[PATCHv2] zram: update documentation

From: Sergey Senozhatsky
Date: Thu Sep 24 2015 - 05:57:59 EST

From: Sergey SENOZHATSKY <sergey.senozhatsky@xxxxxxxxx>

Several documentation changes.

First, we never mentioned any errors and never required any
error checks in documentation.

Second, mention that there is another way to configure and
manage zram devices -- zramctl, provided by util-linux.

Third, add a bit of clarification on why `mem_used_max' attr
is RW and correct some typos.

Signed-off-by: Sergey Senozhatsky <sergey.senozhatsky@xxxxxxxxx>
Documentation/blockdev/zram.txt | 44 +++++++++++++++++++++++++++++++++++++----
1 file changed, 40 insertions(+), 4 deletions(-)

diff --git a/Documentation/blockdev/zram.txt b/Documentation/blockdev/zram.txt
index 62435bb..5bda503 100644
--- a/Documentation/blockdev/zram.txt
+++ b/Documentation/blockdev/zram.txt
@@ -14,8 +14,43 @@ Statistics for individual zram devices are exported through sysfs nodes at

* 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@xxxxxxxxxxxxxxx).
+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@xxxxxxxxxxxxxxx
Following shows a typical sequence of steps for using zram.

+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
+-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}
@@ -47,7 +82,7 @@ max_comp_streams adjustment.

3) Select compression algorithm
Using comp_algorithm device attribute one can see available and
- currently selected (shown in square brackets) compression algortithms,
+ 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).

@@ -119,7 +154,7 @@ execute
8) Stats:
Per-device statistics are exported as various nodes under /sys/block/zram<id>/

-A brief description of exported device attritbutes. For more details please
+A brief description of exported device attributes. For more details please
read Documentation/ABI/testing/sysfs-block-zram.

Name access description
@@ -140,8 +175,9 @@ zero_pages RO the number of zero filled pages written to this disk
orig_data_size RO uncompressed size of data stored in this disk
compr_data_size RO compressed size of data stored in this disk
mem_used_total RO the amount of memory allocated for this disk
-mem_used_max RW the maximum amount memory zram have consumed to
- store compressed data
+mem_used_max RW the maximum amount of memory zram have consumed to
+ store the data (to reset this counter to the actual
+ current value, write 1 to this attribute)
mem_limit RW the maximum amount of memory ZRAM can use to store
the compressed data
pages_compacted RO the number of pages freed during compaction

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