2010-08-10 01:26:56 +08:00
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What: /sys/block/zram<id>/disksize
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Date: August 2010
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Contact: Nitin Gupta <ngupta@vflare.org>
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Description:
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The disksize file is read-write and specifies the disk size
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which represents the limit on the *uncompressed* worth of data
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that can be stored in this disk.
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2013-08-27 05:55:44 +08:00
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Unit: bytes
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2010-08-10 01:26:56 +08:00
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What: /sys/block/zram<id>/initstate
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Date: August 2010
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Contact: Nitin Gupta <ngupta@vflare.org>
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Description:
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2013-08-27 05:55:44 +08:00
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The initstate file is read-only and shows the initialization
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2010-08-10 01:26:56 +08:00
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state of the device.
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What: /sys/block/zram<id>/reset
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Date: August 2010
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Contact: Nitin Gupta <ngupta@vflare.org>
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Description:
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2013-08-27 05:55:44 +08:00
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The reset file is write-only and allows resetting the
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device. The reset operation frees all the memory associated
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2010-08-10 01:26:56 +08:00
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with this device.
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What: /sys/block/zram<id>/num_reads
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Date: August 2010
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Contact: Nitin Gupta <ngupta@vflare.org>
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Description:
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The num_reads file is read-only and specifies the number of
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reads (failed or successful) done on this device.
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What: /sys/block/zram<id>/num_writes
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Date: August 2010
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Contact: Nitin Gupta <ngupta@vflare.org>
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Description:
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The num_writes file is read-only and specifies the number of
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writes (failed or successful) done on this device.
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What: /sys/block/zram<id>/invalid_io
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Date: August 2010
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Contact: Nitin Gupta <ngupta@vflare.org>
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Description:
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The invalid_io file is read-only and specifies the number of
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non-page-size-aligned I/O requests issued to this device.
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2014-04-08 06:38:08 +08:00
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What: /sys/block/zram<id>/failed_reads
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Date: February 2014
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Contact: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
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Description:
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The failed_reads file is read-only and specifies the number of
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failed reads happened on this device.
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What: /sys/block/zram<id>/failed_writes
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Date: February 2014
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Contact: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
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Description:
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The failed_writes file is read-only and specifies the number of
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failed writes happened on this device.
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zram: add multi stream functionality
Existing zram (zcomp) implementation has only one compression stream
(buffer and algorithm private part), so in order to prevent data
corruption only one write (compress operation) can use this compression
stream, forcing all concurrent write operations to wait for stream lock
to be released. This patch changes zcomp to keep a compression streams
list of user-defined size (via sysfs device attr). Each write operation
still exclusively holds compression stream, the difference is that we
can have N write operations (depending on size of streams list)
executing in parallel. See TEST section later in commit message for
performance data.
Introduce struct zcomp_strm_multi and a set of functions to manage
zcomp_strm stream access. zcomp_strm_multi has a list of idle
zcomp_strm structs, spinlock to protect idle list and wait queue, making
it possible to perform parallel compressions.
The following set of functions added:
- zcomp_strm_multi_find()/zcomp_strm_multi_release()
find and release a compression stream, implement required locking
- zcomp_strm_multi_create()/zcomp_strm_multi_destroy()
create and destroy zcomp_strm_multi
zcomp ->strm_find() and ->strm_release() callbacks are set during
initialisation to zcomp_strm_multi_find()/zcomp_strm_multi_release()
correspondingly.
Each time zcomp issues a zcomp_strm_multi_find() call, the following set
of operations performed:
- spin lock strm_lock
- if idle list is not empty, remove zcomp_strm from idle list, spin
unlock and return zcomp stream pointer to caller
- if idle list is empty, current adds itself to wait queue. it will be
awaken by zcomp_strm_multi_release() caller.
zcomp_strm_multi_release():
- spin lock strm_lock
- add zcomp stream to idle list
- spin unlock, wake up sleeper
Minchan Kim reported that spinlock-based locking scheme has demonstrated
a severe perfomance regression for single compression stream case,
comparing to mutex-based (see https://lkml.org/lkml/2014/2/18/16)
base spinlock mutex
==Initial write ==Initial write ==Initial write
records: 5 records: 5 records: 5
avg: 1642424.35 avg: 699610.40 avg: 1655583.71
std: 39890.95(2.43%) std: 232014.19(33.16%) std: 52293.96
max: 1690170.94 max: 1163473.45 max: 1697164.75
min: 1568669.52 min: 573429.88 min: 1553410.23
==Rewrite ==Rewrite ==Rewrite
records: 5 records: 5 records: 5
avg: 1611775.39 avg: 501406.64 avg: 1684419.11
std: 17144.58(1.06%) std: 15354.41(3.06%) std: 18367.42
max: 1641800.95 max: 531356.78 max: 1706445.84
min: 1593515.27 min: 488817.78 min: 1655335.73
When only one compression stream available, mutex with spin on owner
tends to perform much better than frequent wait_event()/wake_up(). This
is why single stream implemented as a special case with mutex locking.
Introduce and document zram device attribute max_comp_streams. This
attr shows and stores current zcomp's max number of zcomp streams
(max_strm). Extend zcomp's zcomp_create() with `max_strm' parameter.
`max_strm' limits the number of zcomp_strm structs in compression
backend's idle list (max_comp_streams).
max_comp_streams used during initialisation as follows:
-- passing to zcomp_create() max_strm equals to 1 will initialise zcomp
using single compression stream zcomp_strm_single (mutex-based locking).
-- passing to zcomp_create() max_strm greater than 1 will initialise zcomp
using multi compression stream zcomp_strm_multi (spinlock-based locking).
default max_comp_streams value is 1, meaning that zram with single stream
will be initialised.
Later patch will introduce configuration knob to change max_comp_streams
on already initialised and used zcomp.
TEST
iozone -t 3 -R -r 16K -s 60M -I +Z
test base 1 strm (mutex) 3 strm (spinlock)
-----------------------------------------------------------------------
Initial write 589286.78 583518.39 718011.05
Rewrite 604837.97 596776.38 1515125.72
Random write 584120.11 595714.58 1388850.25
Pwrite 535731.17 541117.38 739295.27
Fwrite 1418083.88 1478612.72 1484927.06
Usage example:
set max_comp_streams to 4
echo 4 > /sys/block/zram0/max_comp_streams
show current max_comp_streams (default value is 1).
cat /sys/block/zram0/max_comp_streams
Signed-off-by: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
Acked-by: Minchan Kim <minchan@kernel.org>
Cc: Jerome Marchand <jmarchan@redhat.com>
Cc: Nitin Gupta <ngupta@vflare.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2014-04-08 06:38:14 +08:00
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What: /sys/block/zram<id>/max_comp_streams
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Date: February 2014
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Contact: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
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Description:
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The max_comp_streams file is read-write and specifies the
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number of backend's zcomp_strm compression streams (number of
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concurrent compress operations).
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2014-04-08 06:38:17 +08:00
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What: /sys/block/zram<id>/comp_algorithm
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Date: February 2014
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Contact: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
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Description:
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The comp_algorithm file is read-write and lets to show
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available and selected compression algorithms, change
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compression algorithm selection.
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2010-08-10 01:26:56 +08:00
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What: /sys/block/zram<id>/notify_free
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Date: August 2010
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Contact: Nitin Gupta <ngupta@vflare.org>
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Description:
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2014-10-10 06:29:57 +08:00
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The notify_free file is read-only. Depending on device usage
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scenario it may account a) the number of pages freed because
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of swap slot free notifications or b) the number of pages freed
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because of REQ_DISCARD requests sent by bio. The former ones
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are sent to a swap block device when a swap slot is freed, which
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implies that this disk is being used as a swap disk. The latter
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ones are sent by filesystem mounted with discard option,
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whenever some data blocks are getting discarded.
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2010-08-10 01:26:56 +08:00
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What: /sys/block/zram<id>/zero_pages
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Date: August 2010
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Contact: Nitin Gupta <ngupta@vflare.org>
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Description:
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The zero_pages file is read-only and specifies number of zero
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filled pages written to this disk. No memory is allocated for
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such pages.
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What: /sys/block/zram<id>/orig_data_size
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Date: August 2010
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Contact: Nitin Gupta <ngupta@vflare.org>
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Description:
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The orig_data_size file is read-only and specifies uncompressed
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size of data stored in this disk. This excludes zero-filled
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pages (zero_pages) since no memory is allocated for them.
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Unit: bytes
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What: /sys/block/zram<id>/compr_data_size
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Date: August 2010
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Contact: Nitin Gupta <ngupta@vflare.org>
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Description:
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The compr_data_size file is read-only and specifies compressed
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size of data stored in this disk. So, compression ratio can be
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calculated using orig_data_size and this statistic.
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Unit: bytes
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What: /sys/block/zram<id>/mem_used_total
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Date: August 2010
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Contact: Nitin Gupta <ngupta@vflare.org>
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Description:
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The mem_used_total file is read-only and specifies the amount
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of memory, including allocator fragmentation and metadata
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overhead, allocated for this disk. So, allocator space
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efficiency can be calculated using compr_data_size and this
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statistic.
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2012-07-21 04:35:17 +08:00
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Unit: bytes
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2014-10-10 06:29:53 +08:00
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2014-10-10 06:29:55 +08:00
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What: /sys/block/zram<id>/mem_used_max
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Date: August 2014
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Contact: Minchan Kim <minchan@kernel.org>
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Description:
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The mem_used_max file is read/write and specifies the amount
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of maximum memory zram have consumed to store compressed data.
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For resetting the value, you should write "0". Otherwise,
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you could see -EINVAL.
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Unit: bytes
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2014-10-10 06:29:53 +08:00
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What: /sys/block/zram<id>/mem_limit
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Date: August 2014
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Contact: Minchan Kim <minchan@kernel.org>
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Description:
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The mem_limit file is read/write and specifies the maximum
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amount of memory ZRAM can use to store the compressed data. The
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limit could be changed in run time and "0" means disable the
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limit. No limit is the initial state. Unit: bytes
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