zram: do not allocate physically contiguous strm buffers

Currently zram allocates 2 physically contiguous pages per-CPU's
compression stream (we may have up to 4 streams per-CPU). Since those
buffers are per-CPU we allocate them from CPU hotplug path, which may have
higher risks of failed allocations on devices with fragmented memory.

Switch to virtually contiguous allocations - crypto comp does not seem
impose requirements on compression working buffers to be physically
contiguous.

Link: https://lkml.kernel.org/r/20240213065400.6561-1-21cnbao@gmail.com
Signed-off-by: Barry Song <v-songbaohua@oppo.com>
Reviewed-by: Sergey Senozhatsky <senozhatsky@chromium.org>
Cc: Jens Axboe <axboe@kernel.dk>
Cc: Minchan Kim <minchan@kernel.org>
Cc: Sergey Senozhatsky <senozhatsky@chromium.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

zram: preparation for multi-zcomp support

Patch series "zram: Support multiple compression streams", v5.

This series adds support for multiple compression streams. The main idea
is that different compression algorithms have different characteristics
and zram may benefit when it uses a combination of algorithms: a default
algorithm that is faster but have lower compression rate and a secondary
algorithm that can use higher compression rate at a price of slower
compression/decompression.

There are several use-case for this functionality:

- huge pages re-compression: zstd or deflate can successfully compress
huge pages (~50% of huge pages on my synthetic ChromeOS tests), IOW
pages that lzo was not able to compress.

- idle pages re-compression: idle/cold pages sit in the memory and we
may reduce zsmalloc memory usage if we recompress those idle pages.

Userspace has a number of ways to control the behavior and impact of zram
recompression: what type of pages should be recompressed, size watermarks,
etc. Please refer to documentation patch.


This patch (of 13):

The patch turns compression streams and compressor algorithm name struct
zram members into arrays, so that we can have multiple compression streams
support (in the next patches).

The patch uses a rather explicit API for compressor selection:

- Get primary (default) compression stream
zcomp_stream_get(zram->comps[ZRAM_PRIMARY_COMP])
- Get secondary compression stream
zcomp_stream_get(zram->comps[ZRAM_SECONDARY_COMP])

We use similar API for compression streams put().

At this point we always have just one compression stream,
since CONFIG_ZRAM_MULTI_COMP is not yet defined.

Link: https://lkml.kernel.org/r/20221109115047.2921851-1-senozhatsky@chromium.org
Link: https://lkml.kernel.org/r/20221109115047.2921851-2-senozhatsky@chromium.org
Signed-off-by: Sergey Senozhatsky <senozhatsky@chromium.org>
Acked-by: Minchan Kim <minchan@kernel.org>
Cc: Minchan Kim <minchan@kernel.org>
Cc: Nitin Gupta <ngupta@vflare.org>
Cc: Suleiman Souhlal <suleiman@google.com>
Cc: Nhat Pham <nphamcs@gmail.com>
Cc: Alexey Romanov <avromanov@sberdevices.ru>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

zram: do not lookup algorithm in backends table

Always use crypto_has_comp() so that crypto can lookup module, call
usermodhelper to load the modules, wait for usermodhelper to finish and so
on. Otherwise crypto will do all of these steps under CPU hot-plug lock
and this looks like too much stuff to handle under the CPU hot-plug lock.
Besides this can end up in a deadlock when usermodhelper triggers a code
path that attempts to lock the CPU hot-plug lock, that zram already holds.

An example of such deadlock:

- path A. zram grabs CPU hot-plug lock, execs /sbin/modprobe from crypto
and waits for modprobe to finish

disksize_store
zcomp_create
__cpuhp_state_add_instance
__cpuhp_state_add_instance_cpuslocked
zcomp_cpu_up_prepare
crypto_alloc_base
crypto_alg_mod_lookup
call_usermodehelper_exec
wait_for_completion_killable
do_wait_for_common
schedule

- path B. async work kthread that brings in scsi device. It wants to
register CPUHP states at some point, and it needs the CPU hot-plug
lock for that, which is owned by zram.

async_run_entry_fn
scsi_probe_and_add_lun
scsi_mq_alloc_queue
blk_mq_init_queue
blk_mq_init_allocated_queue
blk_mq_realloc_hw_ctxs
__cpuhp_state_add_instance
__cpuhp_state_add_instance_cpuslocked
mutex_lock
schedule

- path C. modprobe sleeps, waiting for all aync works to finish.

load_module
do_init_module
async_synchronize_full
async_synchronize_cookie_domain
schedule

[senozhatsky@chromium.org: add comment]
Link: https://lkml.kernel.org/r/20220624060606.1014474-1-senozhatsky@chromium.org
Link: https://lkml.kernel.org/r/20220622023501.517125-1-senozhatsky@chromium.org
Signed-off-by: Sergey Senozhatsky <senozhatsky@chromium.org>
Cc: Minchan Kim <minchan@kernel.org>
Cc: Nitin Gupta <ngupta@vflare.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

zram: break the strict dependency from lzo

From the beginning, the zram block device always enabled CRYPTO_LZO,
since lzo-rle is hardcoded as the fallback compression algorithm. As a
consequence, on systems where another compression algorithm is chosen
(e.g. CRYPTO_ZSTD), the lzo kernel module becomes unused, while still
having to be built/loaded.

This patch removes the hardcoded lzo-rle dependency and allows the user
to select the default compression algorithm for zram at build time. The
previous behaviour is kept, as the default algorithm is still lzo-rle.

Link: https://lkml.kernel.org/r/20201207121245.50529-1-rsalvaterra@gmail.com
Signed-off-by: Rui Salvaterra <rsalvaterra@gmail.com>
Suggested-by: Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com>
Suggested-by: Minchan Kim <minchan@kernel.org>
Acked-by: Minchan Kim <minchan@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

zcomp: Use ARRAY_SIZE() for backends list

Instead of keeping NULL terminated array switch to use ARRAY_SIZE()
which helps to further clean up.

Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Reviewed-by: Andrew Morton <akpm@linux-foundation.org>
Acked-by: Minchan Kim <minchan@kernel.org>
Cc: Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com>
Cc: Jens Axboe <axboe@kernel.dk>
Cc: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Link: http://lkml.kernel.org/r/20200508100758.51644-1-andriy.shevchenko@linux.intel.com
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

zram: Use local lock to protect per-CPU data

The zcomp driver uses per-CPU compression. The per-CPU data pointer is
acquired with get_cpu_ptr() which implicitly disables preemption.
It allocates memory inside the preempt disabled region which conflicts
with the PREEMPT_RT semantics.

Replace the implicit preemption control with an explicit local lock.
This allows RT kernels to substitute it with a real per CPU lock, which
serializes the access but keeps the code section preemptible. On non RT
kernels this maps to preempt_disable() as before, i.e. no functional
change.

[bigeasy: Use local_lock(), description, drop reordering]

Signed-off-by: Mike Galbraith <umgwanakikbuti@gmail.com>
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Acked-by: Peter Zijlstra <peterz@infradead.org>
Link: https://lore.kernel.org/r/20200527201119.1692513-8-bigeasy@linutronix.de

zram: Allocate struct zcomp_strm as per-CPU memory

zcomp::stream is a per-CPU pointer, pointing to struct zcomp_strm
which contains two pointers. Having struct zcomp_strm allocated
directly as per-CPU memory would avoid one additional memory
allocation and a pointer dereference. This also simplifies the
addition of a local_lock to struct zcomp_strm.

Allocate zcomp::stream directly as per-CPU memory.

Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Acked-by: Peter Zijlstra <peterz@infradead.org>
Link: https://lore.kernel.org/r/20200527201119.1692513-7-bigeasy@linutronix.de

treewide: Replace GPLv2 boilerplate/reference with SPDX - rule 152

Based on 1 normalized pattern(s):

this program is free software you can redistribute it and or modify
it under the terms of the gnu general public license as published by
the free software foundation either version 2 of the license or at
your option any later version

extracted by the scancode license scanner the SPDX license identifier

GPL-2.0-or-later

has been chosen to replace the boilerplate/reference in 3029 file(s).

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Allison Randal <allison@lohutok.net>
Cc: linux-spdx@vger.kernel.org
Link: https://lkml.kernel.org/r/20190527070032.746973796@linutronix.de
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

lib/lzo: separate lzo-rle from lzo

To prevent any issues with persistent data, separate lzo-rle from lzo so
that it is treated as a separate algorithm, and lzo is still available.

Link: http://lkml.kernel.org/r/20190205155944.16007-3-dave.rodgman@arm.com
Signed-off-by: Dave Rodgman <dave.rodgman@arm.com>
Cc: David S. Miller <davem@davemloft.net>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Herbert Xu <herbert@gondor.apana.org.au>
Cc: Markus F.X.J. Oberhumer <markus@oberhumer.com>
Cc: Matt Sealey <matt.sealey@arm.com>
Cc: Minchan Kim <minchan@kernel.org>
Cc: Nitin Gupta <nitingupta910@gmail.com>
Cc: Richard Purdie <rpurdie@openedhand.com>
Cc: Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com>
Cc: Sonny Rao <sonnyrao@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

zram: remove zlib from the list of recommended algorithms

ZSTD tends to outperform deflate/inflate, thus we remove zlib from the
list of recommended algorithms and recommend zstd instead.

Link: http://lkml.kernel.org/r/20170912050005.3247-2-sergey.senozhatsky@gmail.com
Signed-off-by: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
Suggested-by: Minchan Kim <minchan@kernel.org>
Acked-by: Minchan Kim <minchan@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

zram: add zstd to the supported algorithms list

Add ZSTD to the list of supported compression algorithms.

ZRAM fio perf test:

LZO DEFLATE ZSTD

#jobs1
WRITE: (2180MB/s) (77.2MB/s) (1429MB/s)
WRITE: (1617MB/s) (77.7MB/s) (1202MB/s)
READ: (426MB/s) (595MB/s) (1181MB/s)
READ: (422MB/s) (572MB/s) (1020MB/s)
READ: (318MB/s) (67.8MB/s) (563MB/s)
WRITE: (318MB/s) (67.9MB/s) (564MB/s)
READ: (336MB/s) (68.3MB/s) (583MB/s)
WRITE: (335MB/s) (68.2MB/s) (582MB/s)
#jobs2
WRITE: (3441MB/s) (152MB/s) (2141MB/s)
WRITE: (2507MB/s) (147MB/s) (1888MB/s)
READ: (801MB/s) (1146MB/s) (1890MB/s)
READ: (767MB/s) (1096MB/s) (2073MB/s)
READ: (621MB/s) (126MB/s) (1009MB/s)
WRITE: (621MB/s) (126MB/s) (1009MB/s)
READ: (656MB/s) (125MB/s) (1075MB/s)
WRITE: (657MB/s) (126MB/s) (1077MB/s)
#jobs3
WRITE: (4772MB/s) (225MB/s) (3394MB/s)
WRITE: (3905MB/s) (211MB/s) (2939MB/s)
READ: (1216MB/s) (1608MB/s) (3218MB/s)
READ: (1159MB/s) (1431MB/s) (2981MB/s)
READ: (906MB/s) (156MB/s) (1457MB/s)
WRITE: (907MB/s) (156MB/s) (1458MB/s)
READ: (953MB/s) (158MB/s) (1595MB/s)
WRITE: (952MB/s) (157MB/s) (1593MB/s)
#jobs4
WRITE: (6036MB/s) (265MB/s) (4469MB/s)
WRITE: (5059MB/s) (263MB/s) (3951MB/s)
READ: (1618MB/s) (2066MB/s) (4276MB/s)
READ: (1573MB/s) (1942MB/s) (3830MB/s)
READ: (1202MB/s) (227MB/s) (1971MB/s)
WRITE: (1200MB/s) (227MB/s) (1968MB/s)
READ: (1265MB/s) (226MB/s) (2116MB/s)
WRITE: (1264MB/s) (226MB/s) (2114MB/s)
#jobs5
WRITE: (5339MB/s) (233MB/s) (3781MB/s)
WRITE: (4298MB/s) (234MB/s) (3276MB/s)
READ: (1626MB/s) (2048MB/s) (4081MB/s)
READ: (1567MB/s) (1929MB/s) (3758MB/s)
READ: (1174MB/s) (205MB/s) (1747MB/s)
WRITE: (1173MB/s) (204MB/s) (1746MB/s)
READ: (1214MB/s) (208MB/s) (1890MB/s)
WRITE: (1215MB/s) (208MB/s) (1892MB/s)
#jobs6
WRITE: (5666MB/s) (270MB/s) (4338MB/s)
WRITE: (4828MB/s) (267MB/s) (3772MB/s)
READ: (1803MB/s) (2058MB/s) (4946MB/s)
READ: (1805MB/s) (2156MB/s) (4711MB/s)
READ: (1334MB/s) (235MB/s) (2135MB/s)
WRITE: (1335MB/s) (235MB/s) (2137MB/s)
READ: (1364MB/s) (236MB/s) (2268MB/s)
WRITE: (1365MB/s) (237MB/s) (2270MB/s)
#jobs7
WRITE: (5474MB/s) (270MB/s) (4300MB/s)
WRITE: (4666MB/s) (266MB/s) (3817MB/s)
READ: (2022MB/s) (2319MB/s) (5472MB/s)
READ: (1924MB/s) (2260MB/s) (5031MB/s)
READ: (1369MB/s) (242MB/s) (2153MB/s)
WRITE: (1370MB/s) (242MB/s) (2155MB/s)
READ: (1499MB/s) (246MB/s) (2310MB/s)
WRITE: (1497MB/s) (246MB/s) (2307MB/s)
#jobs8
WRITE: (5558MB/s) (273MB/s) (4439MB/s)
WRITE: (4763MB/s) (271MB/s) (3918MB/s)
READ: (2201MB/s) (2599MB/s) (6062MB/s)
READ: (2105MB/s) (2463MB/s) (5413MB/s)
READ: (1490MB/s) (252MB/s) (2238MB/s)
WRITE: (1488MB/s) (252MB/s) (2236MB/s)
READ: (1566MB/s) (254MB/s) (2434MB/s)
WRITE: (1568MB/s) (254MB/s) (2437MB/s)
#jobs9
WRITE: (5120MB/s) (264MB/s) (4035MB/s)
WRITE: (4531MB/s) (267MB/s) (3740MB/s)
READ: (1940MB/s) (2258MB/s) (4986MB/s)
READ: (2024MB/s) (2387MB/s) (4871MB/s)
READ: (1343MB/s) (246MB/s) (2038MB/s)
WRITE: (1342MB/s) (246MB/s) (2037MB/s)
READ: (1553MB/s) (238MB/s) (2243MB/s)
WRITE: (1552MB/s) (238MB/s) (2242MB/s)
#jobs10
WRITE: (5345MB/s) (271MB/s) (3988MB/s)
WRITE: (4750MB/s) (254MB/s) (3668MB/s)
READ: (1876MB/s) (2363MB/s) (5150MB/s)
READ: (1990MB/s) (2256MB/s) (5080MB/s)
READ: (1355MB/s) (250MB/s) (2019MB/s)
WRITE: (1356MB/s) (251MB/s) (2020MB/s)
READ: (1490MB/s) (252MB/s) (2202MB/s)
WRITE: (1488MB/s) (252MB/s) (2199MB/s)

jobs1 perfstat
instructions 52,065,555,710 ( 0.79) 855,731,114,587 ( 2.64) 54,280,709,944 ( 1.40)
branches 14,020,427,116 ( 725.847) 101,733,449,582 (1074.521) 11,170,591,067 ( 992.869)
branch-misses 22,626,174 ( 0.16%) 274,197,885 ( 0.27%) 25,915,805 ( 0.23%)
jobs2 perfstat
instructions 103,633,110,402 ( 0.75) 1,710,822,100,914 ( 2.59) 107,879,874,104 ( 1.28)
branches 27,931,237,282 ( 679.203) 203,298,267,479 (1037.326) 22,185,350,842 ( 884.427)
branch-misses 46,103,811 ( 0.17%) 533,747,204 ( 0.26%) 49,682,483 ( 0.22%)
jobs3 perfstat
instructions 154,857,283,657 ( 0.76) 2,565,748,974,197 ( 2.57) 161,515,435,813 ( 1.31)
branches 41,759,490,355 ( 670.529) 304,905,605,277 ( 978.765) 33,215,805,907 ( 888.003)
branch-misses 74,263,293 ( 0.18%) 759,746,240 ( 0.25%) 76,841,196 ( 0.23%)
jobs4 perfstat
instructions 206,215,849,076 ( 0.75) 3,420,169,460,897 ( 2.60) 215,003,061,664 ( 1.31)
branches 55,632,141,739 ( 666.501) 406,394,977,433 ( 927.241) 44,214,322,251 ( 883.532)
branch-misses 102,287,788 ( 0.18%) 1,098,617,314 ( 0.27%) 103,891,040 ( 0.23%)
jobs5 perfstat
instructions 258,711,315,588 ( 0.67) 4,275,657,533,244 ( 2.23) 269,332,235,685 ( 1.08)
branches 69,802,821,166 ( 588.823) 507,996,211,252 ( 797.036) 55,450,846,129 ( 735.095)
branch-misses 129,217,214 ( 0.19%) 1,243,284,991 ( 0.24%) 173,512,278 ( 0.31%)
jobs6 perfstat
instructions 312,796,166,008 ( 0.61) 5,133,896,344,660 ( 2.02) 323,658,769,588 ( 1.04)
branches 84,372,488,583 ( 520.541) 610,310,494,402 ( 697.642) 66,683,292,992 ( 693.939)
branch-misses 159,438,978 ( 0.19%) 1,396,368,563 ( 0.23%) 174,406,934 ( 0.26%)
jobs7 perfstat
instructions 363,211,372,930 ( 0.56) 5,988,205,600,879 ( 1.75) 377,824,674,156 ( 0.93)
branches 98,057,013,765 ( 463.117) 711,841,255,974 ( 598.762) 77,879,009,954 ( 600.443)
branch-misses 199,513,153 ( 0.20%) 1,507,651,077 ( 0.21%) 248,203,369 ( 0.32%)
jobs8 perfstat
instructions 413,960,354,615 ( 0.52) 6,842,918,558,378 ( 1.45) 431,938,486,581 ( 0.83)
branches 111,812,574,884 ( 414.224) 813,299,084,518 ( 491.173) 89,062,699,827 ( 517.795)
branch-misses 233,584,845 ( 0.21%) 1,531,593,921 ( 0.19%) 286,818,489 ( 0.32%)
jobs9 perfstat
instructions 465,976,220,300 ( 0.53) 7,698,467,237,372 ( 1.47) 486,352,600,321 ( 0.84)
branches 125,931,456,162 ( 424.063) 915,207,005,715 ( 498.192) 100,370,404,090 ( 517.439)
branch-misses 256,992,445 ( 0.20%) 1,782,809,816 ( 0.19%) 345,239,380 ( 0.34%)
jobs10 perfstat
instructions 517,406,372,715 ( 0.53) 8,553,527,312,900 ( 1.48) 540,732,653,094 ( 0.84)
branches 139,839,780,676 ( 427.732) 1,016,737,699,389 ( 503.172) 111,696,557,638 ( 516.750)
branch-misses 259,595,561 ( 0.19%) 1,952,570,279 ( 0.19%) 357,818,661 ( 0.32%)

seconds elapsed 20.630411534 96.084546565 12.743373571
seconds elapsed 22.292627625 100.984155001 14.407413560
seconds elapsed 22.396016966 110.344880848 14.032201392
seconds elapsed 22.517330949 113.351459170 14.243074935
seconds elapsed 28.548305104 156.515193765 19.159286861
seconds elapsed 30.453538116 164.559937678 19.362492717
seconds elapsed 33.467108086 188.486827481 21.492612173
seconds elapsed 35.617727591 209.602677783 23.256422492
seconds elapsed 42.584239509 243.959902566 28.458540338
seconds elapsed 47.683632526 269.635248851 31.542404137

Over all, ZSTD has slower WRITE, but much faster READ (perhaps
a static compression buffer used during the test helped ZSTD a
lot), which results in faster test results.

Memory consumption (zram mm_stat file):

zram LZO mm_stat
mm_stat (jobs1): 2147483648 23068672 33558528 0 33558528 0 0
mm_stat (jobs2): 2147483648 23068672 33558528 0 33558528 0 0
mm_stat (jobs3): 2147483648 23068672 33558528 0 33562624 0 0
mm_stat (jobs4): 2147483648 23068672 33558528 0 33558528 0 0
mm_stat (jobs5): 2147483648 23068672 33558528 0 33558528 0 0
mm_stat (jobs6): 2147483648 23068672 33558528 0 33562624 0 0
mm_stat (jobs7): 2147483648 23068672 33558528 0 33566720 0 0
mm_stat (jobs8): 2147483648 23068672 33558528 0 33558528 0 0
mm_stat (jobs9): 2147483648 23068672 33558528 0 33558528 0 0
mm_stat (jobs10): 2147483648 23068672 33558528 0 33562624 0 0

zram DEFLATE mm_stat
mm_stat (jobs1): 2147483648 16252928 25178112 0 25178112 0 0
mm_stat (jobs2): 2147483648 16252928 25178112 0 25178112 0 0
mm_stat (jobs3): 2147483648 16252928 25178112 0 25178112 0 0
mm_stat (jobs4): 2147483648 16252928 25178112 0 25178112 0 0
mm_stat (jobs5): 2147483648 16252928 25178112 0 25178112 0 0
mm_stat (jobs6): 2147483648 16252928 25178112 0 25178112 0 0
mm_stat (jobs7): 2147483648 16252928 25178112 0 25190400 0 0
mm_stat (jobs8): 2147483648 16252928 25178112 0 25190400 0 0
mm_stat (jobs9): 2147483648 16252928 25178112 0 25178112 0 0
mm_stat (jobs10): 2147483648 16252928 25178112 0 25178112 0 0

zram ZSTD mm_stat
mm_stat (jobs1): 2147483648 11010048 16781312 0 16781312 0 0
mm_stat (jobs2): 2147483648 11010048 16781312 0 16781312 0 0
mm_stat (jobs3): 2147483648 11010048 16781312 0 16785408 0 0
mm_stat (jobs4): 2147483648 11010048 16781312 0 16781312 0 0
mm_stat (jobs5): 2147483648 11010048 16781312 0 16781312 0 0
mm_stat (jobs6): 2147483648 11010048 16781312 0 16781312 0 0
mm_stat (jobs7): 2147483648 11010048 16781312 0 16781312 0 0
mm_stat (jobs8): 2147483648 11010048 16781312 0 16781312 0 0
mm_stat (jobs9): 2147483648 11010048 16781312 0 16785408 0 0
mm_stat (jobs10): 2147483648 11010048 16781312 0 16781312 0 0

==================================================================================

Official benchmarks [1]:

Compressor name Ratio Compression Decompress.
zstd 1.1.3 -1 2.877 430 MB/s 1110 MB/s
zlib 1.2.8 -1 2.743 110 MB/s 400 MB/s
brotli 0.5.2 -0 2.708 400 MB/s 430 MB/s
quicklz 1.5.0 -1 2.238 550 MB/s 710 MB/s
lzo1x 2.09 -1 2.108 650 MB/s 830 MB/s
lz4 1.7.5 2.101 720 MB/s 3600 MB/s
snappy 1.1.3 2.091 500 MB/s 1650 MB/s
lzf 3.6 -1 2.077 400 MB/s 860 MB/s

Minchan said:

: I did test with my sample data and compared zstd with deflate. zstd's
: compress ratio is lower a little bit but compression speed is much faster
: 3 times more and decompress speed is too 2 times more. With different
: data, it is different but overall, zstd would be better for speed at the
: cost of a little lower compress ratio(about 5%) so I believe it's worth to
: replace deflate.

[1] https://github.com/facebook/zstd

Link: http://lkml.kernel.org/r/20170912050005.3247-1-sergey.senozhatsky@gmail.com
Signed-off-by: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
Acked-by: Minchan Kim <minchan@kernel.org>
Tested-by: Minchan Kim <minchan@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

zram: use __sysfs_match_string() helper

Use __sysfs_match_string() helper instead of open coded variant.

Link: http://lkml.kernel.org/r/20170609120835.22156-1-andriy.shevchenko@linux.intel.com
Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Reviewed-by: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
Acked-by: Minchan Kim <minchan@kernel.org>
Cc: Nitin Gupta <ngupta@vflare.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

zram: Convert to hotplug state machine

Install the callbacks via the state machine with multi instance support and let
the core invoke the callbacks on the already online CPUs.

[bigeasy: wire up the multi instance stuff]
Signed-off-by: Anna-Maria Gleixner <anna-maria@linutronix.de>
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com>
Cc: Minchan Kim <minchan@kernel.org>
Cc: rt@linutronix.de
Cc: Nitin Gupta <ngupta@vflare.org>
Link: http://lkml.kernel.org/r/20161126231350.10321-19-bigeasy@linutronix.de
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>

zram: drop gfp_t from zcomp_strm_alloc()

We now allocate streams from CPU_UP hot-plug path, there are no
context-dependent stream allocations anymore and we can schedule from
zcomp_strm_alloc(). Use GFP_KERNEL directly and drop a gfp_t parameter.

Link: http://lkml.kernel.org/r/20160531122017.2878-9-sergey.senozhatsky@gmail.com
Signed-off-by: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
Acked-by: Minchan Kim <minchan@kernel.org>
Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

zram: add more compression algorithms

Add "deflate", "lz4hc", "842" algorithms to the list of known
compression backends. The real availability of those algorithms,
however, depends on the corresponding CONFIG_CRYPTO_FOO config options.

[sergey.senozhatsky@gmail.com: zram-add-more-compression-algorithms-v3]
Link: http://lkml.kernel.org/r/20160604024902.11778-7-sergey.senozhatsky@gmail.com
Link: http://lkml.kernel.org/r/20160531122017.2878-8-sergey.senozhatsky@gmail.com
Signed-off-by: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
Acked-by: Minchan Kim <minchan@kernel.org>
Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

zram: delete custom lzo/lz4

Remove lzo/lz4 backends, we use crypto API now.

[sergey.senozhatsky@gmail.com: zram-delete-custom-lzo-lz4-v3]
Link: http://lkml.kernel.org/r/20160604024902.11778-6-sergey.senozhatsky@gmail.com
Link: http://lkml.kernel.org/r/20160531122017.2878-7-sergey.senozhatsky@gmail.com
Signed-off-by: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
Acked-by: Minchan Kim <minchan@kernel.org>
Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

zram: use crypto api to check alg availability

There is no way to get a string with all the crypto comp algorithms
supported by the crypto comp engine, so we need to maintain our own
backends list. At the same time we additionally need to use
crypto_has_comp() to make sure that the user has requested a compression
algorithm that is recognized by the crypto comp engine. Relying on
/proc/crypto is not an options here, because it does not show
not-yet-inserted compression modules.

Example:

modprobe zram
cat /proc/crypto | grep -i lz4
modprobe lz4
cat /proc/crypto | grep -i lz4
name : lz4
driver : lz4-generic
module : lz4

So the user can't tell exactly if the lz4 is really supported from
/proc/crypto output, unless someone or something has loaded it.

This patch also adds crypto_has_comp() to zcomp_available_show(). We
store all the compression algorithms names in zcomp's `backends' array,
regardless the CONFIG_CRYPTO_FOO configuration, but show only those that
are also supported by crypto engine. This helps user to know the exact
list of compression algorithms that can be used.

Example:
module lz4 is not loaded yet, but is supported by the crypto
engine. /proc/crypto has no information on this module, while
zram's `comp_algorithm' lists it:

cat /proc/crypto | grep -i lz4

cat /sys/block/zram0/comp_algorithm
[lzo] lz4 deflate lz4hc 842

We still use the `backends' array to determine if the requested
compression backend is known to crypto api. This array, however, may not
contain some entries, therefore as the last step we call crypto_has_comp()
function which attempts to insmod the requested compression algorithm to
determine if crypto api supports it. The advantage of this method is that
now we permit the usage of out-of-tree crypto compression modules
(implementing S/W or H/W compression).

[sergey.senozhatsky@gmail.com: zram-use-crypto-api-to-check-alg-availability-v3]
Link: http://lkml.kernel.org/r/20160604024902.11778-4-sergey.senozhatsky@gmail.com
Link: http://lkml.kernel.org/r/20160531122017.2878-5-sergey.senozhatsky@gmail.com
Signed-off-by: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
Acked-by: Minchan Kim <minchan@kernel.org>
Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Signed-off-by: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

zram: switch to crypto compress API

We don't have an idle zstreams list anymore and our write path now works
absolutely differently, preventing preemption during compression. This
removes possibilities of read paths preempting writes at wrong places
(which could badly affect the performance of both paths) and at the same
time opens the door for a move from custom LZO/LZ4 compression backends
implementation to a more generic one, using crypto compress API.

Joonsoo Kim [1] attempted to do this a while ago, but faced with the
need of introducing a new crypto API interface. The root cause was the
fact that crypto API compression algorithms require a compression stream
structure (in zram terminology) for both compression and decompression
ops, while in reality only several of compression algorithms really need
it. This resulted in a concept of context-less crypto API compression
backends [2]. Both write and read paths, though, would have been
executed with the preemption enabled, which in the worst case could have
resulted in a decreased worst-case performance, e.g. consider the
following case:

CPU0

zram_write()
spin_lock()
take the last idle stream
spin_unlock()

<< preempted >>

zram_read()
spin_lock()
no idle streams
spin_unlock()
schedule()

resuming zram_write compression()

but it took me some time to realize that, and it took even longer to
evolve zram and to make it ready for crypto API. The key turned out to be
-- drop the idle streams list entirely. Without the idle streams list we
are free to use compression algorithms that require compression stream for
decompression (read), because streams are now placed in per-cpu data and
each write path has to disable preemption for compression op, almost
completely eliminating the aforementioned case (technically, we still have
a small chance, because write path has a fast and a slow paths and the
slow path is executed with the preemption enabled; but the frequency of
failed fast path is too low).

TEST
====

- 4 CPUs, x86_64 system
- 3G zram, lzo
- fio tests: read, randread, write, randwrite, rw, randrw

test script [3] command:
ZRAM_SIZE=3G LOG_SUFFIX=XXXX FIO_LOOPS=5 ./zram-fio-test.sh

BASE PATCHED
jobs1
READ: 2527.2MB/s 2482.7MB/s
READ: 2102.7MB/s 2045.0MB/s
WRITE: 1284.3MB/s 1324.3MB/s
WRITE: 1080.7MB/s 1101.9MB/s
READ: 430125KB/s 437498KB/s
WRITE: 430538KB/s 437919KB/s
READ: 399593KB/s 403987KB/s
WRITE: 399910KB/s 404308KB/s
jobs2
READ: 8133.5MB/s 7854.8MB/s
READ: 7086.6MB/s 6912.8MB/s
WRITE: 3177.2MB/s 3298.3MB/s
WRITE: 2810.2MB/s 2871.4MB/s
READ: 1017.6MB/s 1023.4MB/s
WRITE: 1018.2MB/s 1023.1MB/s
READ: 977836KB/s 984205KB/s
WRITE: 979435KB/s 985814KB/s
jobs3
READ: 13557MB/s 13391MB/s
READ: 11876MB/s 11752MB/s
WRITE: 4641.5MB/s 4682.1MB/s
WRITE: 4164.9MB/s 4179.3MB/s
READ: 1453.8MB/s 1455.1MB/s
WRITE: 1455.1MB/s 1458.2MB/s
READ: 1387.7MB/s 1395.7MB/s
WRITE: 1386.1MB/s 1394.9MB/s
jobs4
READ: 20271MB/s 20078MB/s
READ: 18033MB/s 17928MB/s
WRITE: 6176.8MB/s 6180.5MB/s
WRITE: 5686.3MB/s 5705.3MB/s
READ: 2009.4MB/s 2006.7MB/s
WRITE: 2007.5MB/s 2004.9MB/s
READ: 1929.7MB/s 1935.6MB/s
WRITE: 1926.8MB/s 1932.6MB/s
jobs5
READ: 18823MB/s 19024MB/s
READ: 18968MB/s 19071MB/s
WRITE: 6191.6MB/s 6372.1MB/s
WRITE: 5818.7MB/s 5787.1MB/s
READ: 2011.7MB/s 1981.3MB/s
WRITE: 2011.4MB/s 1980.1MB/s
READ: 1949.3MB/s 1935.7MB/s
WRITE: 1940.4MB/s 1926.1MB/s
jobs6
READ: 21870MB/s 21715MB/s
READ: 19957MB/s 19879MB/s
WRITE: 6528.4MB/s 6537.6MB/s
WRITE: 6098.9MB/s 6073.6MB/s
READ: 2048.6MB/s 2049.9MB/s
WRITE: 2041.7MB/s 2042.9MB/s
READ: 2013.4MB/s 1990.4MB/s
WRITE: 2009.4MB/s 1986.5MB/s
jobs7
READ: 21359MB/s 21124MB/s
READ: 19746MB/s 19293MB/s
WRITE: 6660.4MB/s 6518.8MB/s
WRITE: 6211.6MB/s 6193.1MB/s
READ: 2089.7MB/s 2080.6MB/s
WRITE: 2085.8MB/s 2076.5MB/s
READ: 2041.2MB/s 2052.5MB/s
WRITE: 2037.5MB/s 2048.8MB/s
jobs8
READ: 20477MB/s 19974MB/s
READ: 18922MB/s 18576MB/s
WRITE: 6851.9MB/s 6788.3MB/s
WRITE: 6407.7MB/s 6347.5MB/s
READ: 2134.8MB/s 2136.1MB/s
WRITE: 2132.8MB/s 2134.4MB/s
READ: 2074.2MB/s 2069.6MB/s
WRITE: 2087.3MB/s 2082.4MB/s
jobs9
READ: 19797MB/s 19994MB/s
READ: 18806MB/s 18581MB/s
WRITE: 6878.7MB/s 6822.7MB/s
WRITE: 6456.8MB/s 6447.2MB/s
READ: 2141.1MB/s 2154.7MB/s
WRITE: 2144.4MB/s 2157.3MB/s
READ: 2084.1MB/s 2085.1MB/s
WRITE: 2091.5MB/s 2092.5MB/s
jobs10
READ: 19794MB/s 19784MB/s
READ: 18794MB/s 18745MB/s
WRITE: 6984.4MB/s 6676.3MB/s
WRITE: 6532.3MB/s 6342.7MB/s
READ: 2150.6MB/s 2155.4MB/s
WRITE: 2156.8MB/s 2161.5MB/s
READ: 2106.4MB/s 2095.6MB/s
WRITE: 2109.7MB/s 2098.4MB/s

BASE PATCHED
jobs1 perfstat
stalled-cycles-frontend 102,480,595,419 ( 41.53%) 114,508,864,804 ( 46.92%)
stalled-cycles-backend 51,941,417,832 ( 21.05%) 46,836,112,388 ( 19.19%)
instructions 283,612,054,215 ( 1.15) 283,918,134,959 ( 1.16)
branches 56,372,560,385 ( 724.923) 56,449,814,753 ( 733.766)
branch-misses 374,826,000 ( 0.66%) 326,935,859 ( 0.58%)
jobs2 perfstat
stalled-cycles-frontend 155,142,745,777 ( 40.99%) 164,170,979,198 ( 43.82%)
stalled-cycles-backend 70,813,866,387 ( 18.71%) 66,456,858,165 ( 17.74%)
instructions 463,436,648,173 ( 1.22) 464,221,890,191 ( 1.24)
branches 91,088,733,902 ( 760.088) 91,278,144,546 ( 769.133)
branch-misses 504,460,363 ( 0.55%) 394,033,842 ( 0.43%)
jobs3 perfstat
stalled-cycles-frontend 201,300,397,212 ( 39.84%) 223,969,902,257 ( 44.44%)
stalled-cycles-backend 87,712,593,974 ( 17.36%) 81,618,888,712 ( 16.19%)
instructions 642,869,545,023 ( 1.27) 644,677,354,132 ( 1.28)
branches 125,724,560,594 ( 690.682) 126,133,159,521 ( 694.542)
branch-misses 527,941,798 ( 0.42%) 444,782,220 ( 0.35%)
jobs4 perfstat
stalled-cycles-frontend 246,701,197,429 ( 38.12%) 280,076,030,886 ( 43.29%)
stalled-cycles-backend 119,050,341,112 ( 18.40%) 110,955,641,671 ( 17.15%)
instructions 822,716,962,127 ( 1.27) 825,536,969,320 ( 1.28)
branches 160,590,028,545 ( 688.614) 161,152,996,915 ( 691.068)
branch-misses 650,295,287 ( 0.40%) 550,229,113 ( 0.34%)
jobs5 perfstat
stalled-cycles-frontend 298,958,462,516 ( 38.30%) 344,852,200,358 ( 44.16%)
stalled-cycles-backend 137,558,742,122 ( 17.62%) 129,465,067,102 ( 16.58%)
instructions 1,005,714,688,752 ( 1.29) 1,007,657,999,432 ( 1.29)
branches 195,988,773,962 ( 697.730) 196,446,873,984 ( 700.319)
branch-misses 695,818,940 ( 0.36%) 624,823,263 ( 0.32%)
jobs6 perfstat
stalled-cycles-frontend 334,497,602,856 ( 36.71%) 387,590,419,779 ( 42.38%)
stalled-cycles-backend 163,539,365,335 ( 17.95%) 152,640,193,639 ( 16.69%)
instructions 1,184,738,177,851 ( 1.30) 1,187,396,281,677 ( 1.30)
branches 230,592,915,640 ( 702.902) 231,253,802,882 ( 702.356)
branch-misses 747,934,786 ( 0.32%) 643,902,424 ( 0.28%)
jobs7 perfstat
stalled-cycles-frontend 396,724,684,187 ( 37.71%) 460,705,858,952 ( 43.84%)
stalled-cycles-backend 188,096,616,496 ( 17.88%) 175,785,787,036 ( 16.73%)
instructions 1,364,041,136,608 ( 1.30) 1,366,689,075,112 ( 1.30)
branches 265,253,096,936 ( 700.078) 265,890,524,883 ( 702.839)
branch-misses 784,991,589 ( 0.30%) 729,196,689 ( 0.27%)
jobs8 perfstat
stalled-cycles-frontend 440,248,299,870 ( 36.92%) 509,554,793,816 ( 42.46%)
stalled-cycles-backend 222,575,930,616 ( 18.67%) 213,401,248,432 ( 17.78%)
instructions 1,542,262,045,114 ( 1.29) 1,545,233,932,257 ( 1.29)
branches 299,775,178,439 ( 697.666) 300,528,458,505 ( 694.769)
branch-misses 847,496,084 ( 0.28%) 748,794,308 ( 0.25%)
jobs9 perfstat
stalled-cycles-frontend 506,269,882,480 ( 37.86%) 592,798,032,820 ( 44.43%)
stalled-cycles-backend 253,192,498,861 ( 18.93%) 233,727,666,185 ( 17.52%)
instructions 1,721,985,080,913 ( 1.29) 1,724,666,236,005 ( 1.29)
branches 334,517,360,255 ( 694.134) 335,199,758,164 ( 697.131)
branch-misses 873,496,730 ( 0.26%) 815,379,236 ( 0.24%)
jobs10 perfstat
stalled-cycles-frontend 549,063,363,749 ( 37.18%) 651,302,376,662 ( 43.61%)
stalled-cycles-backend 281,680,986,810 ( 19.07%) 277,005,235,582 ( 18.55%)
instructions 1,901,859,271,180 ( 1.29) 1,906,311,064,230 ( 1.28)
branches 369,398,536,153 ( 694.004) 370,527,696,358 ( 688.409)
branch-misses 967,929,335 ( 0.26%) 890,125,056 ( 0.24%)

BASE PATCHED
seconds elapsed 79.421641008 78.735285546
seconds elapsed 61.471246133 60.869085949
seconds elapsed 62.317058173 62.224188495
seconds elapsed 60.030739363 60.081102518
seconds elapsed 74.070398362 74.317582865
seconds elapsed 84.985953007 85.414364176
seconds elapsed 97.724553255 98.173311344
seconds elapsed 109.488066758 110.268399318
seconds elapsed 122.768189405 122.967164498
seconds elapsed 135.130035105 136.934770801

On my other system (8 x86_64 CPUs, short version of test results):

BASE PATCHED
seconds elapsed 19.518065994 19.806320662
seconds elapsed 15.172772749 15.594718291
seconds elapsed 13.820925970 13.821708564
seconds elapsed 13.293097816 14.585206405
seconds elapsed 16.207284118 16.064431606
seconds elapsed 17.958376158 17.771825767
seconds elapsed 19.478009164 19.602961508
seconds elapsed 21.347152811 21.352318709
seconds elapsed 24.478121126 24.171088735
seconds elapsed 26.865057442 26.767327618

So performance-wise the numbers are quite similar.

Also update zcomp interface to be more aligned with the crypto API.

[1] http://marc.info/?l=linux-kernel&m=144480832108927&w=2
[2] http://marc.info/?l=linux-kernel&m=145379613507518&w=2
[3] https://github.com/sergey-senozhatsky/zram-perf-test

Link: http://lkml.kernel.org/r/20160531122017.2878-3-sergey.senozhatsky@gmail.com
Signed-off-by: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
Suggested-by: Minchan Kim <minchan@kernel.org>
Suggested-by: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Acked-by: Minchan Kim <minchan@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

zram: rename zstrm find-release functions

This has started as a 'add zlib support' work, but after some thinking I
saw no blockers for a bigger change -- a switch to crypto API.

We don't have an idle zstreams list anymore and our write path now works
absolutely differently, preventing preemption during compression. This
removes possibilities of read paths preempting writes at wrong places
and opens the door for a move from custom LZO/LZ4 compression backends
implementation to a more generic one, using crypto compress API.

This patch set also eliminates the need of a new context-less crypto API
interface, which was quite hard to sell, so we can move along faster.

benchmarks:

(x86_64, 4GB, zram-perf script)

perf reported run-time fio (max jobs=3). I performed fio test with the
increasing number of parallel jobs (max to 3) on a 3G zram device, using
`static' data and the following crypto comp algorithms:

842, deflate, lz4, lz4hc, lzo

the output was:

- test running time (which can tell us what algorithms performs faster)

and

- zram mm_stat (which tells the compressed memory size, max used memory, etc).

It's just for information. for example, LZ4HC has twice the running
time of LZO, but the compressed memory size is: 23592960 vs 34603008
bytes.

test-fio-zram-842
197.907655282 seconds time elapsed
201.623142884 seconds time elapsed
226.854291345 seconds time elapsed
test-fio-zram-DEFLATE
253.259516155 seconds time elapsed
258.148563401 seconds time elapsed
290.251909365 seconds time elapsed
test-fio-zram-LZ4
27.022598717 seconds time elapsed
29.580522717 seconds time elapsed
33.293463430 seconds time elapsed
test-fio-zram-LZ4HC
56.393954615 seconds time elapsed
74.904659747 seconds time elapsed
101.940998564 seconds time elapsed
test-fio-zram-LZO
28.155948075 seconds time elapsed
30.390036330 seconds time elapsed
34.455773159 seconds time elapsed

zram mm_stat-s (max fio jobs=3)

test-fio-zram-842
mm_stat (jobs1): 3221225472 673185792 690266112 0 690266112 0 0
mm_stat (jobs2): 3221225472 673185792 690266112 0 690266112 0 0
mm_stat (jobs3): 3221225472 673185792 690266112 0 690266112 0 0
test-fio-zram-DEFLATE
mm_stat (jobs1): 3221225472 24379392 37761024 0 37761024 0 0
mm_stat (jobs2): 3221225472 24379392 37761024 0 37761024 0 0
mm_stat (jobs3): 3221225472 24379392 37761024 0 37761024 0 0
test-fio-zram-LZ4
mm_stat (jobs1): 3221225472 23592960 37761024 0 37761024 0 0
mm_stat (jobs2): 3221225472 23592960 37761024 0 37761024 0 0
mm_stat (jobs3): 3221225472 23592960 37761024 0 37761024 0 0
test-fio-zram-LZ4HC
mm_stat (jobs1): 3221225472 23592960 37761024 0 37761024 0 0
mm_stat (jobs2): 3221225472 23592960 37761024 0 37761024 0 0
mm_stat (jobs3): 3221225472 23592960 37761024 0 37761024 0 0
test-fio-zram-LZO
mm_stat (jobs1): 3221225472 34603008 50335744 0 50335744 0 0
mm_stat (jobs2): 3221225472 34603008 50335744 0 50335744 0 0
mm_stat (jobs3): 3221225472 34603008 50335744 0 50339840 0 0

This patch (of 8):

We don't perform any zstream idle list lookup anymore, so
zcomp_strm_find()/zcomp_strm_release() names are not representative.

Rename to zcomp_stream_get()/zcomp_stream_put().

Link: http://lkml.kernel.org/r/20160531122017.2878-2-sergey.senozhatsky@gmail.com
Signed-off-by: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
Acked-by: Minchan Kim <minchan@kernel.org>
Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

zram: remove max_comp_streams internals

Remove the internal part of max_comp_streams interface, since we
switched to per-cpu streams. We will keep RW max_comp_streams attr
around, because:

a) we may (silently) switch back to idle compression streams list and
don't want to disturb user space

b) max_comp_streams attr must wait for the next 'lay off cycle'; we
give user space 2 years to adjust before we remove/downgrade the attr,
and there are already several attrs scheduled for removal in 4.11, so
it's too late for max_comp_streams.

This slightly change a user visible behaviour:

- First, reading from max_comp_stream file now will always return the
number of online CPUs.

- Second, writing to max_comp_stream will not take any effect.

Link: http://lkml.kernel.org/r/20160503165546.25201-1-sergey.senozhatsky@gmail.com
Signed-off-by: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
Cc: Minchan Kim <minchan@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

zram: user per-cpu compression streams

Remove idle streams list and keep compression streams in per-cpu data.
This removes two contented spin_lock()/spin_unlock() calls from write
path and also prevent write OP from being preempted while holding the
compression stream, which can cause slow downs.

For instance, let's assume that we have N cpus and N-2
max_comp_streams.TASK1 owns the last idle stream, TASK2-TASK3 come in
with the write requests:

TASK1 TASK2 TASK3
zram_bvec_write()
spin_lock
find stream
spin_unlock

compress

<<preempted>> zram_bvec_write()
spin_lock
find stream
spin_unlock
no_stream
schedule
zram_bvec_write()
spin_lock
find_stream
spin_unlock
no_stream
schedule
spin_lock
release stream
spin_unlock
wake up TASK2

not only TASK2 and TASK3 will not get the stream, TASK1 will be
preempted in the middle of its operation; while we would prefer it to
finish compression and release the stream.

Test environment: x86_64, 4 CPU box, 3G zram, lzo

The following fio tests were executed:
read, randread, write, randwrite, rw, randrw
with the increasing number of jobs from 1 to 10.

4 streams 8 streams per-cpu
===========================================================
jobs1
READ: 2520.1MB/s 2566.5MB/s 2491.5MB/s
READ: 2102.7MB/s 2104.2MB/s 2091.3MB/s
WRITE: 1355.1MB/s 1320.2MB/s 1378.9MB/s
WRITE: 1103.5MB/s 1097.2MB/s 1122.5MB/s
READ: 434013KB/s 435153KB/s 439961KB/s
WRITE: 433969KB/s 435109KB/s 439917KB/s
READ: 403166KB/s 405139KB/s 403373KB/s
WRITE: 403223KB/s 405197KB/s 403430KB/s
jobs2
READ: 7958.6MB/s 8105.6MB/s 8073.7MB/s
READ: 6864.9MB/s 6989.8MB/s 7021.8MB/s
WRITE: 2438.1MB/s 2346.9MB/s 3400.2MB/s
WRITE: 1994.2MB/s 1990.3MB/s 2941.2MB/s
READ: 981504KB/s 973906KB/s 1018.8MB/s
WRITE: 981659KB/s 974060KB/s 1018.1MB/s
READ: 937021KB/s 938976KB/s 987250KB/s
WRITE: 934878KB/s 936830KB/s 984993KB/s
jobs3
READ: 13280MB/s 13553MB/s 13553MB/s
READ: 11534MB/s 11785MB/s 11755MB/s
WRITE: 3456.9MB/s 3469.9MB/s 4810.3MB/s
WRITE: 3029.6MB/s 3031.6MB/s 4264.8MB/s
READ: 1363.8MB/s 1362.6MB/s 1448.9MB/s
WRITE: 1361.9MB/s 1360.7MB/s 1446.9MB/s
READ: 1309.4MB/s 1310.6MB/s 1397.5MB/s
WRITE: 1307.4MB/s 1308.5MB/s 1395.3MB/s
jobs4
READ: 20244MB/s 20177MB/s 20344MB/s
READ: 17886MB/s 17913MB/s 17835MB/s
WRITE: 4071.6MB/s 4046.1MB/s 6370.2MB/s
WRITE: 3608.9MB/s 3576.3MB/s 5785.4MB/s
READ: 1824.3MB/s 1821.6MB/s 1997.5MB/s
WRITE: 1819.8MB/s 1817.4MB/s 1992.5MB/s
READ: 1765.7MB/s 1768.3MB/s 1937.3MB/s
WRITE: 1767.5MB/s 1769.1MB/s 1939.2MB/s
jobs5
READ: 18663MB/s 18986MB/s 18823MB/s
READ: 16659MB/s 16605MB/s 16954MB/s
WRITE: 3912.4MB/s 3888.7MB/s 6126.9MB/s
WRITE: 3506.4MB/s 3442.5MB/s 5519.3MB/s
READ: 1798.2MB/s 1746.5MB/s 1935.8MB/s
WRITE: 1792.7MB/s 1740.7MB/s 1929.1MB/s
READ: 1727.6MB/s 1658.2MB/s 1917.3MB/s
WRITE: 1726.5MB/s 1657.2MB/s 1916.6MB/s
jobs6
READ: 21017MB/s 20922MB/s 21162MB/s
READ: 19022MB/s 19140MB/s 18770MB/s
WRITE: 3968.2MB/s 4037.7MB/s 6620.8MB/s
WRITE: 3643.5MB/s 3590.2MB/s 6027.5MB/s
READ: 1871.8MB/s 1880.5MB/s 2049.9MB/s
WRITE: 1867.8MB/s 1877.2MB/s 2046.2MB/s
READ: 1755.8MB/s 1710.3MB/s 1964.7MB/s
WRITE: 1750.5MB/s 1705.9MB/s 1958.8MB/s
jobs7
READ: 21103MB/s 20677MB/s 21482MB/s
READ: 18522MB/s 18379MB/s 19443MB/s
WRITE: 4022.5MB/s 4067.4MB/s 6755.9MB/s
WRITE: 3691.7MB/s 3695.5MB/s 5925.6MB/s
READ: 1841.5MB/s 1933.9MB/s 2090.5MB/s
WRITE: 1842.7MB/s 1935.3MB/s 2091.9MB/s
READ: 1832.4MB/s 1856.4MB/s 1971.5MB/s
WRITE: 1822.3MB/s 1846.2MB/s 1960.6MB/s
jobs8
READ: 20463MB/s 20194MB/s 20862MB/s
READ: 18178MB/s 17978MB/s 18299MB/s
WRITE: 4085.9MB/s 4060.2MB/s 7023.8MB/s
WRITE: 3776.3MB/s 3737.9MB/s 6278.2MB/s
READ: 1957.6MB/s 1944.4MB/s 2109.5MB/s
WRITE: 1959.2MB/s 1946.2MB/s 2111.4MB/s
READ: 1900.6MB/s 1885.7MB/s 2082.1MB/s
WRITE: 1896.2MB/s 1881.4MB/s 2078.3MB/s
jobs9
READ: 19692MB/s 19734MB/s 19334MB/s
READ: 17678MB/s 18249MB/s 17666MB/s
WRITE: 4004.7MB/s 4064.8MB/s 6990.7MB/s
WRITE: 3724.7MB/s 3772.1MB/s 6193.6MB/s
READ: 1953.7MB/s 1967.3MB/s 2105.6MB/s
WRITE: 1953.4MB/s 1966.7MB/s 2104.1MB/s
READ: 1860.4MB/s 1897.4MB/s 2068.5MB/s
WRITE: 1858.9MB/s 1895.9MB/s 2066.8MB/s
jobs10
READ: 19730MB/s 19579MB/s 19492MB/s
READ: 18028MB/s 18018MB/s 18221MB/s
WRITE: 4027.3MB/s 4090.6MB/s 7020.1MB/s
WRITE: 3810.5MB/s 3846.8MB/s 6426.8MB/s
READ: 1956.1MB/s 1994.6MB/s 2145.2MB/s
WRITE: 1955.9MB/s 1993.5MB/s 2144.8MB/s
READ: 1852.8MB/s 1911.6MB/s 2075.8MB/s
WRITE: 1855.7MB/s 1914.6MB/s 2078.1MB/s

perf stat

4 streams 8 streams per-cpu
====================================================================================================================
jobs1
stalled-cycles-frontend 23,174,811,209 ( 38.21%) 23,220,254,188 ( 38.25%) 23,061,406,918 ( 38.34%)
stalled-cycles-backend 11,514,174,638 ( 18.98%) 11,696,722,657 ( 19.27%) 11,370,852,810 ( 18.90%)
instructions 73,925,005,782 ( 1.22) 73,903,177,632 ( 1.22) 73,507,201,037 ( 1.22)
branches 14,455,124,835 ( 756.063) 14,455,184,779 ( 755.281) 14,378,599,509 ( 758.546)
branch-misses 69,801,336 ( 0.48%) 80,225,529 ( 0.55%) 72,044,726 ( 0.50%)
jobs2
stalled-cycles-frontend 49,912,741,782 ( 46.11%) 50,101,189,290 ( 45.95%) 32,874,195,633 ( 35.11%)
stalled-cycles-backend 27,080,366,230 ( 25.02%) 27,949,970,232 ( 25.63%) 16,461,222,706 ( 17.58%)
instructions 122,831,629,690 ( 1.13) 122,919,846,419 ( 1.13) 121,924,786,775 ( 1.30)
branches 23,725,889,239 ( 692.663) 23,733,547,140 ( 688.062) 23,553,950,311 ( 794.794)
branch-misses 90,733,041 ( 0.38%) 96,320,895 ( 0.41%) 84,561,092 ( 0.36%)
jobs3
stalled-cycles-frontend 66,437,834,608 ( 45.58%) 63,534,923,344 ( 43.69%) 42,101,478,505 ( 33.19%)
stalled-cycles-backend 34,940,799,661 ( 23.97%) 34,774,043,148 ( 23.91%) 21,163,324,388 ( 16.68%)
instructions 171,692,121,862 ( 1.18) 171,775,373,044 ( 1.18) 170,353,542,261 ( 1.34)
branches 32,968,962,622 ( 628.723) 32,987,739,894 ( 630.512) 32,729,463,918 ( 717.027)
branch-misses 111,522,732 ( 0.34%) 110,472,894 ( 0.33%) 99,791,291 ( 0.30%)
jobs4
stalled-cycles-frontend 98,741,701,675 ( 49.72%) 94,797,349,965 ( 47.59%) 54,535,655,381 ( 33.53%)
stalled-cycles-backend 54,642,609,615 ( 27.51%) 55,233,554,408 ( 27.73%) 27,882,323,541 ( 17.14%)
instructions 220,884,807,851 ( 1.11) 220,930,887,273 ( 1.11) 218,926,845,851 ( 1.35)
branches 42,354,518,180 ( 592.105) 42,362,770,587 ( 590.452) 41,955,552,870 ( 716.154)
branch-misses 138,093,449 ( 0.33%) 131,295,286 ( 0.31%) 121,794,771 ( 0.29%)
jobs5
stalled-cycles-frontend 116,219,747,212 ( 48.14%) 110,310,397,012 ( 46.29%) 66,373,082,723 ( 33.70%)
stalled-cycles-backend 66,325,434,776 ( 27.48%) 64,157,087,914 ( 26.92%) 32,999,097,299 ( 16.76%)
instructions 270,615,008,466 ( 1.12) 270,546,409,525 ( 1.14) 268,439,910,948 ( 1.36)
branches 51,834,046,557 ( 599.108) 51,811,867,722 ( 608.883) 51,412,576,077 ( 729.213)
branch-misses 158,197,086 ( 0.31%) 142,639,805 ( 0.28%) 133,425,455 ( 0.26%)
jobs6
stalled-cycles-frontend 138,009,414,492 ( 48.23%) 139,063,571,254 ( 48.80%) 75,278,568,278 ( 32.80%)
stalled-cycles-backend 79,211,949,650 ( 27.68%) 79,077,241,028 ( 27.75%) 37,735,797,899 ( 16.44%)
instructions 319,763,993,731 ( 1.12) 319,937,782,834 ( 1.12) 316,663,600,784 ( 1.38)
branches 61,219,433,294 ( 595.056) 61,250,355,540 ( 598.215) 60,523,446,617 ( 733.706)
branch-misses 169,257,123 ( 0.28%) 154,898,028 ( 0.25%) 141,180,587 ( 0.23%)
jobs7
stalled-cycles-frontend 162,974,812,119 ( 49.20%) 159,290,061,987 ( 48.43%) 88,046,641,169 ( 33.21%)
stalled-cycles-backend 92,223,151,661 ( 27.84%) 91,667,904,406 ( 27.87%) 44,068,454,971 ( 16.62%)
instructions 369,516,432,430 ( 1.12) 369,361,799,063 ( 1.12) 365,290,380,661 ( 1.38)
branches 70,795,673,950 ( 594.220) 70,743,136,124 ( 597.876) 69,803,996,038 ( 732.822)
branch-misses 181,708,327 ( 0.26%) 165,767,821 ( 0.23%) 150,109,797 ( 0.22%)
jobs8
stalled-cycles-frontend 185,000,017,027 ( 49.30%) 182,334,345,473 ( 48.37%) 99,980,147,041 ( 33.26%)
stalled-cycles-backend 105,753,516,186 ( 28.18%) 107,937,830,322 ( 28.63%) 51,404,177,181 ( 17.10%)
instructions 418,153,161,055 ( 1.11) 418,308,565,828 ( 1.11) 413,653,475,581 ( 1.38)
branches 80,035,882,398 ( 592.296) 80,063,204,510 ( 589.843) 79,024,105,589 ( 730.530)
branch-misses 199,764,528 ( 0.25%) 177,936,926 ( 0.22%) 160,525,449 ( 0.20%)
jobs9
stalled-cycles-frontend 210,941,799,094 ( 49.63%) 204,714,679,254 ( 48.55%) 114,251,113,756 ( 33.96%)
stalled-cycles-backend 122,640,849,067 ( 28.85%) 122,188,553,256 ( 28.98%) 58,360,041,127 ( 17.35%)
instructions 468,151,025,415 ( 1.10) 467,354,869,323 ( 1.11) 462,665,165,216 ( 1.38)
branches 89,657,067,510 ( 585.628) 89,411,550,407 ( 588.990) 88,360,523,943 ( 730.151)
branch-misses 218,292,301 ( 0.24%) 191,701,247 ( 0.21%) 178,535,678 ( 0.20%)
jobs10
stalled-cycles-frontend 233,595,958,008 ( 49.81%) 227,540,615,689 ( 49.11%) 160,341,979,938 ( 43.07%)
stalled-cycles-backend 136,153,676,021 ( 29.03%) 133,635,240,742 ( 28.84%) 65,909,135,465 ( 17.70%)
instructions 517,001,168,497 ( 1.10) 516,210,976,158 ( 1.11) 511,374,038,613 ( 1.37)
branches 98,911,641,329 ( 585.796) 98,700,069,712 ( 591.583) 97,646,761,028 ( 728.712)
branch-misses 232,341,823 ( 0.23%) 199,256,308 ( 0.20%) 183,135,268 ( 0.19%)

per-cpu streams tend to cause significantly less stalled cycles; execute
less branches and hit less branch-misses.

perf stat reported execution time

4 streams 8 streams per-cpu
====================================================================
jobs1
seconds elapsed 20.909073870 20.875670495 20.817838540
jobs2
seconds elapsed 18.529488399 18.720566469 16.356103108
jobs3
seconds elapsed 18.991159531 18.991340812 16.766216066
jobs4
seconds elapsed 19.560643828 19.551323547 16.246621715
jobs5
seconds elapsed 24.746498464 25.221646740 20.696112444
jobs6
seconds elapsed 28.258181828 28.289765505 22.885688857
jobs7
seconds elapsed 32.632490241 31.909125381 26.272753738
jobs8
seconds elapsed 35.651403851 36.027596308 29.108024711
jobs9
seconds elapsed 40.569362365 40.024227989 32.898204012
jobs10
seconds elapsed 44.673112304 43.874898137 35.632952191

Please see
Link: http://marc.info/?l=linux-kernel&m=146166970727530
Link: http://marc.info/?l=linux-kernel&m=146174716719650
for more test results (under low memory conditions).

Signed-off-by: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
Suggested-by: Minchan Kim <minchan@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

zram: pass gfp from zcomp frontend to backend

Each zcomp backend uses own gfp flag but it's pointless because the
context they could be called is driven by upper layer(ie, zcomp
frontend). As well, zcomp frondend could call them in different
context. One context(ie, zram init part) is it should be better to make
sure successful allocation other context(ie, further stream allocation
part for accelarating I/O speed) is just optional so let's pass gfp down
from driver (ie, zcomp frontend) like normal MM convention.

[sergey.senozhatsky@gmail.com: add missing __vmalloc zero and highmem gfps]
Signed-off-by: Minchan Kim <minchan@kernel.org>
Signed-off-by: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

zram/zcomp: use GFP_NOIO to allocate streams

We can end up allocating a new compression stream with GFP_KERNEL from
within the IO path, which may result is nested (recursive) IO
operations. That can introduce problems if the IO path in question is a
reclaimer, holding some locks that will deadlock nested IOs.

Allocate streams and working memory using GFP_NOIO flag, forbidding
recursive IO and FS operations.

An example:

inconsistent {IN-RECLAIM_FS-W} -> {RECLAIM_FS-ON-W} usage.
git/20158 [HC0[0]:SC0[0]:HE1:SE1] takes:
(jbd2_handle){+.+.?.}, at: start_this_handle+0x4ca/0x555
{IN-RECLAIM_FS-W} state was registered at:
__lock_acquire+0x8da/0x117b
lock_acquire+0x10c/0x1a7
start_this_handle+0x52d/0x555
jbd2__journal_start+0xb4/0x237
__ext4_journal_start_sb+0x108/0x17e
ext4_dirty_inode+0x32/0x61
__mark_inode_dirty+0x16b/0x60c
iput+0x11e/0x274
__dentry_kill+0x148/0x1b8
shrink_dentry_list+0x274/0x44a
prune_dcache_sb+0x4a/0x55
super_cache_scan+0xfc/0x176
shrink_slab.part.14.constprop.25+0x2a2/0x4d3
shrink_zone+0x74/0x140
kswapd+0x6b7/0x930
kthread+0x107/0x10f
ret_from_fork+0x3f/0x70
irq event stamp: 138297
hardirqs last enabled at (138297): debug_check_no_locks_freed+0x113/0x12f
hardirqs last disabled at (138296): debug_check_no_locks_freed+0x33/0x12f
softirqs last enabled at (137818): __do_softirq+0x2d3/0x3e9
softirqs last disabled at (137813): irq_exit+0x41/0x95

other info that might help us debug this:
Possible unsafe locking scenario:
CPU0
----
lock(jbd2_handle);
<Interrupt>
lock(jbd2_handle);

*** DEADLOCK ***
5 locks held by git/20158:
#0: (sb_writers#7){.+.+.+}, at: [<ffffffff81155411>] mnt_want_write+0x24/0x4b
#1: (&type->i_mutex_dir_key#2/1){+.+.+.}, at: [<ffffffff81145087>] lock_rename+0xd9/0xe3
#2: (&sb->s_type->i_mutex_key#11){+.+.+.}, at: [<ffffffff8114f8e2>] lock_two_nondirectories+0x3f/0x6b
#3: (&sb->s_type->i_mutex_key#11/4){+.+.+.}, at: [<ffffffff8114f909>] lock_two_nondirectories+0x66/0x6b
#4: (jbd2_handle){+.+.?.}, at: [<ffffffff811e31db>] start_this_handle+0x4ca/0x555

stack backtrace:
CPU: 2 PID: 20158 Comm: git Not tainted 4.1.0-rc7-next-20150615-dbg-00016-g8bdf555-dirty #211
Call Trace:
dump_stack+0x4c/0x6e
mark_lock+0x384/0x56d
mark_held_locks+0x5f/0x76
lockdep_trace_alloc+0xb2/0xb5
kmem_cache_alloc_trace+0x32/0x1e2
zcomp_strm_alloc+0x25/0x73 [zram]
zcomp_strm_multi_find+0xe7/0x173 [zram]
zcomp_strm_find+0xc/0xe [zram]
zram_bvec_rw+0x2ca/0x7e0 [zram]
zram_make_request+0x1fa/0x301 [zram]
generic_make_request+0x9c/0xdb
submit_bio+0xf7/0x120
ext4_io_submit+0x2e/0x43
ext4_bio_write_page+0x1b7/0x300
mpage_submit_page+0x60/0x77
mpage_map_and_submit_buffers+0x10f/0x21d
ext4_writepages+0xc8c/0xe1b
do_writepages+0x23/0x2c
__filemap_fdatawrite_range+0x84/0x8b
filemap_flush+0x1c/0x1e
ext4_alloc_da_blocks+0xb8/0x117
ext4_rename+0x132/0x6dc
? mark_held_locks+0x5f/0x76
ext4_rename2+0x29/0x2b
vfs_rename+0x540/0x636
SyS_renameat2+0x359/0x44d
SyS_rename+0x1e/0x20
entry_SYSCALL_64_fastpath+0x12/0x6f

[minchan@kernel.org: add stable mark]
Signed-off-by: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
Acked-by: Minchan Kim <minchan@kernel.org>
Cc: Kyeongdon Kim <kyeongdon.kim@lge.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

zram: fix possible use after free in zcomp_create()

zcomp_create() verifies the success of zcomp_strm_{multi,single}_create()
through comp->stream, which can potentially be pointing to memory that
was freed if these functions returned an error.

While at it, replace a 'ERR_PTR(-ENOMEM)' by a more generic
'ERR_PTR(error)' as in the future zcomp_strm_{multi,siggle}_create()
could return other error codes. Function documentation updated
accordingly.

Fixes: beca3ec71fe5 ("zram: add multi stream functionality")
Signed-off-by: Luis Henriques <luis.henriques@canonical.com>
Acked-by: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
Acked-by: Minchan Kim <minchan@kernel.org>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

zram: check comp algorithm availability earlier

Improvement idea by Marcin Jabrzyk.

comp_algorithm_store() silently accepts any supplied algorithm name,
because zram performs algorithm availability check later, during the
device configuration phase in disksize_store() and emits the following
error:

"zram: Cannot initialise %s compressing backend"

this error line is somewhat generic and, besides, can indicate a failed
attempt to allocate compression backend's working buffers.

add algorithm availability check to comp_algorithm_store():

echo lzz > /sys/block/zram0/comp_algorithm
-bash: echo: write error: Invalid argument

Signed-off-by: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
Reported-by: Marcin Jabrzyk <m.jabrzyk@samsung.com>
Acked-by: Minchan Kim <minchan@kernel.org>
Cc: Nitin Gupta <ngupta@vflare.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

zram: cut trailing newline in algorithm name

Supplied sysfs values sometimes contain new-line symbols (echo vs. echo
-n), which we also copy as a compression algorithm name. it works fine
when we lookup for compression algorithm, because we use sysfs_streq()
which takes care of new line symbols. however, it doesn't look nice when
we print compression algorithm name if zcomp_create() failed:

zram: Cannot initialise LXZ
compressing backend

cut trailing new-line, so the error string will look like

zram: Cannot initialise LXZ compressing backend

we also now can replace sysfs_streq() in zcomp_available_show() with
strcmp().

Signed-off-by: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
Cc: Minchan Kim <minchan@kernel.org>
Cc: Nitin Gupta <ngupta@vflare.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

zram: use scnprintf() in attrs show() methods

sysfs.txt documentation lists the following requirements:

- The buffer will always be PAGE_SIZE bytes in length. On i386, this
is 4096.

- show() methods should return the number of bytes printed into the
buffer. This is the return value of scnprintf().

- show() should always use scnprintf().

Use scnprintf() in show() functions.

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>

zram: propagate error to user

When we initialized zcomp with single, we couldn't change
max_comp_streams without zram reset but current interface doesn't show
any error to user and even it changes max_comp_streams's value without
any effect so it would make user very confusing.

This patch prevents max_comp_streams's change when zcomp was initialized
as single zcomp and emit the error to user(ex, echo).

[akpm@linux-foundation.org: don't return with the lock held, per Sergey]
[fengguang.wu@intel.com: fix coccinelle warnings]
Signed-off-by: Minchan Kim <minchan@kernel.org>
Cc: Nitin Gupta <ngupta@vflare.org>
Cc: Jerome Marchand <jmarchan@redhat.com>
Acked-by: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
Signed-off-by: Fengguang Wu <fengguang.wu@intel.com>
Cc: Stephen Rothwell <sfr@canb.auug.org.au>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

zram: return error-valued pointer from zcomp_create()

Instead of returning just NULL, return ERR_PTR from zcomp_create() if
compressing backend creation has failed. ERR_PTR(-EINVAL) for unsupported
compression algorithm request, ERR_PTR(-ENOMEM) for allocation (zcomp or
compression stream) error.

Perform IS_ERR() check of returned from zcomp_create() value in
disksize_store() and set return code to PTR_ERR().

Change suggested by Jerome Marchand.

[akpm@linux-foundation.org: clean up error recovery flow]
Signed-off-by: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
Reported-by: Jerome Marchand <jmarchan@redhat.com>
Cc: Minchan Kim <minchan@kernel.org>
Cc: Nitin Gupta <ngupta@vflare.org>
Cc: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

zram: add lz4 algorithm backend

Introduce LZ4 compression backend and make it available for selection.
LZ4 support is optional and requires user to set ZRAM_LZ4_COMPRESS config
option. The default compression backend is LZO.

TEST

(x86_64, core i5, 2 cores + 2 hyperthreading, zram disk size 1G,
ext4 file system, 3 compression streams)

iozone -t 3 -R -r 16K -s 60M -I +Z

Test LZO LZ4
----------------------------------------------
Initial write 1642744.62 1317005.09
Rewrite 2498980.88 1800645.16
Read 3957026.38 5877043.75
Re-read 3950997.38 5861847.00
Reverse Read 2937114.56 5047384.00
Stride read 2948163.19 4929587.38
Random read 3292692.69 4880793.62
Mixed workload 1545602.62 3502940.38
Random write 2448039.75 1758786.25
Pwrite 1670051.03 1338329.69
Pread 2530682.00 5097177.62
Fwrite 3232085.62 3275942.56
Fread 6306880.25 6645271.12

So on my system LZ4 is slower in write-only tests, while it performs
better in read-only and mixed (reads + writes) tests.

Official LZ4 benchmarks available here http://code.google.com/p/lz4/
(linux kernel uses revision r90).

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>

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 <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>

zram: add set_max_streams knob

This patch allows to change max_comp_streams on initialised zcomp.

Introduce zcomp set_max_streams() knob, zcomp_strm_multi_set_max_streams()
and zcomp_strm_single_set_max_streams() callbacks to change streams limit
for zcomp_strm_multi and zcomp_strm_single, accordingly. set_max_streams
for single steam zcomp does nothing.

If user has lowered the limit, then zcomp_strm_multi_set_max_streams()
attempts to immediately free extra streams (as much as it can, depending
on idle streams availability).

Note, this patch does not allow to change stream 'policy' from single to
multi stream (or vice versa) on already initialised compression backend.

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>

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>

zram: factor out single stream compression

This is preparation patch to add multi stream support to zcomp.

Introduce struct zcomp_strm_single and a set of functions to manage
zcomp_strm stream access. zcomp_strm_single implements single compession
stream, same way as current zcomp implementation. This moves zcomp_strm
stream control and locking from zcomp, so compressing backend zcomp is not
aware of required locking.

Single and multi streams require different locking schemes. Minchan Kim
reported that spinlock-based locking scheme (which is used in multi stream
implementation) has demonstrated a severe perfomance regression for single
compression stream case, comparing to mutex-based. see
https://lkml.org/lkml/2014/2/18/16

The following set of functions added:
- zcomp_strm_single_find()/zcomp_strm_single_release()
find and release a compression stream, implement required locking
- zcomp_strm_single_create()/zcomp_strm_single_destroy()
create and destroy zcomp_strm_single

New ->strm_find() and ->strm_release() callbacks added to zcomp, which are
set to zcomp_strm_single_find() and zcomp_strm_single_release() during
initialisation. Instead of direct locking and zcomp_strm access from
zcomp_strm_find() and zcomp_strm_release(), zcomp now calls ->strm_find()
and ->strm_release() correspondingly.

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>

zram: introduce compressing backend abstraction

ZRAM performs direct LZO compression algorithm calls, making it the one
and only option. While LZO is generally performs well, LZ4 algorithm
tends to have a faster decompression (see http://code.google.com/p/lz4/
for full report)

Name Ratio C.speed D.speed
MB/s MB/s
LZ4 (r101) 2.084 422 1820
LZO 2.06 2.106 414 600

Thus, users who have mostly read (decompress) usage scenarious or mixed
workflow (writes with relatively high read ops number) will benefit from
using LZ4 compression backend.

Introduce compressing backend abstraction zcomp in order to support
multiple compression algorithms with the following set of operations:

.create
.destroy
.compress
.decompress

Schematically zram write() usually contains the following steps:
0) preparation (decompression of partioal IO, etc.)
1) lock buffer_lock mutex (protects meta compress buffers)
2) compress (using meta compress buffers)
3) alloc and map zs_pool object
4) copy compressed data (from meta compress buffers) to object allocated by 3)
5) free previous pool page, assign a new one
6) unlock buffer_lock mutex

As we can see, compressing buffers must remain untouched from 1) to 4),
because, otherwise, concurrent write() can overwrite data. At the same
time, zram_meta must be aware of a) specific compression algorithm memory
requirements and b) necessary locking to protect compression buffers. To
remove requirement a) new struct zcomp_strm introduced, which contains a
compress/decompress `buffer' and compression algorithm `private' part.
While struct zcomp implements zcomp_strm stream handling and locking and
removes requirement b) from zram meta. zcomp ->create() and ->destroy(),
respectively, allocate and deallocate algorithm specific zcomp_strm
`private' part.

Every zcomp has zcomp stream and mutex to protect its compression stream.
Stream usage semantics remains the same -- only one write can hold stream
lock and use its buffers. zcomp_strm_find() turns caller into exclusive
user of a stream (holding stream mutex until zram release stream), and
zcomp_strm_release() makes zcomp stream available (unlock the stream
mutex). Hence no concurrent write (compression) operations possible at
the moment.

iozone -t 3 -R -r 16K -s 60M -I +Z

test base patched
--------------------------------------------------
Initial write 597992.91 591660.58
Rewrite 609674.34 616054.97
Read 2404771.75 2452909.12
Re-read 2459216.81 2470074.44
Reverse Read 1652769.66 1589128.66
Stride read 2202441.81 2202173.31
Random read 2236311.47 2276565.31
Mixed workload 1423760.41 1709760.06
Random write 579584.08 615933.86
Pwrite 597550.02 594933.70
Pread 1703672.53 1718126.72
Fwrite 1330497.06 1461054.00
Fread 3922851.00 3957242.62

Usage examples:

comp = zcomp_create(NAME) /* NAME e.g. "lzo" */

which initialises compressing backend if requested algorithm is supported.

Compress:
zstrm = zcomp_strm_find(comp)
zcomp_compress(comp, zstrm, src, &dst_len)
[..] /* copy compressed data */
zcomp_strm_release(comp, zstrm)

Decompress:
zcomp_decompress(comp, src, src_len, dst);

Free compessing backend and its zcomp stream:
zcomp_destroy(comp)

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>