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>
Signed-off-by: Pranav Vashi <neobuddy89@gmail.com>
Signed-off-by: Joao Paulo <joaolrpaulo@gmail.com>
Signed-off-by: TomorrowLandAce <joaolrpaulo@gmail.com>
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>
Signed-off-by: Pranav Vashi <neobuddy89@gmail.com>
Signed-off-by: Joao Paulo <joaolrpaulo@gmail.com>
Signed-off-by: TomorrowLandAce <joaolrpaulo@gmail.com>
zram: fix race between reset and flushing pending work

Dan and Sergey reported that there is a racy between reset and flushing
of pending work so that it could make oops by freeing zram->meta in
reset while zram_slot_free can access zram->meta if new request is
adding during the race window.

This patch moves flush after taking init_lock so it prevents new request
so that it closes the race.

Signed-off-by: Minchan Kim <minchan@kernel.org>
Reported-by: Dan Carpenter <dan.carpenter@oracle.com>
Cc: Nitin Gupta <ngupta@vflare.org>
Cc: Jerome Marchand <jmarchan@redhat.com>
Tested-by: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Pranav Vashi <neobuddy89@gmail.com>
Signed-off-by: Joao Paulo <joaolrpaulo@gmail.com>
Signed-off-by: TomorrowLandAce <joaolrpaulo@gmail.com>
zram: delay pending free request in read path

Sergey reported we don't need to handle pending free request every I/O
so that this patch removes it in read path while we remain it in write
path.

Let's consider below example.

Swap subsystem ask to zram "A" block free by swap_slot_free_notify but
zram had been pended it without real freeing.  Swap subsystem allocates
"A" block for new data but request pended for a long time just handled
and zram blindly free new data on the "A" block.  :(

That's why we couldn't remove handle pending free request right before
zram-write.

Signed-off-by: Minchan Kim <minchan@kernel.org>
Reported-by: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
Tested-by: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
Cc: Nitin Gupta <ngupta@vflare.org>
Cc: Jerome Marchand <jmarchan@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Pranav Vashi <neobuddy89@gmail.com>
Signed-off-by: Joao Paulo <joaolrpaulo@gmail.com>
Signed-off-by: TomorrowLandAce <joaolrpaulo@gmail.com>
zram: remove unnecessary free

Commit e7400d00b76a2eb057c3c2b7b679bdb9c3c698cb ("zram: don't grab mutex in zram_slot_free_noity")
introduced pending zram slot free in zram's write path in case of
missing slot free by memory allocation failure in zram_slot_free_notify
but it is not necessary because we have already freed the slot right
before overwriting.

Signed-off-by: Minchan Kim <minchan@kernel.org>
Cc: Nitin Gupta <ngupta@vflare.org>
Cc: Jerome Marchand <jmarchan@redhat.com>
Tested-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>
Signed-off-by: Pranav Vashi <neobuddy89@gmail.com>
Signed-off-by: Joao Paulo <joaolrpaulo@gmail.com>
Signed-off-by: TomorrowLandAce <joaolrpaulo@gmail.com>
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>
Signed-off-by: Pranav Vashi <neobuddy89@gmail.com>
Signed-off-by: Joao Paulo <joaolrpaulo@gmail.com>
Signed-off-by: TomorrowLandAce <joaolrpaulo@gmail.com>
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>
Signed-off-by: Pranav Vashi <neobuddy89@gmail.com>
Signed-off-by: Joao Paulo <joaolrpaulo@gmail.com>
Signed-off-by: TomorrowLandAce <joaolrpaulo@gmail.com>
zram: remove workqueue for freeing removed pending slot

Commit e7400d00b76a2eb057c3c2b7b679bdb9c3c698cb ("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>
Signed-off-by: Pranav Vashi <neobuddy89@gmail.com>
Signed-off-by: Joao Paulo <joaolrpaulo@gmail.com>
Signed-off-by: TomorrowLandAce <joaolrpaulo@gmail.com>
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>
Signed-off-by: Pranav Vashi <neobuddy89@gmail.com>
Signed-off-by: Joao Paulo <joaolrpaulo@gmail.com>
Signed-off-by: TomorrowLandAce <joaolrpaulo@gmail.com>
zram: avoid null access when fail to alloc meta

zram_meta_alloc could fail so caller should check it.  Otherwise, your
system will hang.

Signed-off-by: Minchan Kim <minchan@kernel.org>
Acked-by: Jerome Marchand <jmarchan@redhat.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Pranav Vashi <neobuddy89@gmail.com>
Signed-off-by: Joao Paulo <joaolrpaulo@gmail.com>
Signed-off-by: TomorrowLandAce <joaolrpaulo@gmail.com>
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>
Signed-off-by: Pranav Vashi <neobuddy89@gmail.com>
Signed-off-by: Joao Paulo <joaolrpaulo@gmail.com>
Signed-off-by: TomorrowLandAce <joaolrpaulo@gmail.com>
zram: do not pass rw argument to __zram_make_request()

Do not pass rw argument down the __zram_make_request() -> zram_bvec_rw()
chain, decode it in zram_bvec_rw() instead.  Besides, this is the place
where we distinguish READ and WRITE bio data directions, so account zram
RW stats here, instead of __zram_make_request().  This also allows to
account a real number of zram READ/WRITE operations, not just requests
(single RW request may cause a number of zram RW ops with separate
locking, compression/decompression, etc).

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>
Signed-off-by: Pranav Vashi <neobuddy89@gmail.com>
Signed-off-by: Joao Paulo <joaolrpaulo@gmail.com>
Signed-off-by: TomorrowLandAce <joaolrpaulo@gmail.com>
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>
Signed-off-by: Pranav Vashi <neobuddy89@gmail.com>
Signed-off-by: Joao Paulo <joaolrpaulo@gmail.com>
Signed-off-by: TomorrowLandAce <joaolrpaulo@gmail.com>
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>
Signed-off-by: Pranav Vashi <neobuddy89@gmail.com>
Signed-off-by: Joao Paulo <joaolrpaulo@gmail.com>
Signed-off-by: TomorrowLandAce <joaolrpaulo@gmail.com>
zram: remove zram stats code duplication

Introduce ZRAM_ATTR_RO macro that generates device_attribute and default
ATTR show() function for existing atomic64_t zram stats.

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>
Signed-off-by: Pranav Vashi <neobuddy89@gmail.com>
Signed-off-by: Joao Paulo <joaolrpaulo@gmail.com>
Signed-off-by: TomorrowLandAce <joaolrpaulo@gmail.com>
zram: report failed read and write stats

zram accounted but did not report numbers of failed read and write
queries.  make these stats available as failed_reads and failed_writes
attrs.

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>
Signed-off-by: Pranav Vashi <neobuddy89@gmail.com>
Signed-off-by: Joao Paulo <joaolrpaulo@gmail.com>
Signed-off-by: TomorrowLandAce <joaolrpaulo@gmail.com>
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>
Signed-off-by: Pranav Vashi <neobuddy89@gmail.com>
Signed-off-by: Joao Paulo <joaolrpaulo@gmail.com>
Signed-off-by: TomorrowLandAce <joaolrpaulo@gmail.com>
zram: move zram size warning to documentation

Move zram warning about disksize and size of memory correlation to zram
documentation.

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>
Signed-off-by: Pranav Vashi <neobuddy89@gmail.com>
Signed-off-by: Joao Paulo <joaolrpaulo@gmail.com>
Signed-off-by: TomorrowLandAce <joaolrpaulo@gmail.com>
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>
Signed-off-by: Pranav Vashi <neobuddy89@gmail.com>
Signed-off-by: Joao Paulo <joaolrpaulo@gmail.com>
Signed-off-by: TomorrowLandAce <joaolrpaulo@gmail.com>
zram: delete zram_init_device()

allocate new `zram_meta' in disksize_store() only for uninitialised zram
device, saving a number of allocations and deallocations in case if
disksize_store() was called on currently used device.  at the same time
zram_meta stack variable is not necessary, because we can set ->meta
directly.  there is also no need in setting QUEUE_FLAG_NONROT queue on
every disksize_store(), set it once during device creation.

[minchan@kernel.org: handle zram->meta alloc fail case]
[minchan@kernel.org: prevent lockdep spew of init_lock]
Signed-off-by: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
Signed-off-by: Minchan Kim <minchan@kernel.org>
Acked-by: Jerome Marchand <jmarchan@redhat.com>
Cc: Sasha Levin <sasha.levin@oracle.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Pranav Vashi <neobuddy89@gmail.com>

Signed-off-by: Joao Paulo <joaolrpaulo@gmail.com>
Signed-off-by: TomorrowLandAce <joaolrpaulo@gmail.com>