^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 1) ========================================
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 2) zram: Compressed RAM-based block devices
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 3) ========================================
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 4)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 5) Introduction
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 6) ============
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 7)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 8) The zram module creates RAM-based block devices named /dev/zram<id>
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 9) (<id> = 0, 1, ...). Pages written to these disks are compressed and stored
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 10) in memory itself. These disks allow very fast I/O and compression provides
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 11) good amounts of memory savings. Some of the use cases include /tmp storage,
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 12) use as swap disks, various caches under /var and maybe many more. :)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 13)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 14) Statistics for individual zram devices are exported through sysfs nodes at
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 15) /sys/block/zram<id>/
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 16)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 17) Usage
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 18) =====
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 19)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 20) There are several ways to configure and manage zram device(-s):
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 21)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 22) a) using zram and zram_control sysfs attributes
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 23) b) using zramctl utility, provided by util-linux (util-linux@vger.kernel.org).
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 24)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 25) In this document we will describe only 'manual' zram configuration steps,
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 26) IOW, zram and zram_control sysfs attributes.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 27)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 28) In order to get a better idea about zramctl please consult util-linux
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 29) documentation, zramctl man-page or `zramctl --help`. Please be informed
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 30) that zram maintainers do not develop/maintain util-linux or zramctl, should
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 31) you have any questions please contact util-linux@vger.kernel.org
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 32)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 33) Following shows a typical sequence of steps for using zram.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 34)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 35) WARNING
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 36) =======
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 37)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 38) For the sake of simplicity we skip error checking parts in most of the
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 39) examples below. However, it is your sole responsibility to handle errors.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 40)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 41) zram sysfs attributes always return negative values in case of errors.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 42) The list of possible return codes:
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 43)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 44) ======== =============================================================
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 45) -EBUSY an attempt to modify an attribute that cannot be changed once
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 46) the device has been initialised. Please reset device first.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 47) -ENOMEM zram was not able to allocate enough memory to fulfil your
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 48) needs.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 49) -EINVAL invalid input has been provided.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 50) ======== =============================================================
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 51)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 52) If you use 'echo', the returned value is set by the 'echo' utility,
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 53) and, in general case, something like::
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 54)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 55) echo 3 > /sys/block/zram0/max_comp_streams
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 56) if [ $? -ne 0 ]; then
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 57) handle_error
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 58) fi
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 59)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 60) should suffice.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 61)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 62) 1) Load Module
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 63) ==============
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 64)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 65) ::
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 66)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 67) modprobe zram num_devices=4
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 68)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 69) This creates 4 devices: /dev/zram{0,1,2,3}
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 70)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 71) num_devices parameter is optional and tells zram how many devices should be
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 72) pre-created. Default: 1.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 73)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 74) 2) Set max number of compression streams
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 75) ========================================
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 76)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 77) Regardless of the value passed to this attribute, ZRAM will always
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 78) allocate multiple compression streams - one per online CPU - thus
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 79) allowing several concurrent compression operations. The number of
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 80) allocated compression streams goes down when some of the CPUs
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 81) become offline. There is no single-compression-stream mode anymore,
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 82) unless you are running a UP system or have only 1 CPU online.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 83)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 84) To find out how many streams are currently available::
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 85)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 86) cat /sys/block/zram0/max_comp_streams
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 87)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 88) 3) Select compression algorithm
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 89) ===============================
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 90)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 91) Using comp_algorithm device attribute one can see available and
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 92) currently selected (shown in square brackets) compression algorithms,
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 93) or change the selected compression algorithm (once the device is initialised
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 94) there is no way to change compression algorithm).
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 95)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 96) Examples::
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 97)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 98) #show supported compression algorithms
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 99) cat /sys/block/zram0/comp_algorithm
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 100) lzo [lz4]
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 101)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 102) #select lzo compression algorithm
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 103) echo lzo > /sys/block/zram0/comp_algorithm
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 104)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 105) For the time being, the `comp_algorithm` content does not necessarily
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 106) show every compression algorithm supported by the kernel. We keep this
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 107) list primarily to simplify device configuration and one can configure
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 108) a new device with a compression algorithm that is not listed in
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 109) `comp_algorithm`. The thing is that, internally, ZRAM uses Crypto API
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 110) and, if some of the algorithms were built as modules, it's impossible
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 111) to list all of them using, for instance, /proc/crypto or any other
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 112) method. This, however, has an advantage of permitting the usage of
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 113) custom crypto compression modules (implementing S/W or H/W compression).
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 114)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 115) 4) Set Disksize
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 116) ===============
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 117)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 118) Set disk size by writing the value to sysfs node 'disksize'.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 119) The value can be either in bytes or you can use mem suffixes.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 120) Examples::
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 121)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 122) # Initialize /dev/zram0 with 50MB disksize
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 123) echo $((50*1024*1024)) > /sys/block/zram0/disksize
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 124)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 125) # Using mem suffixes
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 126) echo 256K > /sys/block/zram0/disksize
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 127) echo 512M > /sys/block/zram0/disksize
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 128) echo 1G > /sys/block/zram0/disksize
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 129)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 130) Note:
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 131) There is little point creating a zram of greater than twice the size of memory
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 132) since we expect a 2:1 compression ratio. Note that zram uses about 0.1% of the
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 133) size of the disk when not in use so a huge zram is wasteful.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 134)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 135) 5) Set memory limit: Optional
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 136) =============================
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 137)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 138) Set memory limit by writing the value to sysfs node 'mem_limit'.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 139) The value can be either in bytes or you can use mem suffixes.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 140) In addition, you could change the value in runtime.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 141) Examples::
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 142)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 143) # limit /dev/zram0 with 50MB memory
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 144) echo $((50*1024*1024)) > /sys/block/zram0/mem_limit
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 145)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 146) # Using mem suffixes
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 147) echo 256K > /sys/block/zram0/mem_limit
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 148) echo 512M > /sys/block/zram0/mem_limit
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 149) echo 1G > /sys/block/zram0/mem_limit
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 150)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 151) # To disable memory limit
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 152) echo 0 > /sys/block/zram0/mem_limit
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 153)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 154) 6) Activate
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 155) ===========
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 156)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 157) ::
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 158)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 159) mkswap /dev/zram0
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 160) swapon /dev/zram0
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 161)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 162) mkfs.ext4 /dev/zram1
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 163) mount /dev/zram1 /tmp
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 164)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 165) 7) Add/remove zram devices
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 166) ==========================
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 167)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 168) zram provides a control interface, which enables dynamic (on-demand) device
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 169) addition and removal.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 170)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 171) In order to add a new /dev/zramX device, perform a read operation on the hot_add
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 172) attribute. This will return either the new device's device id (meaning that you
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 173) can use /dev/zram<id>) or an error code.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 174)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 175) Example::
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 176)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 177) cat /sys/class/zram-control/hot_add
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 178) 1
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 179)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 180) To remove the existing /dev/zramX device (where X is a device id)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 181) execute::
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 182)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 183) echo X > /sys/class/zram-control/hot_remove
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 184)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 185) 8) Stats
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 186) ========
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 187)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 188) Per-device statistics are exported as various nodes under /sys/block/zram<id>/
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 189)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 190) A brief description of exported device attributes follows. For more details
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 191) please read Documentation/ABI/testing/sysfs-block-zram.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 192)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 193) ====================== ====== ===============================================
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 194) Name access description
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 195) ====================== ====== ===============================================
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 196) disksize RW show and set the device's disk size
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 197) initstate RO shows the initialization state of the device
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 198) reset WO trigger device reset
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 199) mem_used_max WO reset the `mem_used_max` counter (see later)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 200) mem_limit WO specifies the maximum amount of memory ZRAM can
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 201) use to store the compressed data
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 202) writeback_limit WO specifies the maximum amount of write IO zram
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 203) can write out to backing device as 4KB unit
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 204) writeback_limit_enable RW show and set writeback_limit feature
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 205) max_comp_streams RW the number of possible concurrent compress
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 206) operations
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 207) comp_algorithm RW show and change the compression algorithm
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 208) compact WO trigger memory compaction
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 209) debug_stat RO this file is used for zram debugging purposes
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 210) backing_dev RW set up backend storage for zram to write out
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 211) idle WO mark allocated slot as idle
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 212) ====================== ====== ===============================================
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 213)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 214)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 215) User space is advised to use the following files to read the device statistics.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 216)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 217) File /sys/block/zram<id>/stat
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 218)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 219) Represents block layer statistics. Read Documentation/block/stat.rst for
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 220) details.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 221)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 222) File /sys/block/zram<id>/io_stat
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 223)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 224) The stat file represents device's I/O statistics not accounted by block
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 225) layer and, thus, not available in zram<id>/stat file. It consists of a
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 226) single line of text and contains the following stats separated by
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 227) whitespace:
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 228)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 229) ============= =============================================================
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 230) failed_reads The number of failed reads
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 231) failed_writes The number of failed writes
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 232) invalid_io The number of non-page-size-aligned I/O requests
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 233) notify_free Depending on device usage scenario it may account
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 234)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 235) a) the number of pages freed because of swap slot free
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 236) notifications
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 237) b) the number of pages freed because of
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 238) REQ_OP_DISCARD requests sent by bio. The former ones are
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 239) sent to a swap block device when a swap slot is freed,
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 240) which implies that this disk is being used as a swap disk.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 241)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 242) The latter ones are sent by filesystem mounted with
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 243) discard option, whenever some data blocks are getting
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 244) discarded.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 245) ============= =============================================================
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 246)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 247) File /sys/block/zram<id>/mm_stat
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 248)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 249) The mm_stat file represents the device's mm statistics. It consists of a single
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 250) line of text and contains the following stats separated by whitespace:
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 251)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 252) ================ =============================================================
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 253) orig_data_size uncompressed size of data stored in this disk.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 254) Unit: bytes
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 255) compr_data_size compressed size of data stored in this disk
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 256) mem_used_total the amount of memory allocated for this disk. This
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 257) includes allocator fragmentation and metadata overhead,
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 258) allocated for this disk. So, allocator space efficiency
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 259) can be calculated using compr_data_size and this statistic.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 260) Unit: bytes
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 261) mem_limit the maximum amount of memory ZRAM can use to store
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 262) the compressed data
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 263) mem_used_max the maximum amount of memory zram has consumed to
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 264) store the data
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 265) same_pages the number of same element filled pages written to this disk.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 266) No memory is allocated for such pages.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 267) pages_compacted the number of pages freed during compaction
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 268) huge_pages the number of incompressible pages
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 269) ================ =============================================================
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 270)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 271) File /sys/block/zram<id>/bd_stat
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 272)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 273) The bd_stat file represents a device's backing device statistics. It consists of
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 274) a single line of text and contains the following stats separated by whitespace:
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 275)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 276) ============== =============================================================
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 277) bd_count size of data written in backing device.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 278) Unit: 4K bytes
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 279) bd_reads the number of reads from backing device
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 280) Unit: 4K bytes
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 281) bd_writes the number of writes to backing device
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 282) Unit: 4K bytes
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 283) ============== =============================================================
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 284)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 285) 9) Deactivate
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 286) =============
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 287)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 288) ::
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 289)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 290) swapoff /dev/zram0
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 291) umount /dev/zram1
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 292)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 293) 10) Reset
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 294) =========
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 295)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 296) Write any positive value to 'reset' sysfs node::
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 297)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 298) echo 1 > /sys/block/zram0/reset
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 299) echo 1 > /sys/block/zram1/reset
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 300)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 301) This frees all the memory allocated for the given device and
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 302) resets the disksize to zero. You must set the disksize again
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 303) before reusing the device.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 304)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 305) Optional Feature
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 306) ================
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 307)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 308) writeback
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 309) ---------
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 310)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 311) With CONFIG_ZRAM_WRITEBACK, zram can write idle/incompressible page
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 312) to backing storage rather than keeping it in memory.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 313) To use the feature, admin should set up backing device via::
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 314)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 315) echo /dev/sda5 > /sys/block/zramX/backing_dev
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 316)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 317) before disksize setting. It supports only partition at this moment.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 318) If admin wants to use incompressible page writeback, they could do via::
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 319)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 320) echo huge > /sys/block/zramX/writeback
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 321)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 322) To use idle page writeback, first, user need to declare zram pages
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 323) as idle::
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 324)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 325) echo all > /sys/block/zramX/idle
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 326)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 327) From now on, any pages on zram are idle pages. The idle mark
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 328) will be removed until someone requests access of the block.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 329) IOW, unless there is access request, those pages are still idle pages.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 330)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 331) Admin can request writeback of those idle pages at right timing via::
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 332)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 333) echo idle > /sys/block/zramX/writeback
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 334)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 335) With the command, zram writeback idle pages from memory to the storage.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 336)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 337) If admin want to write a specific page in zram device to backing device,
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 338) they could write a page index into the interface.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 339)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 340) echo "page_index=1251" > /sys/block/zramX/writeback
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 341)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 342) If there are lots of write IO with flash device, potentially, it has
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 343) flash wearout problem so that admin needs to design write limitation
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 344) to guarantee storage health for entire product life.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 345)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 346) To overcome the concern, zram supports "writeback_limit" feature.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 347) The "writeback_limit_enable"'s default value is 0 so that it doesn't limit
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 348) any writeback. IOW, if admin wants to apply writeback budget, he should
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 349) enable writeback_limit_enable via::
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 350)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 351) $ echo 1 > /sys/block/zramX/writeback_limit_enable
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 352)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 353) Once writeback_limit_enable is set, zram doesn't allow any writeback
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 354) until admin sets the budget via /sys/block/zramX/writeback_limit.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 355)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 356) (If admin doesn't enable writeback_limit_enable, writeback_limit's value
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 357) assigned via /sys/block/zramX/writeback_limit is meaningless.)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 358)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 359) If admin want to limit writeback as per-day 400M, he could do it
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 360) like below::
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 361)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 362) $ MB_SHIFT=20
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 363) $ 4K_SHIFT=12
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 364) $ echo $((400<<MB_SHIFT>>4K_SHIFT)) > \
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 365) /sys/block/zram0/writeback_limit.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 366) $ echo 1 > /sys/block/zram0/writeback_limit_enable
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 367)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 368) If admins want to allow further write again once the bugdet is exhausted,
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 369) he could do it like below::
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 370)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 371) $ echo $((400<<MB_SHIFT>>4K_SHIFT)) > \
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 372) /sys/block/zram0/writeback_limit
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 373)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 374) If admin wants to see remaining writeback budget since last set::
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 375)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 376) $ cat /sys/block/zramX/writeback_limit
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 377)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 378) If admin want to disable writeback limit, he could do::
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 379)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 380) $ echo 0 > /sys/block/zramX/writeback_limit_enable
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 381)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 382) The writeback_limit count will reset whenever you reset zram (e.g.,
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 383) system reboot, echo 1 > /sys/block/zramX/reset) so keeping how many of
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 384) writeback happened until you reset the zram to allocate extra writeback
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 385) budget in next setting is user's job.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 386)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 387) If admin wants to measure writeback count in a certain period, he could
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 388) know it via /sys/block/zram0/bd_stat's 3rd column.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 389)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 390) memory tracking
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 391) ===============
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 392)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 393) With CONFIG_ZRAM_MEMORY_TRACKING, user can know information of the
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 394) zram block. It could be useful to catch cold or incompressible
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 395) pages of the process with*pagemap.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 396)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 397) If you enable the feature, you could see block state via
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 398) /sys/kernel/debug/zram/zram0/block_state". The output is as follows::
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 399)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 400) 300 75.033841 .wh.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 401) 301 63.806904 s...
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 402) 302 63.806919 ..hi
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 403)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 404) First column
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 405) zram's block index.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 406) Second column
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 407) access time since the system was booted
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 408) Third column
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 409) state of the block:
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 410)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 411) s:
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 412) same page
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 413) w:
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 414) written page to backing store
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 415) h:
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 416) huge page
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 417) i:
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 418) idle page
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 419)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 420) First line of above example says 300th block is accessed at 75.033841sec
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 421) and the block's state is huge so it is written back to the backing
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 422) storage. It's a debugging feature so anyone shouldn't rely on it to work
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 423) properly.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 424)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 425) Nitin Gupta
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 426) ngupta@vflare.org
Orange Pi5 kernel
Deprecated Linux kernel 5.10.110 for OrangePi 5/5B/5+ boards
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