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Diffstat (limited to 'kernel/Documentation/blockdev/zram.txt')
| -rw-r--r-- | kernel/Documentation/blockdev/zram.txt | 76 |
1 files changed, 66 insertions, 10 deletions
diff --git a/kernel/Documentation/blockdev/zram.txt b/kernel/Documentation/blockdev/zram.txt index 48a183e29..5bda5031c 100644 --- a/kernel/Documentation/blockdev/zram.txt +++ b/kernel/Documentation/blockdev/zram.txt @@ -14,12 +14,49 @@ 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@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. Default: 1) + +num_devices parameter is optional and tells zram how many devices should be +pre-created. Default: 1. 2) Set max number of compression streams Compression backend may use up to max_comp_streams compression streams, @@ -45,7 +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). @@ -97,10 +134,27 @@ size of the disk when not in use so a huge zram is wasteful. mkfs.ext4 /dev/zram1 mount /dev/zram1 /tmp -7) Stats: +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 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 @@ -121,12 +175,14 @@ 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 -num_migrated RO the number of objects migrated migrated by compaction - +pages_compacted RO the number of pages freed during compaction + (available only via zram<id>/mm_stat node) +compact WO trigger memory compaction WARNING ======= @@ -172,11 +228,11 @@ line of text and contains the following stats separated by whitespace: zero_pages num_migrated -8) Deactivate: +9) Deactivate: swapoff /dev/zram0 umount /dev/zram1 -9) Reset: +10) Reset: Write any positive value to 'reset' sysfs node echo 1 > /sys/block/zram0/reset echo 1 > /sys/block/zram1/reset |