* Features:
- Low metadata overhead (just 4 bytes per object)
- O(1) Alloc/Free - except when we have to call system page allocator to
get additional memory.
- Very low fragmentation: In all tests, xvmalloc memory usage is within 12%
of "Ideal".
- Pool based allocator: Each pool can grow and shrink.
- It maps pages only when required. So, it does not hog vmalloc area which
is very small on 32-bit systems.
SLUB allocator could not be used due to fragmentation issues:
http://code.google.com/p/compcache/wiki/AllocatorsComparison
Data here shows kmalloc using ~43% more memory than TLSF and xvMalloc
is showed ~2% more space efficiency than TLSF (due to smaller metadata).
Creating various kmem_caches can reduce space efficiency gap but still
problem of being limited to low memory exists. Also, it depends on
allocating higher order pages to reduce fragmentation - this is not
acceptable for ramzswap as it is used under memory crunch (its a swap
device!).
SLOB allocator could not be used do to reasons mentioned here:
http://lkml.org/lkml/2009/3/18/210
* Implementation:
It uses two-level bitmap search to find free list containing block of
correct size. This idea is taken from TLSF (Two-Level Segregate Fit)
allocator and is well explained in its paper (see [Links] below).
* Limitations:
- Poor scalability: No per-cpu data structures (work in progress).
[Links]
1. Details and Performance data:
http://code.google.com/p/compcache/wiki/xvMallochttp://code.google.com/p/compcache/wiki/xvMallocPerformance
2. TLSF memory allocator:
home: http://rtportal.upv.es/rtmalloc/
paper: http://rtportal.upv.es/rtmalloc/files/MRBC_2008.pdf
Signed-off-by: Nitin Gupta <ngupta@vflare.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
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