projects / GitHub / mt8127 / android_kernel_alcatel_ttab.git / blame
| Commit | Line | Data |
|---|---|---|
| 00ac9ba0 NG |
1 | zram: Compressed RAM based block devices |
| 2 | ---------------------------------------- | |
| 47f9afb3 NG |
3 | |
| 4 | Project home: http://compcache.googlecode.com/ | |
| 5 | ||
| 6 | * Introduction | |
| 7 | ||
| 9b9913d8 NG |
8 | The zram module creates RAM based block devices named /dev/zram<id> |
| 9 | (<id> = 0, 1, ...). Pages written to these disks are compressed and stored | |
| 10 | in memory itself. These disks allow very fast I/O and compression provides | |
| 11 | good amounts of memory savings. Some of the usecases include /tmp storage, | |
| 12 | use as swap disks, various caches under /var and maybe many more :) | |
| 47f9afb3 | 13 | |
| 9b9913d8 NG |
14 | Statistics for individual zram devices are exported through sysfs nodes at |
| 15 | /sys/block/zram<id>/ | |
| 47f9afb3 NG |
16 | |
| 17 | * Usage | |
| 18 | ||
| 00ac9ba0 | 19 | Following shows a typical sequence of steps for using zram. |
| 47f9afb3 | 20 | |
| 9b9913d8 | 21 | 1) Load Module: |
| 00ac9ba0 | 22 | modprobe zram num_devices=4 |
| 9b9913d8 | 23 | This creates 4 devices: /dev/zram{0,1,2,3} |
| 47f9afb3 NG |
24 | (num_devices parameter is optional. Default: 1) |
| 25 | ||
| 9b9913d8 NG |
26 | 2) Set Disksize (Optional): |
| 27 | Set disk size by writing the value to sysfs node 'disksize' | |
| 28 | (in bytes). If disksize is not given, default value of 25% | |
| 29 | of RAM is used. | |
| 30 | ||
| 31 | # Initialize /dev/zram0 with 50MB disksize | |
| 32 | echo $((50*1024*1024)) > /sys/block/zram0/disksize | |
| 47f9afb3 | 33 | |
| 9b9913d8 NG |
34 | NOTE: disksize cannot be changed if the disk contains any |
| 35 | data. So, for such a disk, you need to issue 'reset' (see below) | |
| 36 | before you can change its disksize. | |
| 47f9afb3 NG |
37 | |
| 38 | 3) Activate: | |
| 00ac9ba0 NG |
39 | mkswap /dev/zram0 |
| 40 | swapon /dev/zram0 | |
| 41 | ||
| 42 | mkfs.ext4 /dev/zram1 | |
| 43 | mount /dev/zram1 /tmp | |
| 47f9afb3 NG |
44 | |
| 45 | 4) Stats: | |
| 9b9913d8 NG |
46 | Per-device statistics are exported as various nodes under |
| 47 | /sys/block/zram<id>/ | |
| 48 | disksize | |
| 49 | num_reads | |
| 50 | num_writes | |
| 51 | invalid_io | |
| 52 | notify_free | |
| 53 | discard | |
| 54 | zero_pages | |
| 55 | orig_data_size | |
| 56 | compr_data_size | |
| 57 | mem_used_total | |
| 47f9afb3 NG |
58 | |
| 59 | 5) Deactivate: | |
| 00ac9ba0 NG |
60 | swapoff /dev/zram0 |
| 61 | umount /dev/zram1 | |
| 47f9afb3 NG |
62 | |
| 63 | 6) Reset: | |
| 9b9913d8 NG |
64 | Write any positive value to 'reset' sysfs node |
| 65 | echo 1 > /sys/block/zram0/reset | |
| 66 | echo 1 > /sys/block/zram1/reset | |
| 67 | ||
| 68 | (This frees all the memory allocated for the given device). | |
| 47f9afb3 NG |
69 | |
| 70 | ||
| 71 | Please report any problems at: | |
| 72 | - Mailing list: linux-mm-cc at laptop dot org | |
| 73 | - Issue tracker: http://code.google.com/p/compcache/issues/list | |
| 74 | ||
| 75 | Nitin Gupta | |
| 76 | ngupta@vflare.org |