Nitin Gupta | 00ac9ba | 2010-06-01 13:31:26 +0530 | [diff] [blame] | 1 | zram: Compressed RAM based block devices |
| 2 | ---------------------------------------- |
Nitin Gupta | 47f9afb | 2009-09-22 10:26:54 +0530 | [diff] [blame] | 3 | |
Nitin Gupta | 47f9afb | 2009-09-22 10:26:54 +0530 | [diff] [blame] | 4 | * Introduction |
| 5 | |
Nitin Gupta | 9b9913d | 2010-08-09 22:56:55 +0530 | [diff] [blame] | 6 | The zram module creates RAM based block devices named /dev/zram<id> |
| 7 | (<id> = 0, 1, ...). Pages written to these disks are compressed and stored |
| 8 | in memory itself. These disks allow very fast I/O and compression provides |
| 9 | good amounts of memory savings. Some of the usecases include /tmp storage, |
| 10 | use as swap disks, various caches under /var and maybe many more :) |
Nitin Gupta | 47f9afb | 2009-09-22 10:26:54 +0530 | [diff] [blame] | 11 | |
Nitin Gupta | 9b9913d | 2010-08-09 22:56:55 +0530 | [diff] [blame] | 12 | Statistics for individual zram devices are exported through sysfs nodes at |
| 13 | /sys/block/zram<id>/ |
Nitin Gupta | 47f9afb | 2009-09-22 10:26:54 +0530 | [diff] [blame] | 14 | |
| 15 | * Usage |
| 16 | |
Nitin Gupta | 00ac9ba | 2010-06-01 13:31:26 +0530 | [diff] [blame] | 17 | Following shows a typical sequence of steps for using zram. |
Nitin Gupta | 47f9afb | 2009-09-22 10:26:54 +0530 | [diff] [blame] | 18 | |
Nitin Gupta | 9b9913d | 2010-08-09 22:56:55 +0530 | [diff] [blame] | 19 | 1) Load Module: |
Nitin Gupta | 00ac9ba | 2010-06-01 13:31:26 +0530 | [diff] [blame] | 20 | modprobe zram num_devices=4 |
Nitin Gupta | 9b9913d | 2010-08-09 22:56:55 +0530 | [diff] [blame] | 21 | This creates 4 devices: /dev/zram{0,1,2,3} |
Nitin Gupta | 47f9afb | 2009-09-22 10:26:54 +0530 | [diff] [blame] | 22 | (num_devices parameter is optional. Default: 1) |
| 23 | |
Sergey Senozhatsky | beca3ec | 2014-04-07 15:38:14 -0700 | [diff] [blame^] | 24 | 2) Set max number of compression streams |
| 25 | Compression backend may use up to max_comp_streams compression streams, |
| 26 | thus allowing up to max_comp_streams concurrent compression operations. |
| 27 | By default, compression backend uses single compression stream. |
| 28 | |
| 29 | Examples: |
| 30 | #show max compression streams number |
| 31 | cat /sys/block/zram0/max_comp_streams |
| 32 | |
| 33 | #set max compression streams number to 3 |
| 34 | echo 3 > /sys/block/zram0/max_comp_streams |
| 35 | |
| 36 | Note: |
| 37 | In order to enable compression backend's multi stream support max_comp_streams |
| 38 | must be initially set to desired concurrency level before ZRAM device |
| 39 | initialisation. Once the device initialised as a single stream compression |
| 40 | backend (max_comp_streams equals to 0) changing the value of max_comp_streams |
| 41 | will not take any effect, because single stream compression backend implemented |
| 42 | as a special case and does not support dynamic max_comp_streams. Only multi |
| 43 | stream backend supports dynamic max_comp_streams adjustment. |
| 44 | |
| 45 | 3) Set Disksize |
Minchan Kim | 0231c40 | 2013-01-30 11:41:40 +0900 | [diff] [blame] | 46 | Set disk size by writing the value to sysfs node 'disksize'. |
| 47 | The value can be either in bytes or you can use mem suffixes. |
| 48 | Examples: |
| 49 | # Initialize /dev/zram0 with 50MB disksize |
| 50 | echo $((50*1024*1024)) > /sys/block/zram0/disksize |
Nitin Gupta | 47f9afb | 2009-09-22 10:26:54 +0530 | [diff] [blame] | 51 | |
Minchan Kim | 0231c40 | 2013-01-30 11:41:40 +0900 | [diff] [blame] | 52 | # Using mem suffixes |
| 53 | echo 256K > /sys/block/zram0/disksize |
| 54 | echo 512M > /sys/block/zram0/disksize |
| 55 | echo 1G > /sys/block/zram0/disksize |
Nitin Gupta | 47f9afb | 2009-09-22 10:26:54 +0530 | [diff] [blame] | 56 | |
Sergey Senozhatsky | e64cd51 | 2014-04-07 15:38:07 -0700 | [diff] [blame] | 57 | Note: |
| 58 | There is little point creating a zram of greater than twice the size of memory |
| 59 | since we expect a 2:1 compression ratio. Note that zram uses about 0.1% of the |
| 60 | size of the disk when not in use so a huge zram is wasteful. |
| 61 | |
Sergey Senozhatsky | beca3ec | 2014-04-07 15:38:14 -0700 | [diff] [blame^] | 62 | 4) Activate: |
Nitin Gupta | 00ac9ba | 2010-06-01 13:31:26 +0530 | [diff] [blame] | 63 | mkswap /dev/zram0 |
| 64 | swapon /dev/zram0 |
| 65 | |
| 66 | mkfs.ext4 /dev/zram1 |
| 67 | mount /dev/zram1 /tmp |
Nitin Gupta | 47f9afb | 2009-09-22 10:26:54 +0530 | [diff] [blame] | 68 | |
Sergey Senozhatsky | beca3ec | 2014-04-07 15:38:14 -0700 | [diff] [blame^] | 69 | 5) Stats: |
Nitin Gupta | 9b9913d | 2010-08-09 22:56:55 +0530 | [diff] [blame] | 70 | Per-device statistics are exported as various nodes under |
| 71 | /sys/block/zram<id>/ |
| 72 | disksize |
| 73 | num_reads |
| 74 | num_writes |
Sergey Senozhatsky | 8dd1d32 | 2014-04-07 15:38:08 -0700 | [diff] [blame] | 75 | failed_reads |
| 76 | failed_writes |
Nitin Gupta | 9b9913d | 2010-08-09 22:56:55 +0530 | [diff] [blame] | 77 | invalid_io |
| 78 | notify_free |
Nitin Gupta | 9b9913d | 2010-08-09 22:56:55 +0530 | [diff] [blame] | 79 | zero_pages |
| 80 | orig_data_size |
| 81 | compr_data_size |
| 82 | mem_used_total |
Nitin Gupta | 47f9afb | 2009-09-22 10:26:54 +0530 | [diff] [blame] | 83 | |
Sergey Senozhatsky | beca3ec | 2014-04-07 15:38:14 -0700 | [diff] [blame^] | 84 | 6) Deactivate: |
Nitin Gupta | 00ac9ba | 2010-06-01 13:31:26 +0530 | [diff] [blame] | 85 | swapoff /dev/zram0 |
| 86 | umount /dev/zram1 |
Nitin Gupta | 47f9afb | 2009-09-22 10:26:54 +0530 | [diff] [blame] | 87 | |
Sergey Senozhatsky | beca3ec | 2014-04-07 15:38:14 -0700 | [diff] [blame^] | 88 | 7) Reset: |
Nitin Gupta | 9b9913d | 2010-08-09 22:56:55 +0530 | [diff] [blame] | 89 | Write any positive value to 'reset' sysfs node |
| 90 | echo 1 > /sys/block/zram0/reset |
| 91 | echo 1 > /sys/block/zram1/reset |
| 92 | |
Minchan Kim | 0231c40 | 2013-01-30 11:41:40 +0900 | [diff] [blame] | 93 | This frees all the memory allocated for the given device and |
| 94 | resets the disksize to zero. You must set the disksize again |
| 95 | before reusing the device. |
Nitin Gupta | 47f9afb | 2009-09-22 10:26:54 +0530 | [diff] [blame] | 96 | |
Nitin Gupta | 47f9afb | 2009-09-22 10:26:54 +0530 | [diff] [blame] | 97 | Nitin Gupta |
| 98 | ngupta@vflare.org |