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Diffstat (limited to 'Documentation/blockdev/zram.txt')
| -rw-r--r-- | Documentation/blockdev/zram.txt | 82 |
1 files changed, 46 insertions, 36 deletions
diff --git a/Documentation/blockdev/zram.txt b/Documentation/blockdev/zram.txt index 13100fb3c26d..0535ae1f73e5 100644 --- a/Documentation/blockdev/zram.txt +++ b/Documentation/blockdev/zram.txt @@ -59,23 +59,23 @@ num_devices parameter is optional and tells zram how many devices should be pre-created. Default: 1. 2) Set max number of compression streams - Regardless the value passed to this attribute, ZRAM will always - allocate multiple compression streams - one per online CPUs - thus - allowing several concurrent compression operations. The number of - allocated compression streams goes down when some of the CPUs - become offline. There is no single-compression-stream mode anymore, - unless you are running a UP system or has only 1 CPU online. - - To find out how many streams are currently available: +Regardless the value passed to this attribute, ZRAM will always +allocate multiple compression streams - one per online CPUs - thus +allowing several concurrent compression operations. The number of +allocated compression streams goes down when some of the CPUs +become offline. There is no single-compression-stream mode anymore, +unless you are running a UP system or has only 1 CPU online. + +To find out how many streams are currently available: cat /sys/block/zram0/max_comp_streams 3) Select compression algorithm - Using comp_algorithm device attribute one can see available and - 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). +Using comp_algorithm device attribute one can see available and +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). - Examples: +Examples: #show supported compression algorithms cat /sys/block/zram0/comp_algorithm lzo [lz4] @@ -83,17 +83,27 @@ pre-created. Default: 1. #select lzo compression algorithm echo lzo > /sys/block/zram0/comp_algorithm +For the time being, the `comp_algorithm' content does not necessarily +show every compression algorithm supported by the kernel. We keep this +list primarily to simplify device configuration and one can configure +a new device with a compression algorithm that is not listed in +`comp_algorithm'. The thing is that, internally, ZRAM uses Crypto API +and, if some of the algorithms were built as modules, it's impossible +to list all of them using, for instance, /proc/crypto or any other +method. This, however, has an advantage of permitting the usage of +custom crypto compression modules (implementing S/W or H/W compression). + 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: - # Initialize /dev/zram0 with 50MB disksize - echo $((50*1024*1024)) > /sys/block/zram0/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: + # Initialize /dev/zram0 with 50MB disksize + echo $((50*1024*1024)) > /sys/block/zram0/disksize - # Using mem suffixes - echo 256K > /sys/block/zram0/disksize - echo 512M > /sys/block/zram0/disksize - echo 1G > /sys/block/zram0/disksize + # Using mem suffixes + echo 256K > /sys/block/zram0/disksize + echo 512M > /sys/block/zram0/disksize + echo 1G > /sys/block/zram0/disksize Note: There is little point creating a zram of greater than twice the size of memory @@ -101,20 +111,20 @@ 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) Set memory limit: Optional - Set memory limit by writing the value to sysfs node 'mem_limit'. - The value can be either in bytes or you can use mem suffixes. - In addition, you could change the value in runtime. - Examples: - # limit /dev/zram0 with 50MB memory - echo $((50*1024*1024)) > /sys/block/zram0/mem_limit - - # Using mem suffixes - echo 256K > /sys/block/zram0/mem_limit - echo 512M > /sys/block/zram0/mem_limit - echo 1G > /sys/block/zram0/mem_limit - - # To disable memory limit - echo 0 > /sys/block/zram0/mem_limit +Set memory limit by writing the value to sysfs node 'mem_limit'. +The value can be either in bytes or you can use mem suffixes. +In addition, you could change the value in runtime. +Examples: + # limit /dev/zram0 with 50MB memory + echo $((50*1024*1024)) > /sys/block/zram0/mem_limit + + # Using mem suffixes + echo 256K > /sys/block/zram0/mem_limit + echo 512M > /sys/block/zram0/mem_limit + echo 1G > /sys/block/zram0/mem_limit + + # To disable memory limit + echo 0 > /sys/block/zram0/mem_limit 6) Activate: mkswap /dev/zram0 |