging is not active
2) reduces waste in the Rust allocator use case
3) is a superset of the current guarantee for power-of-two sizes.

The extended guarantee is that alignment is at least the largest
power-of-two divisor of the requested size. For power-of-two sizes the
largest divisor is the size itself, but let's keep this case documented
separately for clarity.

For current kmalloc size buckets, it means kmalloc-96 will guarantee
alignment of 32 bytes and kmalloc-196 will guarantee 64 bytes.

This covers the rules 1 and 2 above of Rust's API as long as the size is
a multiple of the alignment. The Rust layer should now only need to
round up the size to the next multiple if it isn't, while enforcing the
rule 3.

Implementation-wise, this changes the alignment calculation in
create_boot_cache(). While at it also do the calulation only for caches
with the SLAB_KMALLOC flag, because the function is also used to create
the initial kmem_cache and kmem_cache_node caches, where no alignment
guarantee is necessary.

In the Rust allocator's krealloc_aligned(), remove the code that padded
sizes to the next power of two (suggested by Alice Ryhl) as it's no
longer necessary with the new guarantees.

Reported-by: Alice Ryhl <aliceryhl@google.com>
Reported-by: Boqun Feng <boqun.feng@gmail.com>
Link: https://lore.kernel.org/all/CAH5fLggjrbdUuT-H-5vbQfMazjRDpp2%2Bk3%3DYhPyS17ezEqxwcw@mail.gmail.com/ [1]
Link: https://lore.kernel.org/all/CAH5fLghsZRemYUwVvhk77o6y1foqnCeDzW4WZv6ScEWna2+_jw@mail.gmail.com/ [2]
Reviewed-by: Boqun Feng <boqun.feng@gmail.com>
Acked-by: Roman Gushchin <roman.gushchin@linux.dev>
Reviewed-by: Alice Ryhl <aliceryhl@google.com>
Signed-off-by: Vlastimil Babka <vbabka@suse.cz>
2024-07-03 12:23:27 +02:00
arch 16 hotfixes, 11 of which are cc:stable. 2024-05-25 15:10:33 -07:00
block block-6.10-20240523 2024-05-23 13:44:47 -07:00
certs kbuild: use $(src) instead of $(srctree)/$(src) for source directory 2024-05-10 04:34:52 +09:00
crypto This push fixes a bug in the new ecc P521 code as well as a buggy 2024-05-20 08:47:54 -07:00
Documentation slab, rust: extend kmalloc() alignment guarantees to remove Rust padding 2024-07-03 12:23:27 +02:00
drivers ipmi: Mostly updates for deprecated interfaces 2024-05-25 14:32:29 -07:00
fs four smb client fixes, including two important netfs integration fixes 2024-05-25 22:33:10 -07:00
include slab, rust: extend kmalloc() alignment guarantees to remove Rust padding 2024-07-03 12:23:27 +02:00
init Driver core changes for 6.10-rc1 2024-05-22 12:13:40 -07:00
io_uring io_uring-6.10-20240523 2024-05-23 13:41:49 -07:00
ipc Mainly singleton patches, documented in their respective changelogs. 2024-05-19 14:02:03 -07:00
kernel Misc fixes: 2024-05-25 14:48:40 -07:00
lib mm, slab: don't wrap internal functions with alloc_hooks() 2024-05-28 09:27:50 +02:00
LICENSES LICENSES: Add the copyleft-next-0.3.1 license 2022-11-08 15:44:01 +01:00
mm slab, rust: extend kmalloc() alignment guarantees to remove Rust padding 2024-07-03 12:23:27 +02:00
net NFS client updates for Linux 6.10 2024-05-23 13:51:09 -07:00
rust slab, rust: extend kmalloc() alignment guarantees to remove Rust padding 2024-07-03 12:23:27 +02:00
samples tracing/treewide: Remove second parameter of __assign_str() 2024-05-22 20:14:47 -04:00
scripts - A series ("kbuild: enable more warnings by default") from Arnd 2024-05-22 18:59:29 -07:00
security hardening fixes for v6.10-rc1 2024-05-24 08:33:44 -07:00
sound sound fixes for 6.10-rc1 2024-05-24 08:48:51 -07:00
tools slab: delete useless RED_INACTIVE and RED_ACTIVE 2024-06-24 21:41:41 +02:00
usr kbuild: use $(src) instead of $(srctree)/$(src) for source directory 2024-05-10 04:34:52 +09:00
virt The usual shower of singleton fixes and minor series all over MM, 2024-05-19 09:21:03 -07:00
.clang-format clang-format: Update with v6.7-rc4's for_each macro list 2023-12-08 23:54:38 +01:00
.cocciconfig
.editorconfig Add .editorconfig file for basic formatting 2023-12-28 16:22:47 +09:00
.get_maintainer.ignore Add Jeff Kirsher to .get_maintainer.ignore 2024-03-08 11:36:54 +00:00
.gitattributes .gitattributes: set diff driver for Rust source code files 2023-05-31 17:48:25 +02:00
.gitignore kbuild: create a list of all built DTB files 2024-02-19 18:20:39 +09:00
.mailmap mailmap: update email address for Satya Priya 2024-05-24 11:55:05 -07:00
.rustfmt.toml rust: add .rustfmt.toml 2022-09-28 09:02:20 +02:00
COPYING COPYING: state that all contributions really are covered by this file 2020-02-10 13:32:20 -08:00
CREDITS MAINTAINERS: Drop Gustavo Pimentel as PCI DWC Maintainer 2024-03-27 13:41:02 -05:00
Kbuild Kbuild updates for v6.1 2022-10-10 12:00:45 -07:00
Kconfig kbuild: ensure full rebuild when the compiler is updated 2020-05-12 13:28:33 +09:00
MAINTAINERS RTC for 6.10 2024-05-25 13:33:53 -07:00
Makefile Linux 6.10-rc1 2024-05-26 15:20:12 -07:00
README README: Fix spelling 2024-03-18 03:36:32 -06:00

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.