36071a279b
kmalloc_index() return index into an array of kmalloc kmem caches,
therefore should be unsigned.
Space savings with SLUB on trimmed down .config:
add/remove: 0/1 grow/shrink: 6/56 up/down: 85/-557 (-472)
Function old new delta
calculate_sizes 924 983 +59
on_freelist 589 604 +15
init_cache_random_seq 122 127 +5
ext4_mb_init 1206 1210 +4
slab_pad_check.part 270 271 +1
cpu_partial_store 112 113 +1
usersize_show 28 27 -1
...
new_slab 1871 1837 -34
slab_order 204 - -204
This patch start a series of converting SLUB (mostly) to "unsigned int".
1) Most integers in the code are in fact unsigned entities: array
indexes, lengths, buffer sizes, allocation orders. It is therefore
better to use unsigned variables
2) Some integers in the code are either "size_t" or "unsigned long" for
no reason.
size_t usually comes from people trying to maintain type correctness
and figuring out that "sizeof" operator returns size_t or
memset/memcpy takes size_t so should everything passed to it.
However the number of 4GB+ objects in the kernel is very small. Most,
if not all, dynamically allocated objects with kmalloc() or
kmem_cache_create() aren't actually big. Maintaining wide types
doesn't do anything.
64-bit ops are bigger than 32-bit on our beloved x86_64,
so try to not use 64-bit where it isn't necessary
(read: everywhere where integers are integers not pointers)
3) in case of SLAB allocators, there are additional limitations
*) page->inuse, page->objects are only 16-/15-bit,
*) cache size was always 32-bit
*) slab orders are small, order 20 is needed to go 64-bit on x86_64
(PAGE_SIZE << order)
Basically everything is 32-bit except kmalloc(1ULL<<32) which gets
shortcut through page allocator.
Christoph said:
:
: That changes with large base page size on power and ARM64 f.e. but then
: we do not want to encourage larger allocations through slab anyways.
Link: http://lkml.kernel.org/r/20180305200730.15812-2-adobriyan@gmail.com
Signed-off-by: Alexey Dobriyan <adobriyan@gmail.com>
Acked-by: Christoph Lameter <cl@linux.com>
Cc: Pekka Enberg <penberg@kernel.org>
Cc: David Rientjes <rientjes@google.com>
Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
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 Restructured Text markup notation.
See Documentation/00-INDEX for a list of what is contained in each file.
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.