diff options
Diffstat (limited to 'Documentation/admin-guide/blockdev')
| -rw-r--r-- | Documentation/admin-guide/blockdev/index.rst | 1 | ||||
| -rw-r--r-- | Documentation/admin-guide/blockdev/zoned_loop.rst | 169 | ||||
| -rw-r--r-- | Documentation/admin-guide/blockdev/zram.rst | 58 |
3 files changed, 208 insertions, 20 deletions
diff --git a/Documentation/admin-guide/blockdev/index.rst b/Documentation/admin-guide/blockdev/index.rst index 957ccf617797..3262397ebe8f 100644 --- a/Documentation/admin-guide/blockdev/index.rst +++ b/Documentation/admin-guide/blockdev/index.rst @@ -11,6 +11,7 @@ Block Devices nbd paride ramdisk + zoned_loop zram drbd/index diff --git a/Documentation/admin-guide/blockdev/zoned_loop.rst b/Documentation/admin-guide/blockdev/zoned_loop.rst new file mode 100644 index 000000000000..9c7aa3b482f3 --- /dev/null +++ b/Documentation/admin-guide/blockdev/zoned_loop.rst @@ -0,0 +1,169 @@ +.. SPDX-License-Identifier: GPL-2.0 + +======================= +Zoned Loop Block Device +======================= + +.. Contents: + + 1) Overview + 2) Creating a Zoned Device + 3) Deleting a Zoned Device + 4) Example + + +1) Overview +----------- + +The zoned loop block device driver (zloop) allows a user to create a zoned block +device using one regular file per zone as backing storage. This driver does not +directly control any hardware and uses read, write and truncate operations to +regular files of a file system to emulate a zoned block device. + +Using zloop, zoned block devices with a configurable capacity, zone size and +number of conventional zones can be created. The storage for each zone of the +device is implemented using a regular file with a maximum size equal to the zone +size. The size of a file backing a conventional zone is always equal to the zone +size. The size of a file backing a sequential zone indicates the amount of data +sequentially written to the file, that is, the size of the file directly +indicates the position of the write pointer of the zone. + +When resetting a sequential zone, its backing file size is truncated to zero. +Conversely, for a zone finish operation, the backing file is truncated to the +zone size. With this, the maximum capacity of a zloop zoned block device created +can be larger configured to be larger than the storage space available on the +backing file system. Of course, for such configuration, writing more data than +the storage space available on the backing file system will result in write +errors. + +The zoned loop block device driver implements a complete zone transition state +machine. That is, zones can be empty, implicitly opened, explicitly opened, +closed or full. The current implementation does not support any limits on the +maximum number of open and active zones. + +No user tools are necessary to create and delete zloop devices. + +2) Creating a Zoned Device +-------------------------- + +Once the zloop module is loaded (or if zloop is compiled in the kernel), the +character device file /dev/zloop-control can be used to add a zloop device. +This is done by writing an "add" command directly to the /dev/zloop-control +device:: + + $ modprobe zloop + $ ls -l /dev/zloop* + crw-------. 1 root root 10, 123 Jan 6 19:18 /dev/zloop-control + + $ mkdir -p <base directory/<device ID> + $ echo "add [options]" > /dev/zloop-control + +The options available for the add command can be listed by reading the +/dev/zloop-control device:: + + $ cat /dev/zloop-control + add id=%d,capacity_mb=%u,zone_size_mb=%u,zone_capacity_mb=%u,conv_zones=%u,base_dir=%s,nr_queues=%u,queue_depth=%u,buffered_io + remove id=%d + +In more details, the options that can be used with the "add" command are as +follows. + +================ =========================================================== +id Device number (the X in /dev/zloopX). + Default: automatically assigned. +capacity_mb Device total capacity in MiB. This is always rounded up to + the nearest higher multiple of the zone size. + Default: 16384 MiB (16 GiB). +zone_size_mb Device zone size in MiB. Default: 256 MiB. +zone_capacity_mb Device zone capacity (must always be equal to or lower than + the zone size. Default: zone size. +conv_zones Total number of conventioanl zones starting from sector 0. + Default: 8. +base_dir Path to the base directoy where to create the directory + containing the zone files of the device. + Default=/var/local/zloop. + The device directory containing the zone files is always + named with the device ID. E.g. the default zone file + directory for /dev/zloop0 is /var/local/zloop/0. +nr_queues Number of I/O queues of the zoned block device. This value is + always capped by the number of online CPUs + Default: 1 +queue_depth Maximum I/O queue depth per I/O queue. + Default: 64 +buffered_io Do buffered IOs instead of direct IOs (default: false) +================ =========================================================== + +3) Deleting a Zoned Device +-------------------------- + +Deleting an unused zoned loop block device is done by issuing the "remove" +command to /dev/zloop-control, specifying the ID of the device to remove:: + + $ echo "remove id=X" > /dev/zloop-control + +The remove command does not have any option. + +A zoned device that was removed can be re-added again without any change to the +state of the device zones: the device zones are restored to their last state +before the device was removed. Adding again a zoned device after it was removed +must always be done using the same configuration as when the device was first +added. If a zone configuration change is detected, an error will be returned and +the zoned device will not be created. + +To fully delete a zoned device, after executing the remove operation, the device +base directory containing the backing files of the device zones must be deleted. + +4) Example +---------- + +The following sequence of commands creates a 2GB zoned device with zones of 64 +MB and a zone capacity of 63 MB:: + + $ modprobe zloop + $ mkdir -p /var/local/zloop/0 + $ echo "add capacity_mb=2048,zone_size_mb=64,zone_capacity=63MB" > /dev/zloop-control + +For the device created (/dev/zloop0), the zone backing files are all created +under the default base directory (/var/local/zloop):: + + $ ls -l /var/local/zloop/0 + total 0 + -rw-------. 1 root root 67108864 Jan 6 22:23 cnv-000000 + -rw-------. 1 root root 67108864 Jan 6 22:23 cnv-000001 + -rw-------. 1 root root 67108864 Jan 6 22:23 cnv-000002 + -rw-------. 1 root root 67108864 Jan 6 22:23 cnv-000003 + -rw-------. 1 root root 67108864 Jan 6 22:23 cnv-000004 + -rw-------. 1 root root 67108864 Jan 6 22:23 cnv-000005 + -rw-------. 1 root root 67108864 Jan 6 22:23 cnv-000006 + -rw-------. 1 root root 67108864 Jan 6 22:23 cnv-000007 + -rw-------. 1 root root 0 Jan 6 22:23 seq-000008 + -rw-------. 1 root root 0 Jan 6 22:23 seq-000009 + ... + +The zoned device created (/dev/zloop0) can then be used normally:: + + $ lsblk -z + NAME ZONED ZONE-SZ ZONE-NR ZONE-AMAX ZONE-OMAX ZONE-APP ZONE-WGRAN + zloop0 host-managed 64M 32 0 0 1M 4K + $ blkzone report /dev/zloop0 + start: 0x000000000, len 0x020000, cap 0x020000, wptr 0x000000 reset:0 non-seq:0, zcond: 0(nw) [type: 1(CONVENTIONAL)] + start: 0x000020000, len 0x020000, cap 0x020000, wptr 0x000000 reset:0 non-seq:0, zcond: 0(nw) [type: 1(CONVENTIONAL)] + start: 0x000040000, len 0x020000, cap 0x020000, wptr 0x000000 reset:0 non-seq:0, zcond: 0(nw) [type: 1(CONVENTIONAL)] + start: 0x000060000, len 0x020000, cap 0x020000, wptr 0x000000 reset:0 non-seq:0, zcond: 0(nw) [type: 1(CONVENTIONAL)] + start: 0x000080000, len 0x020000, cap 0x020000, wptr 0x000000 reset:0 non-seq:0, zcond: 0(nw) [type: 1(CONVENTIONAL)] + start: 0x0000a0000, len 0x020000, cap 0x020000, wptr 0x000000 reset:0 non-seq:0, zcond: 0(nw) [type: 1(CONVENTIONAL)] + start: 0x0000c0000, len 0x020000, cap 0x020000, wptr 0x000000 reset:0 non-seq:0, zcond: 0(nw) [type: 1(CONVENTIONAL)] + start: 0x0000e0000, len 0x020000, cap 0x020000, wptr 0x000000 reset:0 non-seq:0, zcond: 0(nw) [type: 1(CONVENTIONAL)] + start: 0x000100000, len 0x020000, cap 0x01f800, wptr 0x000000 reset:0 non-seq:0, zcond: 1(em) [type: 2(SEQ_WRITE_REQUIRED)] + start: 0x000120000, len 0x020000, cap 0x01f800, wptr 0x000000 reset:0 non-seq:0, zcond: 1(em) [type: 2(SEQ_WRITE_REQUIRED)] + ... + +Deleting this device is done using the command:: + + $ echo "remove id=0" > /dev/zloop-control + +The removed device can be re-added again using the same "add" command as when +the device was first created. To fully delete a zoned device, its backing files +should also be deleted after executing the remove command:: + + $ rm -r /var/local/zloop/0 diff --git a/Documentation/admin-guide/blockdev/zram.rst b/Documentation/admin-guide/blockdev/zram.rst index 9bdb30901a93..3e273c1bb749 100644 --- a/Documentation/admin-guide/blockdev/zram.rst +++ b/Documentation/admin-guide/blockdev/zram.rst @@ -317,6 +317,26 @@ a single line of text and contains the following stats separated by whitespace: Optional Feature ================ +IDLE pages tracking +------------------- + +zram has built-in support for idle pages tracking (that is, allocated but +not used pages). This feature is useful for e.g. zram writeback and +recompression. In order to mark pages as idle, execute the following command:: + + echo all > /sys/block/zramX/idle + +This will mark all allocated zram pages as idle. The idle mark will be +removed only when the page (block) is accessed (e.g. overwritten or freed). +Additionally, when CONFIG_ZRAM_TRACK_ENTRY_ACTIME is enabled, pages can be +marked as idle based on how many seconds have passed since the last access to +a particular zram page:: + + echo 86400 > /sys/block/zramX/idle + +In this example, all pages which haven't been accessed in more than 86400 +seconds (one day) will be marked idle. + writeback --------- @@ -331,24 +351,7 @@ If admin wants to use incompressible page writeback, they could do it via:: echo huge > /sys/block/zramX/writeback -To use idle page writeback, first, user need to declare zram pages -as idle:: - - echo all > /sys/block/zramX/idle - -From now on, any pages on zram are idle pages. The idle mark -will be removed until someone requests access of the block. -IOW, unless there is access request, those pages are still idle pages. -Additionally, when CONFIG_ZRAM_TRACK_ENTRY_ACTIME is enabled pages can be -marked as idle based on how long (in seconds) it's been since they were -last accessed:: - - echo 86400 > /sys/block/zramX/idle - -In this example all pages which haven't been accessed in more than 86400 -seconds (one day) will be marked idle. - -Admin can request writeback of those idle pages at right timing via:: +Admin can request writeback of idle pages at right timing via:: echo idle > /sys/block/zramX/writeback @@ -369,6 +372,23 @@ they could write a page index into the interface:: echo "page_index=1251" > /sys/block/zramX/writeback +In Linux 6.16 this interface underwent some rework. First, the interface +now supports `key=value` format for all of its parameters (`type=huge_idle`, +etc.) Second, the support for `page_indexes` was introduced, which specify +`LOW-HIGH` range (or ranges) of pages to be written-back. This reduces the +number of syscalls, but more importantly this enables optimal post-processing +target selection strategy. Usage example:: + + echo "type=idle" > /sys/block/zramX/writeback + echo "page_indexes=1-100 page_indexes=200-300" > \ + /sys/block/zramX/writeback + +We also now permit multiple page_index params per call and a mix of +single pages and page ranges:: + + echo page_index=42 page_index=99 page_indexes=100-200 \ + page_indexes=500-700 > /sys/block/zramX/writeback + If there are lots of write IO with flash device, potentially, it has flash wearout problem so that admin needs to design write limitation to guarantee storage health for entire product life. @@ -482,8 +502,6 @@ attempt to recompress::: echo "type=huge_idle max_pages=42" > /sys/block/zramX/recompress -Recompression of idle pages requires memory tracking. - During re-compression for every page, that matches re-compression criteria, ZRAM iterates the list of registered alternative compression algorithms in order of their priorities. ZRAM stops either when re-compression was |