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docs: blockdev: add it to the admin-guide

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The blockdev book basically contains user-faced documentation.

Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org>
This commit is contained in:
Mauro Carvalho Chehab
2019-06-18 11:47:10 -03:00
parent 330d481052
commit e7751617dd
22 changed files with 24 additions and 26 deletions
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digraph conn_states {
StandAllone -> WFConnection [ label = "ioctl_set_net()" ]
WFConnection -> Unconnected [ label = "unable to bind()" ]
WFConnection -> WFReportParams [ label = "in connect() after accept" ]
WFReportParams -> StandAllone [ label = "checks in receive_param()" ]
WFReportParams -> Connected [ label = "in receive_param()" ]
WFReportParams -> WFBitMapS [ label = "sync_handshake()" ]
WFReportParams -> WFBitMapT [ label = "sync_handshake()" ]
WFBitMapS -> SyncSource [ label = "receive_bitmap()" ]
WFBitMapT -> SyncTarget [ label = "receive_bitmap()" ]
SyncSource -> Connected
SyncTarget -> Connected
SyncSource -> PausedSyncS
SyncTarget -> PausedSyncT
PausedSyncS -> SyncSource
PausedSyncT -> SyncTarget
Connected -> WFConnection [ label = "* on network error" ]
}

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================================
kernel data structure for DRBD-9
================================
This describes the in kernel data structure for DRBD-9. Starting with
Linux v3.14 we are reorganizing DRBD to use this data structure.
Basic Data Structure
====================
A node has a number of DRBD resources. Each such resource has a number of
devices (aka volumes) and connections to other nodes ("peer nodes"). Each DRBD
device is represented by a block device locally.
The DRBD objects are interconnected to form a matrix as depicted below; a
drbd_peer_device object sits at each intersection between a drbd_device and a
drbd_connection::
/--------------+---------------+.....+---------------\
| resource | device | | device |
+--------------+---------------+.....+---------------+
| connection | peer_device | | peer_device |
+--------------+---------------+.....+---------------+
: : : : :
: : : : :
+--------------+---------------+.....+---------------+
| connection | peer_device | | peer_device |
\--------------+---------------+.....+---------------/
In this table, horizontally, devices can be accessed from resources by their
volume number. Likewise, peer_devices can be accessed from connections by
their volume number. Objects in the vertical direction are connected by double
linked lists. There are back pointers from peer_devices to their connections a
devices, and from connections and devices to their resource.
All resources are in the drbd_resources double-linked list. In addition, all
devices can be accessed by their minor device number via the drbd_devices idr.
The drbd_resource, drbd_connection, and drbd_device objects are reference
counted. The peer_device objects only serve to establish the links between
devices and connections; their lifetime is determined by the lifetime of the
device and connection which they reference.

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digraph disk_states {
Diskless -> Inconsistent [ label = "ioctl_set_disk()" ]
Diskless -> Consistent [ label = "ioctl_set_disk()" ]
Diskless -> Outdated [ label = "ioctl_set_disk()" ]
Consistent -> Outdated [ label = "receive_param()" ]
Consistent -> UpToDate [ label = "receive_param()" ]
Consistent -> Inconsistent [ label = "start resync" ]
Outdated -> Inconsistent [ label = "start resync" ]
UpToDate -> Inconsistent [ label = "ioctl_replicate" ]
Inconsistent -> UpToDate [ label = "resync completed" ]
Consistent -> Failed [ label = "io completion error" ]
Outdated -> Failed [ label = "io completion error" ]
UpToDate -> Failed [ label = "io completion error" ]
Inconsistent -> Failed [ label = "io completion error" ]
Failed -> Diskless [ label = "sending notify to peer" ]
}

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// vim: set sw=2 sts=2 :
digraph {
rankdir=BT
bgcolor=white
node [shape=plaintext]
node [fontcolor=black]
StandAlone [ style=filled,fillcolor=gray,label=StandAlone ]
node [fontcolor=lightgray]
Unconnected [ label=Unconnected ]
CommTrouble [ shape=record,
label="{communication loss|{Timeout|BrokenPipe|NetworkFailure}}" ]
node [fontcolor=gray]
subgraph cluster_try_connect {
label="try to connect, handshake"
rank=max
WFConnection [ label=WFConnection ]
WFReportParams [ label=WFReportParams ]
}
TearDown [ label=TearDown ]
Connected [ label=Connected,style=filled,fillcolor=green,fontcolor=black ]
node [fontcolor=lightblue]
StartingSyncS [ label=StartingSyncS ]
StartingSyncT [ label=StartingSyncT ]
subgraph cluster_bitmap_exchange {
node [fontcolor=red]
fontcolor=red
label="new application (WRITE?) requests blocked\lwhile bitmap is exchanged"
WFBitMapT [ label=WFBitMapT ]
WFSyncUUID [ label=WFSyncUUID ]
WFBitMapS [ label=WFBitMapS ]
}
node [fontcolor=blue]
cluster_resync [ shape=record,label="{<any>resynchronisation process running\l'concurrent' application requests allowed|{{<T>PausedSyncT\nSyncTarget}|{<S>PausedSyncS\nSyncSource}}}" ]
node [shape=box,fontcolor=black]
// drbdadm [label="drbdadm connect"]
// handshake [label="drbd_connect()\ndrbd_do_handshake\ndrbd_sync_handshake() etc."]
// comm_error [label="communication trouble"]
//
// edges
// --------------------------------------
StandAlone -> Unconnected [ label="drbdadm connect" ]
Unconnected -> StandAlone [ label="drbdadm disconnect\lor serious communication trouble" ]
Unconnected -> WFConnection [ label="receiver thread is started" ]
WFConnection -> WFReportParams [ headlabel="accept()\land/or \lconnect()\l" ]
WFReportParams -> StandAlone [ label="during handshake\lpeers do not agree\labout something essential" ]
WFReportParams -> Connected [ label="data identical\lno sync needed",color=green,fontcolor=green ]
WFReportParams -> WFBitMapS
WFReportParams -> WFBitMapT
WFBitMapT -> WFSyncUUID [minlen=0.1,constraint=false]
WFBitMapS -> cluster_resync:S
WFSyncUUID -> cluster_resync:T
edge [color=green]
cluster_resync:any -> Connected [ label="resnyc done",fontcolor=green ]
edge [color=red]
WFReportParams -> CommTrouble
Connected -> CommTrouble
cluster_resync:any -> CommTrouble
edge [color=black]
CommTrouble -> Unconnected [label="receiver thread is stopped" ]
}

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.. The here included files are intended to help understand the implementation
Data flows that Relate some functions, and write packets
========================================================
.. kernel-figure:: DRBD-8.3-data-packets.svg
:alt: DRBD-8.3-data-packets.svg
:align: center
.. kernel-figure:: DRBD-data-packets.svg
:alt: DRBD-data-packets.svg
:align: center
Sub graphs of DRBD's state transitions
======================================
.. kernel-figure:: conn-states-8.dot
:alt: conn-states-8.dot
:align: center
.. kernel-figure:: disk-states-8.dot
:alt: disk-states-8.dot
:align: center
.. kernel-figure:: node-states-8.dot
:alt: node-states-8.dot
:align: center

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==========================================
Distributed Replicated Block Device - DRBD
==========================================
Description
===========
DRBD is a shared-nothing, synchronously replicated block device. It
is designed to serve as a building block for high availability
clusters and in this context, is a "drop-in" replacement for shared
storage. Simplistically, you could see it as a network RAID 1.
Please visit http://www.drbd.org to find out more.
.. toctree::
:maxdepth: 1
data-structure-v9
figures

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digraph node_states {
Secondary -> Primary [ label = "ioctl_set_state()" ]
Primary -> Secondary [ label = "ioctl_set_state()" ]
}
digraph peer_states {
Secondary -> Primary [ label = "recv state packet" ]
Primary -> Secondary [ label = "recv state packet" ]
Primary -> Unknown [ label = "connection lost" ]
Secondary -> Unknown [ label = "connection lost" ]
Unknown -> Primary [ label = "connected" ]
Unknown -> Secondary [ label = "connected" ]
}

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=============
Floppy Driver
=============
FAQ list:
=========
A FAQ list may be found in the fdutils package (see below), and also
at <http://fdutils.linux.lu/faq.html>.
LILO configuration options (Thinkpad users, read this)
======================================================
The floppy driver is configured using the 'floppy=' option in
lilo. This option can be typed at the boot prompt, or entered in the
lilo configuration file.
Example: If your kernel is called linux-2.6.9, type the following line
at the lilo boot prompt (if you have a thinkpad)::
linux-2.6.9 floppy=thinkpad
You may also enter the following line in /etc/lilo.conf, in the description
of linux-2.6.9::
append = "floppy=thinkpad"
Several floppy related options may be given, example::
linux-2.6.9 floppy=daring floppy=two_fdc
append = "floppy=daring floppy=two_fdc"
If you give options both in the lilo config file and on the boot
prompt, the option strings of both places are concatenated, the boot
prompt options coming last. That's why there are also options to
restore the default behavior.
Module configuration options
============================
If you use the floppy driver as a module, use the following syntax::
modprobe floppy floppy="<options>"
Example::
modprobe floppy floppy="omnibook messages"
If you need certain options enabled every time you load the floppy driver,
you can put::
options floppy floppy="omnibook messages"
in a configuration file in /etc/modprobe.d/.
The floppy driver related options are:
floppy=asus_pci
Sets the bit mask to allow only units 0 and 1. (default)
floppy=daring
Tells the floppy driver that you have a well behaved floppy controller.
This allows more efficient and smoother operation, but may fail on
certain controllers. This may speed up certain operations.
floppy=0,daring
Tells the floppy driver that your floppy controller should be used
with caution.
floppy=one_fdc
Tells the floppy driver that you have only one floppy controller.
(default)
floppy=two_fdc / floppy=<address>,two_fdc
Tells the floppy driver that you have two floppy controllers.
The second floppy controller is assumed to be at <address>.
This option is not needed if the second controller is at address
0x370, and if you use the 'cmos' option.
floppy=thinkpad
Tells the floppy driver that you have a Thinkpad. Thinkpads use an
inverted convention for the disk change line.
floppy=0,thinkpad
Tells the floppy driver that you don't have a Thinkpad.
floppy=omnibook / floppy=nodma
Tells the floppy driver not to use Dma for data transfers.
This is needed on HP Omnibooks, which don't have a workable
DMA channel for the floppy driver. This option is also useful
if you frequently get "Unable to allocate DMA memory" messages.
Indeed, dma memory needs to be continuous in physical memory,
and is thus harder to find, whereas non-dma buffers may be
allocated in virtual memory. However, I advise against this if
you have an FDC without a FIFO (8272A or 82072). 82072A and
later are OK. You also need at least a 486 to use nodma.
If you use nodma mode, I suggest you also set the FIFO
threshold to 10 or lower, in order to limit the number of data
transfer interrupts.
If you have a FIFO-able FDC, the floppy driver automatically
falls back on non DMA mode if no DMA-able memory can be found.
If you want to avoid this, explicitly ask for 'yesdma'.
floppy=yesdma
Tells the floppy driver that a workable DMA channel is available.
(default)
floppy=nofifo
Disables the FIFO entirely. This is needed if you get "Bus
master arbitration error" messages from your Ethernet card (or
from other devices) while accessing the floppy.
floppy=usefifo
Enables the FIFO. (default)
floppy=<threshold>,fifo_depth
Sets the FIFO threshold. This is mostly relevant in DMA
mode. If this is higher, the floppy driver tolerates more
interrupt latency, but it triggers more interrupts (i.e. it
imposes more load on the rest of the system). If this is
lower, the interrupt latency should be lower too (faster
processor). The benefit of a lower threshold is less
interrupts.
To tune the fifo threshold, switch on over/underrun messages
using 'floppycontrol --messages'. Then access a floppy
disk. If you get a huge amount of "Over/Underrun - retrying"
messages, then the fifo threshold is too low. Try with a
higher value, until you only get an occasional Over/Underrun.
It is a good idea to compile the floppy driver as a module
when doing this tuning. Indeed, it allows to try different
fifo values without rebooting the machine for each test. Note
that you need to do 'floppycontrol --messages' every time you
re-insert the module.
Usually, tuning the fifo threshold should not be needed, as
the default (0xa) is reasonable.
floppy=<drive>,<type>,cmos
Sets the CMOS type of <drive> to <type>. This is mandatory if
you have more than two floppy drives (only two can be
described in the physical CMOS), or if your BIOS uses
non-standard CMOS types. The CMOS types are:
== ==================================
0 Use the value of the physical CMOS
1 5 1/4 DD
2 5 1/4 HD
3 3 1/2 DD
4 3 1/2 HD
5 3 1/2 ED
6 3 1/2 ED
16 unknown or not installed
== ==================================
(Note: there are two valid types for ED drives. This is because 5 was
initially chosen to represent floppy *tapes*, and 6 for ED drives.
AMI ignored this, and used 5 for ED drives. That's why the floppy
driver handles both.)
floppy=unexpected_interrupts
Print a warning message when an unexpected interrupt is received.
(default)
floppy=no_unexpected_interrupts / floppy=L40SX
Don't print a message when an unexpected interrupt is received. This
is needed on IBM L40SX laptops in certain video modes. (There seems
to be an interaction between video and floppy. The unexpected
interrupts affect only performance, and can be safely ignored.)
floppy=broken_dcl
Don't use the disk change line, but assume that the disk was
changed whenever the device node is reopened. Needed on some
boxes where the disk change line is broken or unsupported.
This should be regarded as a stopgap measure, indeed it makes
floppy operation less efficient due to unneeded cache
flushings, and slightly more unreliable. Please verify your
cable, connection and jumper settings if you have any DCL
problems. However, some older drives, and also some laptops
are known not to have a DCL.
floppy=debug
Print debugging messages.
floppy=messages
Print informational messages for some operations (disk change
notifications, warnings about over and underruns, and about
autodetection).
floppy=silent_dcl_clear
Uses a less noisy way to clear the disk change line (which
doesn't involve seeks). Implied by 'daring' option.
floppy=<nr>,irq
Sets the floppy IRQ to <nr> instead of 6.
floppy=<nr>,dma
Sets the floppy DMA channel to <nr> instead of 2.
floppy=slow
Use PS/2 stepping rate::
PS/2 floppies have much slower step rates than regular floppies.
It's been recommended that take about 1/4 of the default speed
in some more extreme cases.
Supporting utilities and additional documentation:
==================================================
Additional parameters of the floppy driver can be configured at
runtime. Utilities which do this can be found in the fdutils package.
This package also contains a new version of mtools which allows to
access high capacity disks (up to 1992K on a high density 3 1/2 disk!).
It also contains additional documentation about the floppy driver.
The latest version can be found at fdutils homepage:
http://fdutils.linux.lu
The fdutils releases can be found at:
http://fdutils.linux.lu/download.html
http://www.tux.org/pub/knaff/fdutils/
ftp://metalab.unc.edu/pub/Linux/utils/disk-management/
Reporting problems about the floppy driver
==========================================
If you have a question or a bug report about the floppy driver, mail
me at Alain.Knaff@poboxes.com . If you post to Usenet, preferably use
comp.os.linux.hardware. As the volume in these groups is rather high,
be sure to include the word "floppy" (or "FLOPPY") in the subject
line. If the reported problem happens when mounting floppy disks, be
sure to mention also the type of the filesystem in the subject line.
Be sure to read the FAQ before mailing/posting any bug reports!
Alain
Changelog
=========
10-30-2004 :
Cleanup, updating, add reference to module configuration.
James Nelson <james4765@gmail.com>
6-3-2000 :
Original Document

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===========================
The Linux RapidIO Subsystem
===========================
.. toctree::
:maxdepth: 1
floppy
nbd
paride
ramdisk
zram
drbd/index

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==================================
Network Block Device (TCP version)
==================================
1) Overview
-----------
What is it: With this compiled in the kernel (or as a module), Linux
can use a remote server as one of its block devices. So every time
the client computer wants to read, e.g., /dev/nb0, it sends a
request over TCP to the server, which will reply with the data read.
This can be used for stations with low disk space (or even diskless)
to borrow disk space from another computer.
Unlike NFS, it is possible to put any filesystem on it, etc.
For more information, or to download the nbd-client and nbd-server
tools, go to http://nbd.sf.net/.
The nbd kernel module need only be installed on the client
system, as the nbd-server is completely in userspace. In fact,
the nbd-server has been successfully ported to other operating
systems, including Windows.
A) NBD parameters
-----------------
max_part
Number of partitions per device (default: 0).
nbds_max
Number of block devices that should be initialized (default: 16).

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===================================
Linux and parallel port IDE devices
===================================
PARIDE v1.03 (c) 1997-8 Grant Guenther <grant@torque.net>
1. Introduction
===============
Owing to the simplicity and near universality of the parallel port interface
to personal computers, many external devices such as portable hard-disk,
CD-ROM, LS-120 and tape drives use the parallel port to connect to their
host computer. While some devices (notably scanners) use ad-hoc methods
to pass commands and data through the parallel port interface, most
external devices are actually identical to an internal model, but with
a parallel-port adapter chip added in. Some of the original parallel port
adapters were little more than mechanisms for multiplexing a SCSI bus.
(The Iomega PPA-3 adapter used in the ZIP drives is an example of this
approach). Most current designs, however, take a different approach.
The adapter chip reproduces a small ISA or IDE bus in the external device
and the communication protocol provides operations for reading and writing
device registers, as well as data block transfer functions. Sometimes,
the device being addressed via the parallel cable is a standard SCSI
controller like an NCR 5380. The "ditto" family of external tape
drives use the ISA replicator to interface a floppy disk controller,
which is then connected to a floppy-tape mechanism. The vast majority
of external parallel port devices, however, are now based on standard
IDE type devices, which require no intermediate controller. If one
were to open up a parallel port CD-ROM drive, for instance, one would
find a standard ATAPI CD-ROM drive, a power supply, and a single adapter
that interconnected a standard PC parallel port cable and a standard
IDE cable. It is usually possible to exchange the CD-ROM device with
any other device using the IDE interface.
The document describes the support in Linux for parallel port IDE
devices. It does not cover parallel port SCSI devices, "ditto" tape
drives or scanners. Many different devices are supported by the
parallel port IDE subsystem, including:
- MicroSolutions backpack CD-ROM
- MicroSolutions backpack PD/CD
- MicroSolutions backpack hard-drives
- MicroSolutions backpack 8000t tape drive
- SyQuest EZ-135, EZ-230 & SparQ drives
- Avatar Shark
- Imation Superdisk LS-120
- Maxell Superdisk LS-120
- FreeCom Power CD
- Hewlett-Packard 5GB and 8GB tape drives
- Hewlett-Packard 7100 and 7200 CD-RW drives
as well as most of the clone and no-name products on the market.
To support such a wide range of devices, PARIDE, the parallel port IDE
subsystem, is actually structured in three parts. There is a base
paride module which provides a registry and some common methods for
accessing the parallel ports. The second component is a set of
high-level drivers for each of the different types of supported devices:
=== =============
pd IDE disk
pcd ATAPI CD-ROM
pf ATAPI disk
pt ATAPI tape
pg ATAPI generic
=== =============
(Currently, the pg driver is only used with CD-R drives).
The high-level drivers function according to the relevant standards.
The third component of PARIDE is a set of low-level protocol drivers
for each of the parallel port IDE adapter chips. Thanks to the interest
and encouragement of Linux users from many parts of the world,
support is available for almost all known adapter protocols:
==== ====================================== ====
aten ATEN EH-100 (HK)
bpck Microsolutions backpack (US)
comm DataStor (old-type) "commuter" adapter (TW)
dstr DataStor EP-2000 (TW)
epat Shuttle EPAT (UK)
epia Shuttle EPIA (UK)
fit2 FIT TD-2000 (US)
fit3 FIT TD-3000 (US)
friq Freecom IQ cable (DE)
frpw Freecom Power (DE)
kbic KingByte KBIC-951A and KBIC-971A (TW)
ktti KT Technology PHd adapter (SG)
on20 OnSpec 90c20 (US)
on26 OnSpec 90c26 (US)
==== ====================================== ====
2. Using the PARIDE subsystem
=============================
While configuring the Linux kernel, you may choose either to build
the PARIDE drivers into your kernel, or to build them as modules.
In either case, you will need to select "Parallel port IDE device support"
as well as at least one of the high-level drivers and at least one
of the parallel port communication protocols. If you do not know
what kind of parallel port adapter is used in your drive, you could
begin by checking the file names and any text files on your DOS
installation floppy. Alternatively, you can look at the markings on
the adapter chip itself. That's usually sufficient to identify the
correct device.
You can actually select all the protocol modules, and allow the PARIDE
subsystem to try them all for you.
For the "brand-name" products listed above, here are the protocol
and high-level drivers that you would use:
================ ============ ====== ========
Manufacturer Model Driver Protocol
================ ============ ====== ========
MicroSolutions CD-ROM pcd bpck
MicroSolutions PD drive pf bpck
MicroSolutions hard-drive pd bpck
MicroSolutions 8000t tape pt bpck
SyQuest EZ, SparQ pd epat
Imation Superdisk pf epat
Maxell Superdisk pf friq
Avatar Shark pd epat
FreeCom CD-ROM pcd frpw
Hewlett-Packard 5GB Tape pt epat
Hewlett-Packard 7200e (CD) pcd epat
Hewlett-Packard 7200e (CD-R) pg epat
================ ============ ====== ========
2.1 Configuring built-in drivers
---------------------------------
We recommend that you get to know how the drivers work and how to
configure them as loadable modules, before attempting to compile a
kernel with the drivers built-in.
If you built all of your PARIDE support directly into your kernel,
and you have just a single parallel port IDE device, your kernel should
locate it automatically for you. If you have more than one device,
you may need to give some command line options to your bootloader
(eg: LILO), how to do that is beyond the scope of this document.
The high-level drivers accept a number of command line parameters, all
of which are documented in the source files in linux/drivers/block/paride.
By default, each driver will automatically try all parallel ports it
can find, and all protocol types that have been installed, until it finds
a parallel port IDE adapter. Once it finds one, the probe stops. So,
if you have more than one device, you will need to tell the drivers
how to identify them. This requires specifying the port address, the
protocol identification number and, for some devices, the drive's
chain ID. While your system is booting, a number of messages are
displayed on the console. Like all such messages, they can be
reviewed with the 'dmesg' command. Among those messages will be
some lines like::
paride: bpck registered as protocol 0
paride: epat registered as protocol 1
The numbers will always be the same until you build a new kernel with
different protocol selections. You should note these numbers as you
will need them to identify the devices.
If you happen to be using a MicroSolutions backpack device, you will
also need to know the unit ID number for each drive. This is usually
the last two digits of the drive's serial number (but read MicroSolutions'
documentation about this).
As an example, let's assume that you have a MicroSolutions PD/CD drive
with unit ID number 36 connected to the parallel port at 0x378, a SyQuest
EZ-135 connected to the chained port on the PD/CD drive and also an
Imation Superdisk connected to port 0x278. You could give the following
options on your boot command::
pd.drive0=0x378,1 pf.drive0=0x278,1 pf.drive1=0x378,0,36
In the last option, pf.drive1 configures device /dev/pf1, the 0x378
is the parallel port base address, the 0 is the protocol registration
number and 36 is the chain ID.
Please note: while PARIDE will work both with and without the
PARPORT parallel port sharing system that is included by the
"Parallel port support" option, PARPORT must be included and enabled
if you want to use chains of devices on the same parallel port.
2.2 Loading and configuring PARIDE as modules
----------------------------------------------
It is much faster and simpler to get to understand the PARIDE drivers
if you use them as loadable kernel modules.
Note 1:
using these drivers with the "kerneld" automatic module loading
system is not recommended for beginners, and is not documented here.
Note 2:
if you build PARPORT support as a loadable module, PARIDE must
also be built as loadable modules, and PARPORT must be loaded before
the PARIDE modules.
To use PARIDE, you must begin by::
insmod paride
this loads a base module which provides a registry for the protocols,
among other tasks.
Then, load as many of the protocol modules as you think you might need.
As you load each module, it will register the protocols that it supports,
and print a log message to your kernel log file and your console. For
example::
# insmod epat
paride: epat registered as protocol 0
# insmod kbic
paride: k951 registered as protocol 1
paride: k971 registered as protocol 2
Finally, you can load high-level drivers for each kind of device that
you have connected. By default, each driver will autoprobe for a single
device, but you can support up to four similar devices by giving their
individual co-ordinates when you load the driver.
For example, if you had two no-name CD-ROM drives both using the
KingByte KBIC-951A adapter, one on port 0x378 and the other on 0x3bc
you could give the following command::
# insmod pcd drive0=0x378,1 drive1=0x3bc,1
For most adapters, giving a port address and protocol number is sufficient,
but check the source files in linux/drivers/block/paride for more
information. (Hopefully someone will write some man pages one day !).
As another example, here's what happens when PARPORT is installed, and
a SyQuest EZ-135 is attached to port 0x378::
# insmod paride
paride: version 1.0 installed
# insmod epat
paride: epat registered as protocol 0
# insmod pd
pd: pd version 1.0, major 45, cluster 64, nice 0
pda: Sharing parport1 at 0x378
pda: epat 1.0, Shuttle EPAT chip c3 at 0x378, mode 5 (EPP-32), delay 1
pda: SyQuest EZ135A, 262144 blocks [128M], (512/16/32), removable media
pda: pda1
Note that the last line is the output from the generic partition table
scanner - in this case it reports that it has found a disk with one partition.
2.3 Using a PARIDE device
--------------------------
Once the drivers have been loaded, you can access PARIDE devices in the
same way as their traditional counterparts. You will probably need to
create the device "special files". Here is a simple script that you can
cut to a file and execute::
#!/bin/bash
#
# mkd -- a script to create the device special files for the PARIDE subsystem
#
function mkdev {
mknod $1 $2 $3 $4 ; chmod 0660 $1 ; chown root:disk $1
}
#
function pd {
D=$( printf \\$( printf "x%03x" $[ $1 + 97 ] ) )
mkdev pd$D b 45 $[ $1 * 16 ]
for P in 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15
do mkdev pd$D$P b 45 $[ $1 * 16 + $P ]
done
}
#
cd /dev
#
for u in 0 1 2 3 ; do pd $u ; done
for u in 0 1 2 3 ; do mkdev pcd$u b 46 $u ; done
for u in 0 1 2 3 ; do mkdev pf$u b 47 $u ; done
for u in 0 1 2 3 ; do mkdev pt$u c 96 $u ; done
for u in 0 1 2 3 ; do mkdev npt$u c 96 $[ $u + 128 ] ; done
for u in 0 1 2 3 ; do mkdev pg$u c 97 $u ; done
#
# end of mkd
With the device files and drivers in place, you can access PARIDE devices
like any other Linux device. For example, to mount a CD-ROM in pcd0, use::
mount /dev/pcd0 /cdrom
If you have a fresh Avatar Shark cartridge, and the drive is pda, you
might do something like::
fdisk /dev/pda -- make a new partition table with
partition 1 of type 83
mke2fs /dev/pda1 -- to build the file system
mkdir /shark -- make a place to mount the disk
mount /dev/pda1 /shark
Devices like the Imation superdisk work in the same way, except that
they do not have a partition table. For example to make a 120MB
floppy that you could share with a DOS system::
mkdosfs /dev/pf0
mount /dev/pf0 /mnt
2.4 The pf driver
------------------
The pf driver is intended for use with parallel port ATAPI disk
devices. The most common devices in this category are PD drives
and LS-120 drives. Traditionally, media for these devices are not
partitioned. Consequently, the pf driver does not support partitioned
media. This may be changed in a future version of the driver.
2.5 Using the pt driver
------------------------
The pt driver for parallel port ATAPI tape drives is a minimal driver.
It does not yet support many of the standard tape ioctl operations.
For best performance, a block size of 32KB should be used. You will
probably want to set the parallel port delay to 0, if you can.
2.6 Using the pg driver
------------------------
The pg driver can be used in conjunction with the cdrecord program
to create CD-ROMs. Please get cdrecord version 1.6.1 or later
from ftp://ftp.fokus.gmd.de/pub/unix/cdrecord/ . To record CD-R media
your parallel port should ideally be set to EPP mode, and the "port delay"
should be set to 0. With those settings it is possible to record at 2x
speed without any buffer underruns. If you cannot get the driver to work
in EPP mode, try to use "bidirectional" or "PS/2" mode and 1x speeds only.
3. Troubleshooting
==================
3.1 Use EPP mode if you can
----------------------------
The most common problems that people report with the PARIDE drivers
concern the parallel port CMOS settings. At this time, none of the
PARIDE protocol modules support ECP mode, or any ECP combination modes.
If you are able to do so, please set your parallel port into EPP mode
using your CMOS setup procedure.
3.2 Check the port delay
-------------------------
Some parallel ports cannot reliably transfer data at full speed. To
offset the errors, the PARIDE protocol modules introduce a "port
delay" between each access to the i/o ports. Each protocol sets
a default value for this delay. In most cases, the user can override
the default and set it to 0 - resulting in somewhat higher transfer
rates. In some rare cases (especially with older 486 systems) the
default delays are not long enough. if you experience corrupt data
transfers, or unexpected failures, you may wish to increase the
port delay. The delay can be programmed using the "driveN" parameters
to each of the high-level drivers. Please see the notes above, or
read the comments at the beginning of the driver source files in
linux/drivers/block/paride.
3.3 Some drives need a printer reset
-------------------------------------
There appear to be a number of "noname" external drives on the market
that do not always power up correctly. We have noticed this with some
drives based on OnSpec and older Freecom adapters. In these rare cases,
the adapter can often be reinitialised by issuing a "printer reset" on
the parallel port. As the reset operation is potentially disruptive in
multiple device environments, the PARIDE drivers will not do it
automatically. You can however, force a printer reset by doing::
insmod lp reset=1
rmmod lp
If you have one of these marginal cases, you should probably build
your paride drivers as modules, and arrange to do the printer reset
before loading the PARIDE drivers.
3.4 Use the verbose option and dmesg if you need help
------------------------------------------------------
While a lot of testing has gone into these drivers to make them work
as smoothly as possible, problems will arise. If you do have problems,
please check all the obvious things first: does the drive work in
DOS with the manufacturer's drivers ? If that doesn't yield any useful
clues, then please make sure that only one drive is hooked to your system,
and that either (a) PARPORT is enabled or (b) no other device driver
is using your parallel port (check in /proc/ioports). Then, load the
appropriate drivers (you can load several protocol modules if you want)
as in::
# insmod paride
# insmod epat
# insmod bpck
# insmod kbic
...
# insmod pd verbose=1
(using the correct driver for the type of device you have, of course).
The verbose=1 parameter will cause the drivers to log a trace of their
activity as they attempt to locate your drive.
Use 'dmesg' to capture a log of all the PARIDE messages (any messages
beginning with paride:, a protocol module's name or a driver's name) and
include that with your bug report. You can submit a bug report in one
of two ways. Either send it directly to the author of the PARIDE suite,
by e-mail to grant@torque.net, or join the linux-parport mailing list
and post your report there.
3.5 For more information or help
---------------------------------
You can join the linux-parport mailing list by sending a mail message
to:
linux-parport-request@torque.net
with the single word::
subscribe
in the body of the mail message (not in the subject line). Please be
sure that your mail program is correctly set up when you do this, as
the list manager is a robot that will subscribe you using the reply
address in your mail headers. REMOVE any anti-spam gimmicks you may
have in your mail headers, when sending mail to the list server.
You might also find some useful information on the linux-parport
web pages (although they are not always up to date) at
http://web.archive.org/web/%2E/http://www.torque.net/parport/

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==========================================
Using the RAM disk block device with Linux
==========================================
.. Contents:
1) Overview
2) Kernel Command Line Parameters
3) Using "rdev -r"
4) An Example of Creating a Compressed RAM Disk
1) Overview
-----------
The RAM disk driver is a way to use main system memory as a block device. It
is required for initrd, an initial filesystem used if you need to load modules
in order to access the root filesystem (see Documentation/admin-guide/initrd.rst). It can
also be used for a temporary filesystem for crypto work, since the contents
are erased on reboot.
The RAM disk dynamically grows as more space is required. It does this by using
RAM from the buffer cache. The driver marks the buffers it is using as dirty
so that the VM subsystem does not try to reclaim them later.
The RAM disk supports up to 16 RAM disks by default, and can be reconfigured
to support an unlimited number of RAM disks (at your own risk). Just change
the configuration symbol BLK_DEV_RAM_COUNT in the Block drivers config menu
and (re)build the kernel.
To use RAM disk support with your system, run './MAKEDEV ram' from the /dev
directory. RAM disks are all major number 1, and start with minor number 0
for /dev/ram0, etc. If used, modern kernels use /dev/ram0 for an initrd.
The new RAM disk also has the ability to load compressed RAM disk images,
allowing one to squeeze more programs onto an average installation or
rescue floppy disk.
2) Parameters
---------------------------------
2a) Kernel Command Line Parameters
ramdisk_size=N
Size of the ramdisk.
This parameter tells the RAM disk driver to set up RAM disks of N k size. The
default is 4096 (4 MB).
2b) Module parameters
rd_nr
/dev/ramX devices created.
max_part
Maximum partition number.
rd_size
See ramdisk_size.
3) Using "rdev -r"
------------------
The usage of the word (two bytes) that "rdev -r" sets in the kernel image is
as follows. The low 11 bits (0 -> 10) specify an offset (in 1 k blocks) of up
to 2 MB (2^11) of where to find the RAM disk (this used to be the size). Bit
14 indicates that a RAM disk is to be loaded, and bit 15 indicates whether a
prompt/wait sequence is to be given before trying to read the RAM disk. Since
the RAM disk dynamically grows as data is being written into it, a size field
is not required. Bits 11 to 13 are not currently used and may as well be zero.
These numbers are no magical secrets, as seen below::
./arch/x86/kernel/setup.c:#define RAMDISK_IMAGE_START_MASK 0x07FF
./arch/x86/kernel/setup.c:#define RAMDISK_PROMPT_FLAG 0x8000
./arch/x86/kernel/setup.c:#define RAMDISK_LOAD_FLAG 0x4000
Consider a typical two floppy disk setup, where you will have the
kernel on disk one, and have already put a RAM disk image onto disk #2.
Hence you want to set bits 0 to 13 as 0, meaning that your RAM disk
starts at an offset of 0 kB from the beginning of the floppy.
The command line equivalent is: "ramdisk_start=0"
You want bit 14 as one, indicating that a RAM disk is to be loaded.
The command line equivalent is: "load_ramdisk=1"
You want bit 15 as one, indicating that you want a prompt/keypress
sequence so that you have a chance to switch floppy disks.
The command line equivalent is: "prompt_ramdisk=1"
Putting that together gives 2^15 + 2^14 + 0 = 49152 for an rdev word.
So to create disk one of the set, you would do::
/usr/src/linux# cat arch/x86/boot/zImage > /dev/fd0
/usr/src/linux# rdev /dev/fd0 /dev/fd0
/usr/src/linux# rdev -r /dev/fd0 49152
If you make a boot disk that has LILO, then for the above, you would use::
append = "ramdisk_start=0 load_ramdisk=1 prompt_ramdisk=1"
Since the default start = 0 and the default prompt = 1, you could use::
append = "load_ramdisk=1"
4) An Example of Creating a Compressed RAM Disk
-----------------------------------------------
To create a RAM disk image, you will need a spare block device to
construct it on. This can be the RAM disk device itself, or an
unused disk partition (such as an unmounted swap partition). For this
example, we will use the RAM disk device, "/dev/ram0".
Note: This technique should not be done on a machine with less than 8 MB
of RAM. If using a spare disk partition instead of /dev/ram0, then this
restriction does not apply.
a) Decide on the RAM disk size that you want. Say 2 MB for this example.
Create it by writing to the RAM disk device. (This step is not currently
required, but may be in the future.) It is wise to zero out the
area (esp. for disks) so that maximal compression is achieved for
the unused blocks of the image that you are about to create::
dd if=/dev/zero of=/dev/ram0 bs=1k count=2048
b) Make a filesystem on it. Say ext2fs for this example::
mke2fs -vm0 /dev/ram0 2048
c) Mount it, copy the files you want to it (eg: /etc/* /dev/* ...)
and unmount it again.
d) Compress the contents of the RAM disk. The level of compression
will be approximately 50% of the space used by the files. Unused
space on the RAM disk will compress to almost nothing::
dd if=/dev/ram0 bs=1k count=2048 | gzip -v9 > /tmp/ram_image.gz
e) Put the kernel onto the floppy::
dd if=zImage of=/dev/fd0 bs=1k
f) Put the RAM disk image onto the floppy, after the kernel. Use an offset
that is slightly larger than the kernel, so that you can put another
(possibly larger) kernel onto the same floppy later without overlapping
the RAM disk image. An offset of 400 kB for kernels about 350 kB in
size would be reasonable. Make sure offset+size of ram_image.gz is
not larger than the total space on your floppy (usually 1440 kB)::
dd if=/tmp/ram_image.gz of=/dev/fd0 bs=1k seek=400
g) Use "rdev" to set the boot device, RAM disk offset, prompt flag, etc.
For prompt_ramdisk=1, load_ramdisk=1, ramdisk_start=400, one would
have 2^15 + 2^14 + 400 = 49552::
rdev /dev/fd0 /dev/fd0
rdev -r /dev/fd0 49552
That is it. You now have your boot/root compressed RAM disk floppy. Some
users may wish to combine steps (d) and (f) by using a pipe.
Paul Gortmaker 12/95
Changelog:
----------
10-22-04 :
Updated to reflect changes in command line options, remove
obsolete references, general cleanup.
James Nelson (james4765@gmail.com)
12-95 :
Original Document

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========================================
zram: Compressed RAM based block devices
========================================
Introduction
============
The zram module creates RAM based block devices named /dev/zram<id>
(<id> = 0, 1, ...). Pages written to these disks are compressed and stored
in memory itself. These disks allow very fast I/O and compression provides
good amounts of memory savings. Some of the usecases include /tmp storage,
use as swap disks, various caches under /var and maybe many more :)
Statistics for individual zram devices are exported through sysfs nodes at
/sys/block/zram<id>/
Usage
=====
There are several ways to configure and manage zram device(-s):
a) using zram and zram_control sysfs attributes
b) using zramctl utility, provided by util-linux (util-linux@vger.kernel.org).
In this document we will describe only 'manual' zram configuration steps,
IOW, zram and zram_control sysfs attributes.
In order to get a better idea about zramctl please consult util-linux
documentation, zramctl man-page or `zramctl --help`. Please be informed
that zram maintainers do not develop/maintain util-linux or zramctl, should
you have any questions please contact util-linux@vger.kernel.org
Following shows a typical sequence of steps for using zram.
WARNING
=======
For the sake of simplicity we skip error checking parts in most of the
examples below. However, it is your sole responsibility to handle errors.
zram sysfs attributes always return negative values in case of errors.
The list of possible return codes:
======== =============================================================
-EBUSY an attempt to modify an attribute that cannot be changed once
the device has been initialised. Please reset device first;
-ENOMEM zram was not able to allocate enough memory to fulfil your
needs;
-EINVAL invalid input has been provided.
======== =============================================================
If you use 'echo', the returned value that is changed by 'echo' utility,
and, in general case, something like::
echo 3 > /sys/block/zram0/max_comp_streams
if [ $? -ne 0 ];
handle_error
fi
should suffice.
1) Load Module
==============
::
modprobe zram num_devices=4
This creates 4 devices: /dev/zram{0,1,2,3}
num_devices parameter is optional and tells zram how many devices should be
pre-created. Default: 1.
2) Set max number of compression streams
========================================
Regardless the value passed to this attribute, ZRAM will always
allocate multiple compression streams - one per online CPUs - thus
allowing several concurrent compression operations. The number of
allocated compression streams goes down when some of the CPUs
become offline. There is no single-compression-stream mode anymore,
unless you are running a UP system or has only 1 CPU online.
To find out how many streams are currently available::
cat /sys/block/zram0/max_comp_streams
3) Select compression algorithm
===============================
Using comp_algorithm device attribute one can see available and
currently selected (shown in square brackets) compression algorithms,
change selected compression algorithm (once the device is initialised
there is no way to change compression algorithm).
Examples::
#show supported compression algorithms
cat /sys/block/zram0/comp_algorithm
lzo [lz4]
#select lzo compression algorithm
echo lzo > /sys/block/zram0/comp_algorithm
For the time being, the `comp_algorithm` content does not necessarily
show every compression algorithm supported by the kernel. We keep this
list primarily to simplify device configuration and one can configure
a new device with a compression algorithm that is not listed in
`comp_algorithm`. The thing is that, internally, ZRAM uses Crypto API
and, if some of the algorithms were built as modules, it's impossible
to list all of them using, for instance, /proc/crypto or any other
method. This, however, has an advantage of permitting the usage of
custom crypto compression modules (implementing S/W or H/W compression).
4) Set Disksize
===============
Set disk size by writing the value to sysfs node 'disksize'.
The value can be either in bytes or you can use mem suffixes.
Examples::
# Initialize /dev/zram0 with 50MB disksize
echo $((50*1024*1024)) > /sys/block/zram0/disksize
# Using mem suffixes
echo 256K > /sys/block/zram0/disksize
echo 512M > /sys/block/zram0/disksize
echo 1G > /sys/block/zram0/disksize
Note:
There is little point creating a zram of greater than twice the size of memory
since we expect a 2:1 compression ratio. Note that zram uses about 0.1% of the
size of the disk when not in use so a huge zram is wasteful.
5) Set memory limit: Optional
=============================
Set memory limit by writing the value to sysfs node 'mem_limit'.
The value can be either in bytes or you can use mem suffixes.
In addition, you could change the value in runtime.
Examples::
# limit /dev/zram0 with 50MB memory
echo $((50*1024*1024)) > /sys/block/zram0/mem_limit
# Using mem suffixes
echo 256K > /sys/block/zram0/mem_limit
echo 512M > /sys/block/zram0/mem_limit
echo 1G > /sys/block/zram0/mem_limit
# To disable memory limit
echo 0 > /sys/block/zram0/mem_limit
6) Activate
===========
::
mkswap /dev/zram0
swapon /dev/zram0
mkfs.ext4 /dev/zram1
mount /dev/zram1 /tmp
7) Add/remove zram devices
==========================
zram provides a control interface, which enables dynamic (on-demand) device
addition and removal.
In order to add a new /dev/zramX device, perform read operation on hot_add
attribute. This will return either new device's device id (meaning that you
can use /dev/zram<id>) or error code.
Example::
cat /sys/class/zram-control/hot_add
1
To remove the existing /dev/zramX device (where X is a device id)
execute::
echo X > /sys/class/zram-control/hot_remove
8) Stats
========
Per-device statistics are exported as various nodes under /sys/block/zram<id>/
A brief description of exported device attributes. For more details please
read Documentation/ABI/testing/sysfs-block-zram.
====================== ====== ===============================================
Name access description
====================== ====== ===============================================
disksize RW show and set the device's disk size
initstate RO shows the initialization state of the device
reset WO trigger device reset
mem_used_max WO reset the `mem_used_max` counter (see later)
mem_limit WO specifies the maximum amount of memory ZRAM can
use to store the compressed data
writeback_limit WO specifies the maximum amount of write IO zram
can write out to backing device as 4KB unit
writeback_limit_enable RW show and set writeback_limit feature
max_comp_streams RW the number of possible concurrent compress
operations
comp_algorithm RW show and change the compression algorithm
compact WO trigger memory compaction
debug_stat RO this file is used for zram debugging purposes
backing_dev RW set up backend storage for zram to write out
idle WO mark allocated slot as idle
====================== ====== ===============================================
User space is advised to use the following files to read the device statistics.
File /sys/block/zram<id>/stat
Represents block layer statistics. Read Documentation/block/stat.rst for
details.
File /sys/block/zram<id>/io_stat
The stat file represents device's I/O statistics not accounted by block
layer and, thus, not available in zram<id>/stat file. It consists of a
single line of text and contains the following stats separated by
whitespace:
============= =============================================================
failed_reads The number of failed reads
failed_writes The number of failed writes
invalid_io The number of non-page-size-aligned I/O requests
notify_free Depending on device usage scenario it may account
a) the number of pages freed because of swap slot free
notifications
b) the number of pages freed because of
REQ_OP_DISCARD requests sent by bio. The former ones are
sent to a swap block device when a swap slot is freed,
which implies that this disk is being used as a swap disk.
The latter ones are sent by filesystem mounted with
discard option, whenever some data blocks are getting
discarded.
============= =============================================================
File /sys/block/zram<id>/mm_stat
The stat file represents device's mm statistics. It consists of a single
line of text and contains the following stats separated by whitespace:
================ =============================================================
orig_data_size uncompressed size of data stored in this disk.
This excludes same-element-filled pages (same_pages) since
no memory is allocated for them.
Unit: bytes
compr_data_size compressed size of data stored in this disk
mem_used_total the amount of memory allocated for this disk. This
includes allocator fragmentation and metadata overhead,
allocated for this disk. So, allocator space efficiency
can be calculated using compr_data_size and this statistic.
Unit: bytes
mem_limit the maximum amount of memory ZRAM can use to store
the compressed data
mem_used_max the maximum amount of memory zram have consumed to
store the data
same_pages the number of same element filled pages written to this disk.
No memory is allocated for such pages.
pages_compacted the number of pages freed during compaction
huge_pages the number of incompressible pages
================ =============================================================
File /sys/block/zram<id>/bd_stat
The stat file represents device's backing device statistics. It consists of
a single line of text and contains the following stats separated by whitespace:
============== =============================================================
bd_count size of data written in backing device.
Unit: 4K bytes
bd_reads the number of reads from backing device
Unit: 4K bytes
bd_writes the number of writes to backing device
Unit: 4K bytes
============== =============================================================
9) Deactivate
=============
::
swapoff /dev/zram0
umount /dev/zram1
10) Reset
=========
Write any positive value to 'reset' sysfs node::
echo 1 > /sys/block/zram0/reset
echo 1 > /sys/block/zram1/reset
This frees all the memory allocated for the given device and
resets the disksize to zero. You must set the disksize again
before reusing the device.
Optional Feature
================
writeback
---------
With CONFIG_ZRAM_WRITEBACK, zram can write idle/incompressible page
to backing storage rather than keeping it in memory.
To use the feature, admin should set up backing device via::
echo /dev/sda5 > /sys/block/zramX/backing_dev
before disksize setting. It supports only partition at this moment.
If admin want to use incompressible page writeback, they could do via::
echo huge > /sys/block/zramX/write
To use idle page writeback, first, user need to declare zram pages
as idle::
echo all > /sys/block/zramX/idle
From now on, any pages on zram are idle pages. The idle mark
will be removed until someone request access of the block.
IOW, unless there is access request, those pages are still idle pages.
Admin can request writeback of those idle pages at right timing via::
echo idle > /sys/block/zramX/writeback
With the command, zram writeback idle pages from memory to the storage.
If there are lots of write IO with flash device, potentially, it has
flash wearout problem so that admin needs to design write limitation
to guarantee storage health for entire product life.
To overcome the concern, zram supports "writeback_limit" feature.
The "writeback_limit_enable"'s default value is 0 so that it doesn't limit
any writeback. IOW, if admin want to apply writeback budget, he should
enable writeback_limit_enable via::
$ echo 1 > /sys/block/zramX/writeback_limit_enable
Once writeback_limit_enable is set, zram doesn't allow any writeback
until admin set the budget via /sys/block/zramX/writeback_limit.
(If admin doesn't enable writeback_limit_enable, writeback_limit's value
assigned via /sys/block/zramX/writeback_limit is meaninless.)
If admin want to limit writeback as per-day 400M, he could do it
like below::
$ MB_SHIFT=20
$ 4K_SHIFT=12
$ echo $((400<<MB_SHIFT>>4K_SHIFT)) > \
/sys/block/zram0/writeback_limit.
$ echo 1 > /sys/block/zram0/writeback_limit_enable
If admin want to allow further write again once the bugdet is exausted,
he could do it like below::
$ echo $((400<<MB_SHIFT>>4K_SHIFT)) > \
/sys/block/zram0/writeback_limit
If admin want to see remaining writeback budget since he set::
$ cat /sys/block/zramX/writeback_limit
If admin want to disable writeback limit, he could do::
$ echo 0 > /sys/block/zramX/writeback_limit_enable
The writeback_limit count will reset whenever you reset zram(e.g.,
system reboot, echo 1 > /sys/block/zramX/reset) so keeping how many of
writeback happened until you reset the zram to allocate extra writeback
budget in next setting is user's job.
If admin want to measure writeback count in a certain period, he could
know it via /sys/block/zram0/bd_stat's 3rd column.
memory tracking
===============
With CONFIG_ZRAM_MEMORY_TRACKING, user can know information of the
zram block. It could be useful to catch cold or incompressible
pages of the process with*pagemap.
If you enable the feature, you could see block state via
/sys/kernel/debug/zram/zram0/block_state". The output is as follows::
300 75.033841 .wh.
301 63.806904 s...
302 63.806919 ..hi
First column
zram's block index.
Second column
access time since the system was booted
Third column
state of the block:
s:
same page
w:
written page to backing store
h:
huge page
i:
idle page
First line of above example says 300th block is accessed at 75.033841sec
and the block's state is huge so it is written back to the backing
storage. It's a debugging feature so anyone shouldn't rely on it to work
properly.
Nitin Gupta
ngupta@vflare.org