Merge remote-tracking branch 'nvdimm/libnvdimm-for-next'

[karo-tx-linux.git] / Documentation / blockdev / zram.txt

diff --git a/Documentation/blockdev/zram.txt b/Documentation/blockdev/zram.txt
index 62435bb252660f0e870e71f0f7f3f6ae0449d397..5bda5031c83de2b6e85ff2a6fe8bb3a8107a4aa5 100644 (file)
--- 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
 
 
 * 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.
 
 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}
 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
 
 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).
 
        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>/
 
 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
 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
 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
 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