diff options
Diffstat (limited to 'Documentation/blockdev')
| -rw-r--r-- | Documentation/blockdev/drbd/data-structure-v9.txt | 38 | ||||
| -rw-r--r-- | Documentation/blockdev/zram.txt | 54 |
2 files changed, 86 insertions, 6 deletions
diff --git a/Documentation/blockdev/drbd/data-structure-v9.txt b/Documentation/blockdev/drbd/data-structure-v9.txt new file mode 100644 index 000000000000..1e52a0e32624 --- /dev/null +++ b/Documentation/blockdev/drbd/data-structure-v9.txt @@ -0,0 +1,38 @@ +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. diff --git a/Documentation/blockdev/zram.txt b/Documentation/blockdev/zram.txt index 2eccddffa6c8..0595c3f56ccf 100644 --- a/Documentation/blockdev/zram.txt +++ b/Documentation/blockdev/zram.txt @@ -21,7 +21,43 @@ Following shows a typical sequence of steps for using zram. This creates 4 devices: /dev/zram{0,1,2,3} (num_devices parameter is optional. Default: 1) -2) Set Disksize +2) Set max number of compression streams + Compression backend may use up to max_comp_streams compression streams, + thus allowing up to max_comp_streams concurrent compression operations. + By default, compression backend uses single compression stream. + + Examples: + #show max compression streams number + cat /sys/block/zram0/max_comp_streams + + #set max compression streams number to 3 + echo 3 > /sys/block/zram0/max_comp_streams + +Note: +In order to enable compression backend's multi stream support max_comp_streams +must be initially set to desired concurrency level before ZRAM device +initialisation. Once the device initialised as a single stream compression +backend (max_comp_streams equals to 1), you will see error if you try to change +the value of max_comp_streams because single stream compression backend +implemented as a special case by lock overhead issue and does not support +dynamic max_comp_streams. Only multi stream backend supports dynamic +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, + 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 + +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: @@ -33,32 +69,38 @@ Following shows a typical sequence of steps for using zram. echo 512M > /sys/block/zram0/disksize echo 1G > /sys/block/zram0/disksize -3) Activate: +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) Activate: mkswap /dev/zram0 swapon /dev/zram0 mkfs.ext4 /dev/zram1 mount /dev/zram1 /tmp -4) Stats: +6) Stats: Per-device statistics are exported as various nodes under /sys/block/zram<id>/ disksize num_reads num_writes + failed_reads + failed_writes invalid_io notify_free - discard zero_pages orig_data_size compr_data_size mem_used_total -5) Deactivate: +7) Deactivate: swapoff /dev/zram0 umount /dev/zram1 -6) Reset: +8) Reset: Write any positive value to 'reset' sysfs node echo 1 > /sys/block/zram0/reset echo 1 > /sys/block/zram1/reset |