zram: remove max_comp_streams device attr

max_comp_streams device attribute has been defunct since May 2016 when
zram switched to per-CPU compression streams, remove it.

Link: https://lkml.kernel.o

zram: remove max_comp_streams device attr

max_comp_streams device attribute has been defunct since May 2016 when
zram switched to per-CPU compression streams, remove it.

Link: https://lkml.kernel.org/r/[email protected]
Signed-off-by: Sergey Senozhatsky <[email protected]>
Cc: Hillf Danton <[email protected]>
Cc: Kairui Song <[email protected]>
Cc: Minchan Kim <[email protected]>
Cc: Sebastian Andrzej Siewior <[email protected]>
Cc: Yosry Ahmed <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>

show more ...

zram: introduce algorithm_params device attribute

This attribute is used to setup compression algorithms' parameters, so we
can tweak algorithms' characteristics. At this point only 'level' is
supp

zram: introduce algorithm_params device attribute

This attribute is used to setup compression algorithms' parameters, so we
can tweak algorithms' characteristics. At this point only 'level' is
supported (to be extended in the future).

Each call sets up parameters for one particular algorithm, which should be
specified either by the algorithm's priority or algo name. This is
expected to be called after corresponding algorithm is selected via
comp_algorithm or recomp_algorithm.

echo "priority=0 level=1" > /sys/block/zram0/algorithm_params
or
echo "algo=zstd level=1" > /sys/block/zram0/algorithm_params

Link: https://lkml.kernel.org/r/[email protected]
Signed-off-by: Sergey Senozhatsky <[email protected]>
Cc: Minchan Kim <[email protected]>
Cc: Nick Terrell <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>

show more ...

Docs/ABI/zram: document zram recompress sysfs knobs

Document zram re-compression sysfs knobs.

Link: https://lkml.kernel.org/r/[email protected]
Signed-off-by: Sergey

Docs/ABI/zram: document zram recompress sysfs knobs

Document zram re-compression sysfs knobs.

Link: https://lkml.kernel.org/r/[email protected]
Signed-off-by: Sergey Senozhatsky <[email protected]>
Acked-by: Minchan Kim <[email protected]>
Cc: Nitin Gupta <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>

show more ...

zram: idle writeback fixes and cleanup

This patch includes some fixes and cleanup for idle-page writeback.

1. writeback_limit interface

Now writeback_limit interface is rather conusing. For examp

zram: idle writeback fixes and cleanup

This patch includes some fixes and cleanup for idle-page writeback.

1. writeback_limit interface

Now writeback_limit interface is rather conusing. For example, once
writeback limit budget is exausted, admin can see 0 from
/sys/block/zramX/writeback_limit which is same semantic with disable
writeback_limit at this moment. IOW, admin cannot tell that zero came
from disable writeback limit or exausted writeback limit.

To make the interface clear, let's sepatate enable of writeback limit to
another knob - /sys/block/zram0/writeback_limit_enable

* before:
while true :
# to re-enable writeback limit once previous one is used up
echo 0 > /sys/block/zram0/writeback_limit
echo $((200<<20)) > /sys/block/zram0/writeback_limit
..
.. # used up the writeback limit budget

* new
# To enable writeback limit, from the beginning, admin should
# enable it.
echo $((200<<20)) > /sys/block/zram0/writeback_limit
echo 1 > /sys/block/zram/0/writeback_limit_enable
while true :
echo $((200<<20)) > /sys/block/zram0/writeback_limit
..
.. # used up the writeback limit budget

It's much strightforward.

2. fix condition check idle/huge writeback mode check

The mode in writeback_store is not bit opeartion any more so no need to
use bit operations. Furthermore, current condition check is broken in
that it does writeback every pages regardless of huge/idle.

3. clean up idle_store

No need to use goto.

[[email protected]: missed spin_lock_init]
Link: http://lkml.kernel.org/r/[email protected]
Link: http://lkml.kernel.org/r/[email protected]
Signed-off-by: Minchan Kim <[email protected]>
Suggested-by: John Dias <[email protected]>
Cc: Sergey Senozhatsky <[email protected]>
Cc: John Dias <[email protected]>
Cc: Srinivas Paladugu <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>

show more ...

zram: writeback throttle

If there are lots of write IO with flash device, it could have a
wearout problem of storage. To overcome the problem, admin needs
to design write limitation to guarantee fla

zram: writeback throttle

If there are lots of write IO with flash device, it could have a
wearout problem of storage. To overcome the problem, admin needs
to design write limitation to guarantee flash health
for entire product life.

This patch creates a new knob "writeback_limit" for zram.

writeback_limit's default value is 0 so that it doesn't limit
any writeback. If admin want to measure writeback count in a
certain period, he could know it via /sys/block/zram0/bd_stat's
3rd column.

If admin want to limit writeback as per-day 400M, he could do it
like below.

MB_SHIFT=20
4K_SHIFT=12
echo $((400<<MB_SHIFT>>4K_SHIFT)) > \
/sys/block/zram0/writeback_limit.

If admin want to allow further write again, he could do it like below

echo 0 > /sys/block/zram0/writeback_limit

If admin want to see remaining writeback budget,

cat /sys/block/zram0/writeback_limit

The writeback_limit count will reset whenever you reset zram (e.g., system
reboot, echo 1 > /sys/block/zramX/reset) so keeping how many of writeback
happened until you reset the zram to allocate extra writeback budget in
next setting is user's job.

[[email protected]: v4]
Link: http://lkml.kernel.org/r/[email protected]
Link: http://lkml.kernel.org/r/[email protected]
Signed-off-by: Minchan Kim <[email protected]>
Reviewed-by: Sergey Senozhatsky <[email protected]>
Cc: Joey Pabalinas <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>

show more ...

zram: add bd_stat statistics

bd_stat represents things that happened in the backing device. Currently
it supports bd_counts, bd_reads and bd_writes which are helpful to
understand wearout of flash

zram: add bd_stat statistics

bd_stat represents things that happened in the backing device. Currently
it supports bd_counts, bd_reads and bd_writes which are helpful to
understand wearout of flash and memory saving.

[[email protected]: v4]
Link: http://lkml.kernel.org/r/[email protected]
Link: http://lkml.kernel.org/r/[email protected]
Signed-off-by: Minchan Kim <[email protected]>
Reviewed-by: Sergey Senozhatsky <[email protected]>
Cc: Joey Pabalinas <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>

show more ...

zram: support idle/huge page writeback

Add a new feature "zram idle/huge page writeback". In the zram-swap use
case, zram usually has many idle/huge swap pages. It's pointless to keep
them in memo

zram: support idle/huge page writeback

Add a new feature "zram idle/huge page writeback". In the zram-swap use
case, zram usually has many idle/huge swap pages. It's pointless to keep
them in memory (ie, zram).

To solve this problem, this feature introduces idle/huge page writeback to
the backing device so the goal is to save more memory space on embedded
systems.

Normal sequence to use idle/huge page writeback feature is as follows,

while (1) {
# mark allocated zram slot to idle
echo all > /sys/block/zram0/idle
# leave system working for several hours
# Unless there is no access for some blocks on zram,
# they are still IDLE marked pages.

echo "idle" > /sys/block/zram0/writeback
or/and
echo "huge" > /sys/block/zram0/writeback
# write the IDLE or/and huge marked slot into backing device
# and free the memory.
}

Per the discussion at
https://lore.kernel.org/lkml/20181122065926.GG3441@jagdpanzerIV/T/#u,

This patch removes direct incommpressibe page writeback feature
(d2afd25114f4 ("zram: write incompressible pages to backing device")).

Below concerns from Sergey:
== &< ==

"IDLE writeback" is superior to "incompressible writeback".

"incompressible writeback" is completely unpredictable and uncontrollable;
it depens on data patterns and compression algorithms. While "IDLE
writeback" is predictable.

I even suspect, that, *ideally*, we can remove "incompressible writeback".
"IDLE pages" is a super set which also includes "incompressible" pages.
So, technically, we still can do "incompressible writeback" from "IDLE
writeback" path; but a much more reasonable one, based on a page idling
period.

I understand that you want to keep "direct incompressible writeback"
around. ZRAM is especially popular on devices which do suffer from flash
wearout, so I can see "incompressible writeback" path becoming a dead
code, long term.

== &< ==

Below concerns from Minchan:
== &< ==

My concern is if we enable CONFIG_ZRAM_WRITEBACK in this implementation,
both hugepage/idlepage writeck will turn on. However someuser want to
enable only idlepage writeback so we need to introduce turn on/off knob
for hugepage or new CONFIG_ZRAM_IDLEPAGE_WRITEBACK for those usecase. I
don't want to make it complicated *if possible*.

Long term, I imagine we need to make VM aware of new swap hierarchy a
little bit different with as-is. For example, first high priority swap
can return -EIO or -ENOCOMP, swap try to fallback to next lower priority
swap device. With that, hugepage writeback will work tranparently.

So we could regard it as regression because incompressible pages doesn't
go to backing storage automatically. Instead, user should do it via "echo
huge" > /sys/block/zram/writeback" manually.

== &< ==

Link: http://lkml.kernel.org/r/[email protected]
Signed-off-by: Minchan Kim <[email protected]>
Reviewed-by: Joey Pabalinas <[email protected]>
Reviewed-by: Sergey Senozhatsky <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>

show more ...

zram: introduce ZRAM_IDLE flag

To support idle page writeback with upcoming patches, this patch
introduces a new ZRAM_IDLE flag.

Userspace can mark zram slots as "idle" via
"echo all > /sys/block/

zram: introduce ZRAM_IDLE flag

To support idle page writeback with upcoming patches, this patch
introduces a new ZRAM_IDLE flag.

Userspace can mark zram slots as "idle" via
"echo all > /sys/block/zramX/idle"
which marks every allocated zram slot as ZRAM_IDLE.
User could see it by /sys/kernel/debug/zram/zram0/block_state.

300 75.033841 ...i
301 63.806904 s..i
302 63.806919 ..hi

Once there is IO for the slot, the mark will be disappeared.

300 75.033841 ...
301 63.806904 s..i
302 63.806919 ..hi

Therefore, 300th block is idle zpage. With this feature,
user can how many zram has idle pages which are waste of memory.

Link: http://lkml.kernel.org/r/[email protected]
Signed-off-by: Minchan Kim <[email protected]>
Reviewed-by: Sergey Senozhatsky <[email protected]>
Reviewed-by: Joey Pabalinas <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>

show more ...

zram: add config and doc file for writeback feature

This patch adds document and kconfig for using of writeback feature.

Link: http://lkml.kernel.org/r/1498459987-24562-10-git-send-email-minchan@ke

zram: add config and doc file for writeback feature

This patch adds document and kconfig for using of writeback feature.

Link: http://lkml.kernel.org/r/[email protected]
Signed-off-by: Minchan Kim <[email protected]>
Cc: Juneho Choi <[email protected]>
Cc: Sergey Senozhatsky <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>

show more ...

zram: remove obsolete sysfs attrs

We had a deprecated_attr_warn() warning for 2 years and now the time has
come and we finally can do the cleanup.

The plan was as follows:

: per-stat sysfs attribu

zram: remove obsolete sysfs attrs

We had a deprecated_attr_warn() warning for 2 years and now the time has
come and we finally can do the cleanup.

The plan was as follows:

: per-stat sysfs attributes are considered to be deprecated.
: The basic strategy is:
: -- the existing RW nodes will be downgraded to WO nodes (in linux 4.11)
: -- deprecated RO sysfs nodes will eventually be removed (in linux 4.11)
:
: The list of deprecated attributes can be found here:
: Documentation/ABI/obsolete/sysfs-block-zram
:
: Basically, every attribute that has its own read accessible sysfs
: node (e.g. num_reads) *AND* is accessible via one of the stat files
: (zram<id>/stat or zram<id>/io_stat or zram<id>/mm_stat) is considered
: to be deprecated.

The patch also removes `obsolete/sysfs-block-zram', clean ups
`testing/sysfs-block-zram' and tweaks zram.txt files.

Link: http://lkml.kernel.org/r/[email protected]
Signed-off-by: Sergey Senozhatsky <[email protected]>
Acked-by: Minchan Kim <[email protected]>
Cc: Jonathan Corbet <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>

show more ...

zram: introduce per-device debug_stat sysfs node

debug_stat sysfs is read-only and represents various debugging data that
zram developers may need. This file is not meant to be used by anyone
else:

zram: introduce per-device debug_stat sysfs node

debug_stat sysfs is read-only and represents various debugging data that
zram developers may need. This file is not meant to be used by anyone
else: its content is not documented and will change any time w/o any
notice. Therefore, the output of debug_stat file contains a version
string. To avoid any confusion, we will increase the version number
every time we modify the output.

At the moment this file exports only one value -- the number of
re-compressions, IOW, the number of times compression fast path has
failed. This stat is temporary any will be useful in case if any
per-cpu compression streams regressions will be reported.

Link: http://lkml.kernel.org/r/20160513230834.GB26763@bbox
Link: http://lkml.kernel.org/r/[email protected]
Signed-off-by: Sergey Senozhatsky <[email protected]>
Signed-off-by: Minchan Kim <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>

show more ...

zram: export new 'mm_stat' sysfs attrs

Per-device `zram<id>/mm_stat' file provides mm statistics of a particular
zram device in a format similar to block layer statistics. The file
consists of a si

zram: export new 'mm_stat' sysfs attrs

Per-device `zram<id>/mm_stat' file provides mm statistics of a particular
zram device in a format similar to block layer statistics. The file
consists of a single line and represents the following stats (separated by
whitespace):

orig_data_size
compr_data_size
mem_used_total
mem_limit
mem_used_max
zero_pages
num_migrated

Signed-off-by: Sergey Senozhatsky <[email protected]>
Acked-by: Minchan Kim <[email protected]>
Cc: Nitin Gupta <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>

show more ...

zram: export new 'io_stat' sysfs attrs

Per-device `zram<id>/io_stat' file provides accumulated I/O statistics of
particular zram device in a format similar to block layer statistics. The
file consi

zram: export new 'io_stat' sysfs attrs

Per-device `zram<id>/io_stat' file provides accumulated I/O statistics of
particular zram device in a format similar to block layer statistics. The
file consists of a single line and represents the following stats
(separated by whitespace):

failed_reads
failed_writes
invalid_io
notify_free

Signed-off-by: Sergey Senozhatsky <[email protected]>
Acked-by: Minchan Kim <[email protected]>
Cc: Nitin Gupta <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>

show more ...

zram: remove `num_migrated' device attr

This patch introduces rework to zram stats. We have per-stat sysfs nodes,
and it makes things a bit hard to use in user space: it doesn't give an
immediate s

zram: remove `num_migrated' device attr

This patch introduces rework to zram stats. We have per-stat sysfs nodes,
and it makes things a bit hard to use in user space: it doesn't give an
immediate stats 'snapshot', it requires user space to use more syscalls -
open, read, close for every stat file, with appropriate error checks on
every step, etc.

First, zram now accounts block layer statistics, available in
/sys/block/zram<id>/stat and /proc/diskstats files. So some new stats are
available (see Documentation/block/stat.txt), besides, zram's activities
now can be monitored by sysstat's iostat or similar tools.

Example:
cat /sys/block/zram0/stat
248 0 1984 0 251029 0 2008232 5120 0 5116 5116

Second, group currently exported on per-stat basis nodes into two
categories (files):

-- zram<id>/io_stat
accumulates device's IO stats, that are not accounted by block layer,
and contains:
failed_reads
failed_writes
invalid_io
notify_free

Example:
cat /sys/block/zram0/io_stat
0 0 0 652572

-- zram<id>/mm_stat
accumulates zram mm stats and contains:
orig_data_size
compr_data_size
mem_used_total
mem_limit
mem_used_max
zero_pages
num_migrated

Example:
cat /sys/block/zram0/mm_stat
434634752 270288572 279158784 0 579895296 15060 0

per-stat sysfs nodes are now considered to be deprecated and we plan to
remove them (and clean up some of the existing stat code) in two years (as
of now, there is no warning printed to syslog about deprecated stats being
used). User space is advised to use the above mentioned 3 files.

This patch (of 7):

Remove sysfs `num_migrated' attribute. We are moving away from per-stat
device attrs towards 3 stat files that will accumulate io and mm stats in
a format similar to block layer statistics in /sys/block/<dev>/stat. That
will be easier to use in user space, and reduce the number of syscalls
needed to read zram device statistics.

`num_migrated' will return back in zram<id>/mm_stat file.

Signed-off-by: Sergey Senozhatsky <[email protected]>
Acked-by: Minchan Kim <[email protected]>
Cc: Nitin Gupta <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>

show more ...

zram: support compaction

Now that zsmalloc supports compaction, zram can use it. For the first
step, this patch exports compact knob via sysfs so user can do compaction
via "echo 1 > /sys/block/zra

zram: support compaction

Now that zsmalloc supports compaction, zram can use it. For the first
step, this patch exports compact knob via sysfs so user can do compaction
via "echo 1 > /sys/block/zram0/compact".

Signed-off-by: Minchan Kim <[email protected]>
Cc: Juneho Choi <[email protected]>
Cc: Gunho Lee <[email protected]>
Cc: Luigi Semenzato <[email protected]>
Cc: Dan Streetman <[email protected]>
Cc: Seth Jennings <[email protected]>
Cc: Nitin Gupta <[email protected]>
Cc: Jerome Marchand <[email protected]>
Cc: Sergey Senozhatsky <[email protected]>
Cc: Joonsoo Kim <[email protected]>
Cc: Mel Gorman <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>

show more ...

zram: use notify_free to account all free notifications

`notify_free' device attribute accounts the number of slot free
notifications and internally represents the number of zram_free_page()
calls.

zram: use notify_free to account all free notifications

`notify_free' device attribute accounts the number of slot free
notifications and internally represents the number of zram_free_page()
calls. Slot free notifications are sent only when device is used as a
swap device, hence `notify_free' is used only for swap devices. Since
f4659d8e620d08 (zram: support REQ_DISCARD) ZRAM handles yet another one
free notification (also via zram_free_page() call) -- REQ_DISCARD
requests, which are sent by a filesystem, whenever some data blocks are
discarded. However, there is no way to know the number of notifications
in the latter case.

Use `notify_free' to account the number of pages freed by
zram_bio_discard() and zram_slot_free_notify(). Depending on usage
scenario `notify_free' represents:

a) the number of pages freed because of slot free notifications, which is
equal to the number of swap_slot_free_notify() calls, so there is no
behaviour change

b) the number of pages freed because of REQ_DISCARD notifications

Signed-off-by: Sergey Senozhatsky <[email protected]>
Acked-by: Minchan Kim <[email protected]>
Acked-by: Jerome Marchand <[email protected]>
Cc: Nitin Gupta <[email protected]>
Cc: Chao Yu <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>

show more ...

zram: report maximum used memory

Normally, zram user could get maximum memory usage zram consumed via
polling mem_used_total with sysfs in userspace.

But it has a critical problem because user can

zram: report maximum used memory

Normally, zram user could get maximum memory usage zram consumed via
polling mem_used_total with sysfs in userspace.

But it has a critical problem because user can miss peak memory usage
during update inverval of polling. For avoiding that, user should poll it
with shorter interval(ie, 0.0000000001s) with mlocking to avoid page fault
delay when memory pressure is heavy. It would be troublesome.

This patch adds new knob "mem_used_max" so user could see the maximum
memory usage easily via reading the knob and reset it via "echo 0 >
/sys/block/zram0/mem_used_max".

Signed-off-by: Minchan Kim <[email protected]>
Reviewed-by: Dan Streetman <[email protected]>
Cc: Sergey Senozhatsky <[email protected]>
Cc: Jerome Marchand <[email protected]>
Cc: <[email protected]>
Cc: <[email protected]>
Cc: Luigi Semenzato <[email protected]>
Cc: Nitin Gupta <[email protected]>
Cc: Seth Jennings <[email protected]>
Reviewed-by: David Horner <[email protected]>
Cc: Joonsoo Kim <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>

show more ...

zram: zram memory size limitation

Since zram has no control feature to limit memory usage, it makes hard to
manage system memrory.

This patch adds new knob "mem_limit" via sysfs to set up the a lim

zram: zram memory size limitation

Since zram has no control feature to limit memory usage, it makes hard to
manage system memrory.

This patch adds new knob "mem_limit" via sysfs to set up the a limit so
that zram could fail allocation once it reaches the limit.

In addition, user could change the limit in runtime so that he could
manage the memory more dynamically.

Initial state is no limit so it doesn't break old behavior.

[[email protected]: fix typo, per Sergey]
Signed-off-by: Minchan Kim <[email protected]>
Cc: Dan Streetman <[email protected]>
Cc: Sergey Senozhatsky <[email protected]>
Cc: Jerome Marchand <[email protected]>
Cc: <[email protected]>
Cc: <[email protected]>
Cc: Luigi Semenzato <[email protected]>
Cc: Nitin Gupta <[email protected]>
Cc: Seth Jennings <[email protected]>
Cc: David Horner <[email protected]>
Cc: Joonsoo Kim <[email protected]>
Cc: Minchan Kim <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>

show more ...

zram: make compression algorithm selection possible

Add and document `comp_algorithm' device attribute. This attribute allows
to show supported compression and currently selected compression
algori

zram: make compression algorithm selection possible

Add and document `comp_algorithm' device attribute. This attribute allows
to show supported compression and currently selected compression
algorithms:

cat /sys/block/zram0/comp_algorithm
[lzo] lz4

and change selected compression algorithm:
echo lzo > /sys/block/zram0/comp_algorithm

Signed-off-by: Sergey Senozhatsky <[email protected]>
Acked-by: Minchan Kim <[email protected]>
Cc: Jerome Marchand <[email protected]>
Cc: Nitin Gupta <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>

show more ...

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 (

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 <[email protected]>
Acked-by: Minchan Kim <[email protected]>
Cc: Jerome Marchand <[email protected]>
Cc: Nitin Gupta <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>

show more ...

zram: document failed_reads, failed_writes stats

Document `failed_reads' and `failed_writes' device attributes.
Remove info about `discard' - there is no such zram attr.

Signed-off-by: Sergey Senoz

zram: document failed_reads, failed_writes stats

Document `failed_reads' and `failed_writes' device attributes.
Remove info about `discard' - there is no such zram attr.

Signed-off-by: Sergey Senozhatsky <[email protected]>
Cc: Minchan Kim <[email protected]>
Cc: Jerome Marchand <[email protected]>
Cc: Nitin Gupta <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>

show more ...

zram: doc fixes

Simple doc updates to zram documentation.

Signed-off-by: Bernhard M. Wiedemann <[email protected]>
Acked-by: Rob Landley <[email protected]>
Signed-off-by: Jiri Kosina <jkosina@suse.

zram: doc fixes

Simple doc updates to zram documentation.

Signed-off-by: Bernhard M. Wiedemann <[email protected]>
Acked-by: Rob Landley <[email protected]>
Signed-off-by: Jiri Kosina <[email protected]>

show more ...

[media] Documentation: Add newline at end-of-file to files lacking one

This patch simply adds a newline character at end-of-file to those
files in Documentation/ that currently lack one.

This is do

[media] Documentation: Add newline at end-of-file to files lacking one

This patch simply adds a newline character at end-of-file to those
files in Documentation/ that currently lack one.

This is done for a few different reasons:

A) It's rather annoying when you do "cat some_file.txt" that your
prompt/cursor ends up at the end of the last line of output rather
than on a new line.

B) Some tools that process files line-by-line may get confused by the
lack of a newline on the last line.

C) The "\ No newline at end of file" line in diffs annoys me for some
reason.

So, let's just add the missing newline once and for all.

Signed-off-by: Jesper Juhl <[email protected]>
Signed-off-by: Mauro Carvalho Chehab <[email protected]>

show more ...

Documentation: Add newline at end-of-file to files lacking one

This patch simply adds a newline character at end-of-file to those
files in Documentation/ that currently lack one.

This is done for a

Documentation: Add newline at end-of-file to files lacking one

This patch simply adds a newline character at end-of-file to those
files in Documentation/ that currently lack one.

This is done for a few different reasons:

A) It's rather annoying when you do "cat some_file.txt" that your
prompt/cursor ends up at the end of the last line of output rather
than on a new line.

B) Some tools that process files line-by-line may get confused by the
lack of a newline on the last line.

C) The "\ No newline at end of file" line in diffs annoys me for some
reason.

So, let's just add the missing newline once and for all.

Signed-off-by: Jesper Juhl <[email protected]>
Signed-off-by: Jiri Kosina <[email protected]>

show more ...

Staging: zram: Document sysfs entries

Signed-off-by: Nitin Gupta <[email protected]>
Acked-by: Pekka Enberg <[email protected]>
Signed-off-by: Greg Kroah-Hartman <[email protected]>