git: kmalloc: Use 'fls' to round up the size to the nearest power of 2
Matthew Dillon
dillon at apollo.backplane.com
Mon Oct 8 09:45:47 PDT 2012
:http://gitweb.dragonflybsd.org/dragonfly.git/commitdiff/1e57f8673c953ace8a25ada0a39ab83008646ce3
:
For cache alignment any allocation that is already a power of 2 will be
at least that specific power-of-2 aligned. Any allocation that is not
a power of 2 will be aligned to the slab chunking:
* Alloc Size Chunking Number of zones
* 0-127 8 16
* 128-255 16 8
* 256-511 32 8
* 512-1023 64 8
...
What this means is that in order to cache align an allocation you only
need to do it for allocations < 256 bytes (if the cache line size is
32 bytes). Any allocation >= 256 bytes will be at least 32-byte aligned
even if it is not a power of 2.
So we don't necessarily need to enforce a power-of-2 size in all cases,
only in cases where the allocation size < 256 bytes.
-Matt
Matthew Dillon
<dillon at backplane.com>
More information about the Commits
mailing list