Commit graph

5 commits

Author SHA1 Message Date
Nitin Gupta
30fb8a7141 Staging: ramzswap: remove ARM specific d-cache hack
Remove d-cache hack in ramzswap driver that was needed
to workaround a bug in ARM version of update_mmu_cache()
which caused stale data in d-cache to be transferred to
userspace. This bug was fixed by git commit:
	787b2faadc
This also brings down one entry in TODO file.

Signed-off-by: Nitin Gupta <ngupta@vflare.org>
Acked-by: Pekka Enberg <penberg@cs.helsinki.fi>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
2009-12-23 11:27:49 -08:00
Nitin Gupta
224f0ef4e2 Staging: ramzswap: add TODO file
TODO file for ramzswap.

Signed-off-by: Nitin Gupta <ngupta@vflare.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
2009-12-11 12:23:04 -08:00
Nitin Gupta
47f9afb38f Staging: ramzswap: documentation
Short guide on how to setup and use ramzswap.

Signed-off-by: Nitin Gupta <ngupta@vflare.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
2009-12-11 12:23:04 -08:00
Nitin Gupta
306b0c957f Staging: virtual block device driver (ramzswap)
Creates RAM based block devices (/dev/ramzswapX) which can be
used (only) as swap disks. Pages swapped to these are compressed
and stored in memory itself.

The module is called ramzswap.ko. It depends on:
 - xvmalloc memory allocator (compiled with this driver)
 - lzo_compress.ko
 - lzo_decompress.ko

See ramzswap.txt for usage details.

Signed-off-by: Nitin Gupta <ngupta@vflare.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
2009-12-11 12:23:04 -08:00
Nitin Gupta
644bf7b598 Staging: xvmalloc memory allocator
* 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/xvMalloc
http://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>
2009-12-11 12:23:04 -08:00