Documentation: zram: various fixes in zram.rst
Fix various items in zram.rst: - typos/spellos - punctuation - grammar - shell syntax - indentation - sysfs file names Signed-off-by: Randy Dunlap <rdunlap@infradead.org> Acked-by: Minchan Kim <minchan@kernel.org> Link: https://lore.kernel.org/r/77000e12-677a-62f6-9f78-343be5bd6630@infradead.org Signed-off-by: Jonathan Corbet <corbet@lwn.net>
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Randy Dunlap
Jonathan Corbet
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@ -1,15 +1,15 @@
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========================================
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zram: Compressed RAM based block devices
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zram: Compressed RAM-based block devices
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========================================
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Introduction
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============
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The zram module creates RAM based block devices named /dev/zram<id>
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The zram module creates RAM-based block devices named /dev/zram<id>
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(<id> = 0, 1, ...). Pages written to these disks are compressed and stored
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in memory itself. These disks allow very fast I/O and compression provides
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good amounts of memory savings. Some of the usecases include /tmp storage,
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use as swap disks, various caches under /var and maybe many more :)
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good amounts of memory savings. Some of the use cases include /tmp storage,
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use as swap disks, various caches under /var and maybe many more. :)
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Statistics for individual zram devices are exported through sysfs nodes at
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/sys/block/zram<id>/
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@ -43,17 +43,17 @@ The list of possible return codes:
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======== =============================================================
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-EBUSY an attempt to modify an attribute that cannot be changed once
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the device has been initialised. Please reset device first;
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the device has been initialised. Please reset device first.
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-ENOMEM zram was not able to allocate enough memory to fulfil your
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needs;
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needs.
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-EINVAL invalid input has been provided.
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======== =============================================================
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If you use 'echo', the returned value that is changed by 'echo' utility,
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If you use 'echo', the returned value is set by the 'echo' utility,
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and, in general case, something like::
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echo 3 > /sys/block/zram0/max_comp_streams
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if [ $? -ne 0 ];
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if [ $? -ne 0 ]; then
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handle_error
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fi
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@ -65,7 +65,8 @@ should suffice.
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::
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modprobe zram num_devices=4
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This creates 4 devices: /dev/zram{0,1,2,3}
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This creates 4 devices: /dev/zram{0,1,2,3}
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num_devices parameter is optional and tells zram how many devices should be
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pre-created. Default: 1.
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@ -73,12 +74,12 @@ pre-created. Default: 1.
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2) Set max number of compression streams
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========================================
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Regardless the value passed to this attribute, ZRAM will always
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allocate multiple compression streams - one per online CPUs - thus
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Regardless of the value passed to this attribute, ZRAM will always
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allocate multiple compression streams - one per online CPU - thus
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allowing several concurrent compression operations. The number of
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allocated compression streams goes down when some of the CPUs
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become offline. There is no single-compression-stream mode anymore,
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unless you are running a UP system or has only 1 CPU online.
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unless you are running a UP system or have only 1 CPU online.
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To find out how many streams are currently available::
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@ -89,7 +90,7 @@ To find out how many streams are currently available::
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Using comp_algorithm device attribute one can see available and
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currently selected (shown in square brackets) compression algorithms,
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change selected compression algorithm (once the device is initialised
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or change the selected compression algorithm (once the device is initialised
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there is no way to change compression algorithm).
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Examples::
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@ -167,9 +168,9 @@ Examples::
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zram provides a control interface, which enables dynamic (on-demand) device
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addition and removal.
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In order to add a new /dev/zramX device, perform read operation on hot_add
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attribute. This will return either new device's device id (meaning that you
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can use /dev/zram<id>) or error code.
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In order to add a new /dev/zramX device, perform a read operation on the hot_add
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attribute. This will return either the new device's device id (meaning that you
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can use /dev/zram<id>) or an error code.
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Example::
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@ -186,8 +187,8 @@ execute::
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Per-device statistics are exported as various nodes under /sys/block/zram<id>/
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A brief description of exported device attributes. For more details please
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read Documentation/ABI/testing/sysfs-block-zram.
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A brief description of exported device attributes follows. For more details
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please read Documentation/ABI/testing/sysfs-block-zram.
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====================== ====== ===============================================
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Name access description
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@ -245,7 +246,7 @@ whitespace:
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File /sys/block/zram<id>/mm_stat
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The stat file represents device's mm statistics. It consists of a single
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The mm_stat file represents the device's mm statistics. It consists of a single
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line of text and contains the following stats separated by whitespace:
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================ =============================================================
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@ -261,7 +262,7 @@ line of text and contains the following stats separated by whitespace:
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Unit: bytes
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mem_limit the maximum amount of memory ZRAM can use to store
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the compressed data
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mem_used_max the maximum amount of memory zram have consumed to
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mem_used_max the maximum amount of memory zram has consumed to
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store the data
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same_pages the number of same element filled pages written to this disk.
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No memory is allocated for such pages.
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@ -271,7 +272,7 @@ line of text and contains the following stats separated by whitespace:
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File /sys/block/zram<id>/bd_stat
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The stat file represents device's backing device statistics. It consists of
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The bd_stat file represents a device's backing device statistics. It consists of
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a single line of text and contains the following stats separated by whitespace:
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============== =============================================================
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@ -316,7 +317,7 @@ To use the feature, admin should set up backing device via::
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echo /dev/sda5 > /sys/block/zramX/backing_dev
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before disksize setting. It supports only partition at this moment.
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If admin want to use incompressible page writeback, they could do via::
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If admin wants to use incompressible page writeback, they could do via::
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echo huge > /sys/block/zramX/write
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@ -326,7 +327,7 @@ as idle::
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echo all > /sys/block/zramX/idle
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From now on, any pages on zram are idle pages. The idle mark
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will be removed until someone request access of the block.
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will be removed until someone requests access of the block.
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IOW, unless there is access request, those pages are still idle pages.
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Admin can request writeback of those idle pages at right timing via::
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@ -341,16 +342,16 @@ to guarantee storage health for entire product life.
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To overcome the concern, zram supports "writeback_limit" feature.
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The "writeback_limit_enable"'s default value is 0 so that it doesn't limit
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any writeback. IOW, if admin want to apply writeback budget, he should
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any writeback. IOW, if admin wants to apply writeback budget, he should
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enable writeback_limit_enable via::
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$ echo 1 > /sys/block/zramX/writeback_limit_enable
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Once writeback_limit_enable is set, zram doesn't allow any writeback
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until admin set the budget via /sys/block/zramX/writeback_limit.
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until admin sets the budget via /sys/block/zramX/writeback_limit.
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(If admin doesn't enable writeback_limit_enable, writeback_limit's value
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assigned via /sys/block/zramX/writeback_limit is meaninless.)
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assigned via /sys/block/zramX/writeback_limit is meaningless.)
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If admin want to limit writeback as per-day 400M, he could do it
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like below::
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@ -361,13 +362,13 @@ like below::
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/sys/block/zram0/writeback_limit.
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$ echo 1 > /sys/block/zram0/writeback_limit_enable
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If admin want to allow further write again once the bugdet is exausted,
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If admins want to allow further write again once the bugdet is exhausted,
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he could do it like below::
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$ echo $((400<<MB_SHIFT>>4K_SHIFT)) > \
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/sys/block/zram0/writeback_limit
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If admin want to see remaining writeback budget since he set::
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If admin wants to see remaining writeback budget since last set::
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$ cat /sys/block/zramX/writeback_limit
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@ -375,12 +376,12 @@ If admin want to disable writeback limit, he could do::
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$ echo 0 > /sys/block/zramX/writeback_limit_enable
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The writeback_limit count will reset whenever you reset zram(e.g.,
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The writeback_limit count will reset whenever you reset zram (e.g.,
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system reboot, echo 1 > /sys/block/zramX/reset) so keeping how many of
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writeback happened until you reset the zram to allocate extra writeback
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budget in next setting is user's job.
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If admin want to measure writeback count in a certain period, he could
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If admin wants to measure writeback count in a certain period, he could
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know it via /sys/block/zram0/bd_stat's 3rd column.
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memory tracking
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