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Author SHA1 Message Date
Weijie Yang d2d5e762c8 zram: replace global tb_lock with fine grain lock 
Currently, we use a rwlock tb_lock to protect concurrent access to the
whole zram meta table.  However, according to the actual access model,
there is only a small chance for upper user to access the same
table[index], so the current lock granularity is too big.

The idea of optimization is to change the lock granularity from whole
meta table to per table entry (table -> table[index]), so that we can
protect concurrent access to the same table[index], meanwhile allow the
maximum concurrency.

With this in mind, several kinds of locks which could be used as a
per-entry lock were tested and compared:

Test environment:
x86-64 Intel Core2 Q8400, system memory 4GB, Ubuntu 12.04,
kernel v3.15.0-rc3 as base, zram with 4 max_comp_streams LZO.

iozone test:
iozone -t 4 -R -r 16K -s 200M -I +Z
(1GB zram with ext4 filesystem, take the average of 10 tests, KB/s)

      Test       base      CAS    spinlock    rwlock   bit_spinlock
-------------------------------------------------------------------
 Initial write  1381094   1425435   1422860   1423075   1421521
       Rewrite  1529479   1641199   1668762   1672855   1654910
          Read  8468009  11324979  11305569  11117273  10997202
       Re-read  8467476  11260914  11248059  11145336  10906486
  Reverse Read  6821393   8106334   8282174   8279195   8109186
   Stride read  7191093   8994306   9153982   8961224   9004434
   Random read  7156353   8957932   9167098   8980465   8940476
Mixed workload  4172747   5680814   5927825   5489578   5972253
  Random write  1483044   1605588   1594329   1600453   1596010
        Pwrite  1276644   1303108   1311612   1314228   1300960
         Pread  4324337   4632869   4618386   4457870   4500166

To enhance the possibility of access the same table[index] concurrently,
set zram a small disksize(10MB) and let threads run with large loop
count.

fio test:
fio --bs=32k --randrepeat=1 --randseed=100 --refill_buffers
--scramble_buffers=1 --direct=1 --loops=3000 --numjobs=4
--filename=/dev/zram0 --name=seq-write --rw=write --stonewall
--name=seq-read --rw=read --stonewall --name=seq-readwrite
--rw=rw --stonewall --name=rand-readwrite --rw=randrw --stonewall
(10MB zram raw block device, take the average of 10 tests, KB/s)

    Test     base     CAS    spinlock    rwlock  bit_spinlock
-------------------------------------------------------------
seq-write   933789   999357   1003298    995961   1001958
 seq-read  5634130  6577930   6380861   6243912   6230006
   seq-rw  1405687  1638117   1640256   1633903   1634459
  rand-rw  1386119  1614664   1617211   1609267   1612471

All the optimization methods show a higher performance than the base,
however, it is hard to say which method is the most appropriate.

On the other hand, zram is mostly used on small embedded system, so we
don't want to increase any memory footprint.

This patch pick the bit_spinlock method, pack object size and page_flag
into an unsigned long table.value, so as to not increase any memory
overhead on both 32-bit and 64-bit system.

On the third hand, even though different kinds of locks have different
performances, we can ignore this difference, because: if zram is used as
zram swapfile, the swap subsystem can prevent concurrent access to the
same swapslot; if zram is used as zram-blk for set up filesystem on it,
the upper filesystem and the page cache also prevent concurrent access
of the same block mostly.  So we can ignore the different performances
among locks.

Acked-by: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
Reviewed-by: Davidlohr Bueso <davidlohr@hp.com>
Signed-off-by: Weijie Yang <weijie.yang@samsung.com>
Signed-off-by: Minchan Kim <minchan@kernel.org>
Cc: Jerome Marchand <jmarchan@redhat.com>
Cc: Nitin Gupta <ngupta@vflare.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
 2014-08-06 18:01:23 -07:00
Sergey Senozhatsky a830eff749 zram: remove unused SECTOR_SIZE define 
Drop SECTOR_SIZE define, because it's not used.

Signed-off-by: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
Cc: Minchan Kim <minchan@kernel.org>
Cc: Nitin Gupta <ngupta@vflare.org>
Cc: Weijie Yang <weijie.yang@samsung.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
 2014-08-06 18:01:22 -07:00
Sergey Senozhatsky cb8f2eec3c zram: rename struct `table' to `zram_table_entry' 
Andrew Morton has recently noted that `struct table' actually represents
table entry and, thus, should be renamed.  Rename to `zram_table_entry'.

Signed-off-by: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
Cc: Minchan Kim <minchan@kernel.org>
Cc: Nitin Gupta <ngupta@vflare.org>
Cc: Weijie Yang <weijie.yang@samsung.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
 2014-08-06 18:01:22 -07:00
Sergey Senozhatsky e46b8a030d 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>
 2014-04-07 16:36:01 -07:00
Sergey Senozhatsky beca3ec71f zram: add multi stream functionality 
Existing zram (zcomp) implementation has only one compression stream
(buffer and algorithm private part), so in order to prevent data
corruption only one write (compress operation) can use this compression
stream, forcing all concurrent write operations to wait for stream lock
to be released.  This patch changes zcomp to keep a compression streams
list of user-defined size (via sysfs device attr).  Each write operation
still exclusively holds compression stream, the difference is that we
can have N write operations (depending on size of streams list)
executing in parallel.  See TEST section later in commit message for
performance data.

Introduce struct zcomp_strm_multi and a set of functions to manage
zcomp_strm stream access.  zcomp_strm_multi has a list of idle
zcomp_strm structs, spinlock to protect idle list and wait queue, making
it possible to perform parallel compressions.

The following set of functions added:
- zcomp_strm_multi_find()/zcomp_strm_multi_release()
  find and release a compression stream, implement required locking
- zcomp_strm_multi_create()/zcomp_strm_multi_destroy()
  create and destroy zcomp_strm_multi

zcomp ->strm_find() and ->strm_release() callbacks are set during
initialisation to zcomp_strm_multi_find()/zcomp_strm_multi_release()
correspondingly.

Each time zcomp issues a zcomp_strm_multi_find() call, the following set
of operations performed:

- spin lock strm_lock
- if idle list is not empty, remove zcomp_strm from idle list, spin
  unlock and return zcomp stream pointer to caller
- if idle list is empty, current adds itself to wait queue. it will be
  awaken by zcomp_strm_multi_release() caller.

zcomp_strm_multi_release():
- spin lock strm_lock
- add zcomp stream to idle list
- spin unlock, wake up sleeper

Minchan Kim reported that spinlock-based locking scheme has demonstrated
a severe perfomance regression for single compression stream case,
comparing to mutex-based (see https://lkml.org/lkml/2014/2/18/16)

base                      spinlock                    mutex

==Initial write           ==Initial write             ==Initial  write
records:  5               records:  5                 records:   5
avg:      1642424.35      avg:      699610.40         avg:       1655583.71
std:      39890.95(2.43%) std:      232014.19(33.16%) std:       52293.96
max:      1690170.94      max:      1163473.45        max:       1697164.75
min:      1568669.52      min:      573429.88         min:       1553410.23
==Rewrite                 ==Rewrite                   ==Rewrite
records:  5               records:  5                 records:   5
avg:      1611775.39      avg:      501406.64         avg:       1684419.11
std:      17144.58(1.06%) std:      15354.41(3.06%)   std:       18367.42
max:      1641800.95      max:      531356.78         max:       1706445.84
min:      1593515.27      min:      488817.78         min:       1655335.73

When only one compression stream available, mutex with spin on owner
tends to perform much better than frequent wait_event()/wake_up().  This
is why single stream implemented as a special case with mutex locking.

Introduce and document zram device attribute max_comp_streams.  This
attr shows and stores current zcomp's max number of zcomp streams
(max_strm).  Extend zcomp's zcomp_create() with `max_strm' parameter.
`max_strm' limits the number of zcomp_strm structs in compression
backend's idle list (max_comp_streams).

max_comp_streams used during initialisation as follows:
-- passing to zcomp_create() max_strm equals to 1 will initialise zcomp
using single compression stream zcomp_strm_single (mutex-based locking).
-- passing to zcomp_create() max_strm greater than 1 will initialise zcomp
using multi compression stream zcomp_strm_multi (spinlock-based locking).

default max_comp_streams value is 1, meaning that zram with single stream
will be initialised.

Later patch will introduce configuration knob to change max_comp_streams
on already initialised and used zcomp.

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

       test           base       1 strm (mutex)     3 strm (spinlock)
-----------------------------------------------------------------------
 Initial write      589286.78       583518.39          718011.05
       Rewrite      604837.97       596776.38         1515125.72
  Random write      584120.11       595714.58         1388850.25
        Pwrite      535731.17       541117.38          739295.27
        Fwrite     1418083.88      1478612.72         1484927.06

Usage example:
set max_comp_streams to 4
        echo 4 > /sys/block/zram0/max_comp_streams

show current max_comp_streams (default value is 1).
        cat /sys/block/zram0/max_comp_streams

Signed-off-by: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
Acked-by: Minchan Kim <minchan@kernel.org>
Cc: Jerome Marchand <jmarchan@redhat.com>
Cc: Nitin Gupta <ngupta@vflare.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
 2014-04-07 16:36:01 -07:00
Sergey Senozhatsky b7ca232ee7 zram: use zcomp compressing backends 
Do not perform direct LZO compress/decompress calls, initialise
and use zcomp LZO backend (single compression stream) instead.

[akpm@linux-foundation.org: resolve conflicts with zram-delete-zram_init_device-fix.patch]
Signed-off-by: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
Acked-by: Minchan Kim <minchan@kernel.org>
Cc: Jerome Marchand <jmarchan@redhat.com>
Cc: Nitin Gupta <ngupta@vflare.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
 2014-04-07 16:36:01 -07:00
Sergey Senozhatsky 59fc86a492 zram: drop not used table `count' member 
struct table `count' member is not used.

Signed-off-by: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
Cc: Minchan Kim <minchan@kernel.org>
Acked-by: Jerome Marchand <jmarchan@redhat.com>
Cc: Nitin Gupta <ngupta@vflare.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
 2014-04-07 16:36:00 -07:00
Sergey Senozhatsky 90a7806ea9 zram: use atomic64_t for all zram stats 
This is a preparation patch for stats code duplication removal.

1) use atomic64_t for `pages_zero' and `pages_stored' zram stats.

2) `compr_size' and `pages_zero' struct zram_stats members did not
   follow the existing device attr naming scheme: zram_stats.ATTR has
   ATTR_show() function.  rename them:

   -- compr_size -> compr_data_size
   -- pages_zero -> zero_pages

Minchan Kim's note:
 If we really have trouble with atomic stat operation, we could
 change it with percpu_counter so that it could solve atomic overhead and
 unnecessary memory space by introducing unsigned long instead of 64bit
 atomic_t.

Signed-off-by: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
Acked-by: Minchan Kim <minchan@kernel.org>
Acked-by: Jerome Marchand <jmarchan@redhat.com>
Cc: Nitin Gupta <ngupta@vflare.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
 2014-04-07 16:35:59 -07:00
Sergey Senozhatsky b7cccf8b40 zram: remove good and bad compress stats 
Remove `good' and `bad' compressed sub-requests stats.  RW request may
cause a number of RW sub-requests.  zram used to account `good' compressed
sub-queries (with compressed size less than 50% of original size), `bad'
compressed sub-queries (with compressed size greater that 75% of original
size), leaving sub-requests with compression size between 50% and 75% of
original size not accounted and not reported.  zram already accounts each
sub-request's compression size so we can calculate real device compression
ratio.

Signed-off-by: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
Acked-by: Minchan Kim <minchan@kernel.org>
Acked-by: Jerome Marchand <jmarchan@redhat.com>
Cc: Nitin Gupta <ngupta@vflare.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
 2014-04-07 16:35:59 -07:00
Sergey Senozhatsky be2d1d56c8 zram: drop `init_done' struct zram member 
Introduce init_done() helper function which allows us to drop `init_done'
struct zram member.  init_done() uses the fact that ->init_done == 1
equals to ->meta != NULL.

Signed-off-by: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
Acked-by: Minchan Kim <minchan@kernel.org>
Acked-by: Jerome Marchand <jmarchan@redhat.com>
Cc: Nitin Gupta <ngupta@vflare.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
 2014-04-07 16:35:59 -07:00
Minchan Kim e46e33152e zram: remove zram->lock in read path and change it with mutex 
Finally, we separated zram->lock dependency from 32bit stat/ table
handling so there is no reason to use rw_semaphore between read and
write path so this patch removes the lock from read path totally and
changes rw_semaphore with mutex.  So, we could do

old:

  read-read: OK
  read-write: NO
  write-write: NO

Now:

  read-read: OK
  read-write: OK
  write-write: NO

The below data proves mixed workload performs well 11 times and there is
also enhance on write-write path because current rw-semaphore doesn't
support SPIN_ON_OWNER.  It's side effect but anyway good thing for us.

Write-related tests perform better (from 61% to 1058%) but read path has
good/bad(from -2.22% to 1.45%) but they are all marginal within stddev.

  CPU 12
  iozone -t -T -l 12 -u 12 -r 16K -s 60M -I +Z -V 0

  ==Initial write                ==Initial write
  records: 10                    records: 10
  avg:  516189.16                avg:  839907.96
  std:   22486.53 (4.36%)        std:   47902.17 (5.70%)
  max:  546970.60                max:  909910.35
  min:  481131.54                min:  751148.38
  ==Rewrite                      ==Rewrite
  records: 10                    records: 10
  avg:  509527.98                avg: 1050156.37
  std:   45799.94 (8.99%)        std:   40695.44 (3.88%)
  max:  611574.27                max: 1111929.26
  min:  443679.95                min:  980409.62
  ==Read                         ==Read
  records: 10                    records: 10
  avg: 4408624.17                avg: 4472546.76
  std:  281152.61 (6.38%)        std:  163662.78 (3.66%)
  max: 4867888.66                max: 4727351.03
  min: 4058347.69                min: 4126520.88
  ==Re-read                      ==Re-read
  records: 10                    records: 10
  avg: 4462147.53                avg: 4363257.75
  std:  283546.11 (6.35%)        std:  247292.63 (5.67%)
  max: 4912894.44                max: 4677241.75
  min: 4131386.50                min: 4035235.84
  ==Reverse Read                 ==Reverse Read
  records: 10                    records: 10
  avg: 4565865.97                avg: 4485818.08
  std:  313395.63 (6.86%)        std:  248470.10 (5.54%)
  max: 5232749.16                max: 4789749.94
  min: 4185809.62                min: 3963081.34
  ==Stride read                  ==Stride read
  records: 10                    records: 10
  avg: 4515981.80                avg: 4418806.01
  std:  211192.32 (4.68%)        std:  212837.97 (4.82%)
  max: 4889287.28                max: 4686967.22
  min: 4210362.00                min: 4083041.84
  ==Random read                  ==Random read
  records: 10                    records: 10
  avg: 4410525.23                avg: 4387093.18
  std:  236693.22 (5.37%)        std:  235285.23 (5.36%)
  max: 4713698.47                max: 4669760.62
  min: 4057163.62                min: 3952002.16
  ==Mixed workload               ==Mixed workload
  records: 10                    records: 10
  avg:  243234.25                avg: 2818677.27
  std:   28505.07 (11.72%)       std:  195569.70 (6.94%)
  max:  288905.23                max: 3126478.11
  min:  212473.16                min: 2484150.69
  ==Random write                 ==Random write
  records: 10                    records: 10
  avg:  555887.07                avg: 1053057.79
  std:   70841.98 (12.74%)       std:   35195.36 (3.34%)
  max:  683188.28                max: 1096125.73
  min:  437299.57                min:  992481.93
  ==Pwrite                       ==Pwrite
  records: 10                    records: 10
  avg:  501745.93                avg:  810363.09
  std:   16373.54 (3.26%)        std:   19245.01 (2.37%)
  max:  518724.52                max:  833359.70
  min:  464208.73                min:  765501.87
  ==Pread                        ==Pread
  records: 10                    records: 10
  avg: 4539894.60                avg: 4457680.58
  std:  197094.66 (4.34%)        std:  188965.60 (4.24%)
  max: 4877170.38                max: 4689905.53
  min: 4226326.03                min: 4095739.72

Signed-off-by: Minchan Kim <minchan@kernel.org>
Cc: Nitin Gupta <ngupta@vflare.org>
Tested-by: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
Cc: Jerome Marchand <jmarchan@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
 2014-01-30 16:56:56 -08:00
Minchan Kim f614a9f48d zram: remove workqueue for freeing removed pending slot 
Commit a0c516cbfc ("zram: don't grab mutex in zram_slot_free_noity")
introduced free request pending code to avoid scheduling by mutex under
spinlock and it was a mess which made code lenghty and increased
overhead.

Now, we don't need zram->lock any more to free slot so this patch
reverts it and then, tb_lock should protect it.

Signed-off-by: Minchan Kim <minchan@kernel.org>
Cc: Nitin Gupta <ngupta@vflare.org>
Tested-by: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
Cc: Jerome Marchand <jmarchan@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
 2014-01-30 16:56:55 -08:00
Minchan Kim 92967471b6 zram: introduce zram->tb_lock 
Currently, the zram table is protected by zram->lock but it's rather
coarse-grained lock and it makes hard for scalibility.

Let's use own rwlock instead of depending on zram->lock.  This patch
adds new locking so obviously, it would make slow but this patch is just
prepartion for removing coarse-grained rw_semaphore(ie, zram->lock)
which is hurdle about zram scalability.

Final patch in this patchset series will remove the lock from read-path
and change rw_semaphore with mutex in write path.  With bonus, we could
drop pending slot free mess in next patch.

Signed-off-by: Minchan Kim <minchan@kernel.org>
Cc: Nitin Gupta <ngupta@vflare.org>
Tested-by: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
Cc: Jerome Marchand <jmarchan@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
 2014-01-30 16:56:55 -08:00
Minchan Kim deb0bdeb2f zram: use atomic operation for stat 
Some of fields in zram->stats are protected by zram->lock which is
rather coarse-grained so let's use atomic operation without explict
locking.

This patch is ready for removing dependency of zram->lock in read path
which is very coarse-grained rw_semaphore.  Of course, this patch adds
new atomic operation so it might make slow but my 12CPU test couldn't
spot any regression.  All gain/lose is marginal within stddev.

  iozone -t -T -l 12 -u 12 -r 16K -s 60M -I +Z -V 0

  ==Initial write                ==Initial write
  records: 50                    records: 50
  avg:  412875.17                avg:  415638.23
  std:   38543.12 (9.34%)        std:   36601.11 (8.81%)
  max:  521262.03                max:  502976.72
  min:  343263.13                min:  351389.12
  ==Rewrite                      ==Rewrite
  records: 50                    records: 50
  avg:  416640.34                avg:  397914.33
  std:   60798.92 (14.59%)       std:   46150.42 (11.60%)
  max:  543057.07                max:  522669.17
  min:  304071.67                min:  316588.77
  ==Read                         ==Read
  records: 50                    records: 50
  avg: 4147338.63                avg: 4070736.51
  std:  179333.25 (4.32%)        std:  223499.89 (5.49%)
  max: 4459295.28                max: 4539514.44
  min: 3753057.53                min: 3444686.31
  ==Re-read                      ==Re-read
  records: 50                    records: 50
  avg: 4096706.71                avg: 4117218.57
  std:  229735.04 (5.61%)        std:  171676.25 (4.17%)
  max: 4430012.09                max: 4459263.94
  min: 2987217.80                min: 3666904.28
  ==Reverse Read                 ==Reverse Read
  records: 50                    records: 50
  avg: 4062763.83                avg: 4078508.32
  std:  186208.46 (4.58%)        std:  172684.34 (4.23%)
  max: 4401358.78                max: 4424757.22
  min: 3381625.00                min: 3679359.94
  ==Stride read                  ==Stride read
  records: 50                    records: 50
  avg: 4094933.49                avg: 4082170.22
  std:  185710.52 (4.54%)        std:  196346.68 (4.81%)
  max: 4478241.25                max: 4460060.97
  min: 3732593.23                min: 3584125.78
  ==Random read                  ==Random read
  records: 50                    records: 50
  avg: 4031070.04                avg: 4074847.49
  std:  192065.51 (4.76%)        std:  206911.33 (5.08%)
  max: 4356931.16                max: 4399442.56
  min: 3481619.62                min: 3548372.44
  ==Mixed workload               ==Mixed workload
  records: 50                    records: 50
  avg:  149925.73                avg:  149675.54
  std:    7701.26 (5.14%)        std:    6902.09 (4.61%)
  max:  191301.56                max:  175162.05
  min:  133566.28                min:  137762.87
  ==Random write                 ==Random write
  records: 50                    records: 50
  avg:  404050.11                avg:  393021.47
  std:   58887.57 (14.57%)       std:   42813.70 (10.89%)
  max:  601798.09                max:  524533.43
  min:  325176.99                min:  313255.34
  ==Pwrite                       ==Pwrite
  records: 50                    records: 50
  avg:  411217.70                avg:  411237.96
  std:   43114.99 (10.48%)       std:   33136.29 (8.06%)
  max:  530766.79                max:  471899.76
  min:  320786.84                min:  317906.94
  ==Pread                        ==Pread
  records: 50                    records: 50
  avg: 4154908.65                avg: 4087121.92
  std:  151272.08 (3.64%)        std:  219505.04 (5.37%)
  max: 4459478.12                max: 4435857.38
  min: 3730512.41                min: 3101101.67

Signed-off-by: Minchan Kim <minchan@kernel.org>
Cc: Nitin Gupta <ngupta@vflare.org>
Tested-by: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
Cc: Jerome Marchand <jmarchan@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
 2014-01-30 16:56:55 -08:00
Minchan Kim 7bfb3de8a1 zram: add copyright 
Add my copyright to the zram source code which I maintain.

Signed-off-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>
 2014-01-30 16:56:55 -08:00
Minchan Kim 49061236a9 zram: remove old private project comment 
Remove the old private compcache project address so upcoming patches
should be sent to LKML because we Linux kernel community will take care.

Signed-off-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>
 2014-01-30 16:56:55 -08:00
Minchan Kim cd67e10ac6 zram: promote zram from staging 
Zram has lived in staging for a LONG LONG time and have been
fixed/improved by many contributors so code is clean and stable now.  Of
course, there are lots of product using zram in real practice.

The major TV companys have used zram as swap since two years ago and
recently our production team released android smart phone with zram
which is used as swap, too and recently Android Kitkat start to use zram
for small memory smart phone.  And there was a report Google released
their ChromeOS with zram, too and cyanogenmod have been used zram long
time ago.  And I heard some disto have used zram block device for tmpfs.
In addition, I saw many report from many other peoples.  For example,
Lubuntu start to use it.

The benefit of zram is very clear.  With my experience, one of the
benefit was to remove jitter of video application with backgroud memory
pressure.  It would be effect of efficient memory usage by compression
but more issue is whether swap is there or not in the system.  Recent
mobile platforms have used JAVA so there are many anonymous pages.  But
embedded system normally are reluctant to use eMMC or SDCard as swap
because there is wear-leveling and latency issues so if we do not use
swap, it means we can't reclaim anoymous pages and at last, we could
encounter OOM kill.  :(

Although we have real storage as swap, it was a problem, too.  Because
it sometime ends up making system very unresponsible caused by slow swap
storage performance.

Quote from Luigi on Google
 "Since Chrome OS was mentioned: the main reason why we don't use swap
  to a disk (rotating or SSD) is because it doesn't degrade gracefully
  and leads to a bad interactive experience.  Generally we prefer to
  manage RAM at a higher level, by transparently killing and restarting
  processes.  But we noticed that zram is fast enough to be competitive
  with the latter, and it lets us make more efficient use of the
  available RAM.  " and he announced.
http://www.spinics.net/lists/linux-mm/msg57717.html

Other uses case is to use zram for block device.  Zram is block device
so anyone can format the block device and mount on it so some guys on
the internet start zram as /var/tmp.
http://forums.gentoo.org/viewtopic-t-838198-start-0.html

Let's promote zram and enhance/maintain it instead of removing.

Signed-off-by: Minchan Kim <minchan@kernel.org>
Reviewed-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
Acked-by: Nitin Gupta <ngupta@vflare.org>
Acked-by: Pekka Enberg <penberg@kernel.org>
Cc: Bob Liu <bob.liu@oracle.com>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Hugh Dickins <hughd@google.com>
Cc: Jens Axboe <axboe@kernel.dk>
Cc: Luigi Semenzato <semenzato@google.com>
Cc: Mel Gorman <mgorman@suse.de>
Cc: Rik van Riel <riel@redhat.com>
Cc: Seth Jennings <sjenning@linux.vnet.ibm.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
 2014-01-30 16:56:55 -08:00