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Subject[PATCH 3/3] ramzswap documentation
  Documentation/blockdev/00-INDEX     |    2 +
Documentation/blockdev/ramzswap.txt | 67 +++++++++++++++++++++++++++++++++++
Documentation/kernel-parameters.txt | 9 +++++
3 files changed, 78 insertions(+), 0 deletions(-)

Documentation on how to use ramzswap module.

Signed-off-by: Nitin Gupta <>

diff --git a/Documentation/blockdev/00-INDEX b/Documentation/blockdev/00-INDEX
index 86f054c..8751488 100644
--- a/Documentation/blockdev/00-INDEX
+++ b/Documentation/blockdev/00-INDEX
@@ -4,6 +4,8 @@ README.DAC960
- info on Mylex DAC960/DAC1100 PCI RAID Controller Driver for Linux.
- info, major/minor #'s for Compaq's SMART Array Controllers.
+ - short guide on how to setup compressed RAM swap device.
- info on using Compaq's SMART2 Intelligent Disk Array Controllers.
diff --git a/Documentation/blockdev/ramzswap.txt b/Documentation/blockdev/ramzswap.txt
new file mode 100644
index 0000000..835afcf
--- /dev/null
+++ b/Documentation/blockdev/ramzswap.txt
@@ -0,0 +1,67 @@
+ramzswap: Compressed RAM swap device
+Project home:
+This module creates RAM based block device (named ramzswap0) which acts
+as swap disk. Pages swapped to this disk are compressed and stored in
+memory itself.
+It uses these components:
+ - xvMalloc: memory allocator (xvmalloc.ko)
+ - LZO1X: de/compressor: (lzo_compress.ko, lzo_decompress.ko)
+ - modprobe ramzswap [memlimit_kb=<val>|disksize_kb=<val>] [backing_swap=<dev>]
+ memlimit_kb: This param is applicable only when backing_swap is given.
+ It is limit on amount compressed data stored in memory. Any
+ additional data is forwarded to backing_swap. It cannot be greater
+ than backing device size. If missing or 0, default value is used:
+ 15% of RAM or backing device size, whichever is smaller.
+ disksize_kb: This param is applicable only when backing_swap is not given.
+ It is limit on amount of *uncompressed* worth of data stored in
+ memory. For e.g. disksize_kb=1024 means it can hold 1024kb worth of
+ uncompressed data even if this data compresses to just, say, 100kb.
+ If missing or 0, default value is used: 25% of RAM.
+ backing_swap: This is block device to be used as backing store for ramzswap.
+ It must be a valid swap partition. We move data to this device when we
+ encounter incompressible page or memlimit is reached. TODO: we may also
+ move some pages from ramzswap to this device in case system is really
+ low on memory.
+ This device is not directly visible to kernel as a swap device
+ (/proc/swaps will only show /dev/ramzswap0 and not this device).
+ Managing this backing device is the job of ramzswap module.
+ 1) modprobe ramzswap memlimit_kb=10240 backing_swap=/dev/sda2
+ sets ramzswap limit as 10MB and /dev/sda2 as backing swap device.
+ NOTE: here /dev/sda2 is a valid swap partition.
+ 2) modprobe ramzswap backing_swap=/dev/sda2
+ same as (1) but memlimit is set to default: 15% of RAM or size of
+ backing swap device, whichever is smaller.
+ 3) modprobe ramzswap disksize_kb=10240
+ sets ramzswap disk size as 10MB.
+ 4) modprobe ramzswap.ko
+ same as (3) but ramzswap disk size will be set to default:
+ 25% of RAM size.
+ Once module is loaded, activate this swap with highest priority:
+ swapon /dev/ramzswap0 -p 100
+ (-p param set swap priority)
+ - ramzswap stats are exported via /proc/ramzswap
+ - If you give non-swap partition as backing_swap, nothing bad will happen -
+ swapon will simply fail to recognize /dev/ramzswap0 as swap partition.
+ So, in this case, unload the module and reload with correct backing_swap.
+Please report any problems to:
+Nitin Gupta
diff --git a/Documentation/kernel-parameters.txt b/Documentation/kernel-parameters.txt
index be3bde5..1cb1d2e 100644
--- a/Documentation/kernel-parameters.txt
+++ b/Documentation/kernel-parameters.txt
@@ -415,6 +415,15 @@ and is between 256 and 4096 characters. It is defined in the file
possible to determine what the correct size should be.
This option provides an override for these situations.

+ ramzswap.memlimit_kb=
+ See Documentation/blockdev/ramzswap.txt.
+ ramzswap.disksize_kb=
+ See Documentation/blockdev/ramzswap.txt.
+ ramzswap.backing_swap=
+ See Documentation/blockdev/ramzswap.txt.
security= [SECURITY] Choose a security module to enable at boot.
If this boot parameter is not specified, only the first
security module asking for security registration will be

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