mm/zsmalloc.c: correct comment for fullness group computation

The letter 'f' in "n <= N/f" stands for fullness_threshold_frac, not
1/fullness_threshold_frac.

Signed-off-by: Wang Sheng-Hui <shhuiw@gmail.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>
zsmalloc: simplify init_zspage free obj linking

Change zsmalloc init_zspage() logic to iterate through each object on each
of its pages, checking the offset to verify the object is on the current
page before linking it into the zspage.

The current zsmalloc init_zspage free object linking code has logic that
relies on there only being one page per zspage when PAGE_SIZE is a
multiple of class->size.  It calculates the number of objects for the
current page, and iterates through all of them plus one, to account for
the assumed partial object at the end of the page.  While this currently
works, the logic can be simplified to just link the object at each
successive offset until the offset is larger than PAGE_SIZE, which does
not rely on PAGE_SIZE being a multiple of class->size.

Signed-off-by: Dan Streetman <ddstreet@ieee.org>
Acked-by: Minchan Kim <minchan@kernel.org>
Cc: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
Cc: Nitin Gupta <ngupta@vflare.org>
Cc: Seth Jennings <sjennings@variantweb.net>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
zsmalloc: merge size_class to reduce fragmentation

zsmalloc has many size_classes to reduce fragmentation and they are in 16
bytes unit, for example, 16, 32, 48, etc., if PAGE_SIZE is 4096.  And,
zsmalloc has constraint that each zspage has 4 pages at maximum.

In this situation, we can see interesting aspect.  Let's think about
size_class for 1488, 1472, ..., 1376.  To prevent external fragmentation,
they uses 4 pages per zspage and so all they can contain 11 objects at
maximum.

16384 (4096 * 4) = 1488 * 11 + remains
16384 (4096 * 4) = 1472 * 11 + remains
16384 (4096 * 4) = ...
16384 (4096 * 4) = 1376 * 11 + remains

It means that they have same characteristics and classification between
them isn't needed.  If we use one size_class for them, we can reduce
fragementation and save some memory since both the 1488 and 1472 sized
classes can only fit 11 objects into 4 pages, and an object that's 1472
bytes can fit into an object that's 1488 bytes, merging these classes to
always use objects that are 1488 bytes will reduce the total number of
size classes.  And reducing the total number of size classes reduces
overall fragmentation, because a wider range of compressed pages can fit
into a single size class, leaving less unused objects in each size class.

For this purpose, this patch implement size_class merging.  If there is
size_class that have same pages_per_zspage and same number of objects per
zspage with previous size_class, we don't create new size_class.  Instead,
we use previous, same characteristic size_class.  With this way, above
example sizes (1488, 1472, ..., 1376) use just one size_class so we can
get much more memory utilization.

Below is result of my simple test.

TEST ENV: EXT4 on zram, mount with discard option WORKLOAD: untar kernel
source code, remove directory in descending order in size.  (drivers arch
fs sound include net Documentation firmware kernel tools)

Each line represents orig_data_size, compr_data_size, mem_used_total,
fragmentation overhead (mem_used - compr_data_size) and overhead ratio
(overhead to compr_data_size), respectively, after untar and remove
operation is executed.

* untar-nomerge.out

orig_size compr_size used_size overhead overhead_ratio
525.88MB 199.16MB 210.23MB  11.08MB 5.56%
288.32MB  97.43MB 105.63MB   8.20MB 8.41%
177.32MB  61.12MB  69.40MB   8.28MB 13.55%
146.47MB  47.32MB  56.10MB   8.78MB 18.55%
124.16MB  38.85MB  48.41MB   9.55MB 24.58%
103.93MB  31.68MB  40.93MB   9.25MB 29.21%
 84.34MB  22.86MB  32.72MB   9.86MB 43.13%
 66.87MB  14.83MB  23.83MB   9.00MB 60.70%
 60.67MB  11.11MB  18.60MB   7.49MB 67.48%
 55.86MB   8.83MB  16.61MB   7.77MB 88.03%
 53.32MB   8.01MB  15.32MB   7.31MB 91.24%

* untar-merge.out

orig_size compr_size used_size overhead overhead_ratio
526.23MB 199.18MB 209.81MB  10.64MB 5.34%
288.68MB  97.45MB 104.08MB   6.63MB 6.80%
177.68MB  61.14MB  66.93MB   5.79MB 9.47%
146.83MB  47.34MB  52.79MB   5.45MB 11.51%
124.52MB  38.87MB  44.30MB   5.43MB 13.96%
104.29MB  31.70MB  36.83MB   5.13MB 16.19%
 84.70MB  22.88MB  27.92MB   5.04MB 22.04%
 67.11MB  14.83MB  19.26MB   4.43MB 29.86%
 60.82MB  11.10MB  14.90MB   3.79MB 34.17%
 55.90MB   8.82MB  12.61MB   3.79MB 42.97%
 53.32MB   8.01MB  11.73MB   3.73MB 46.53%

As you can see above result, merged one has better utilization (overhead
ratio, 5th column) and uses less memory (mem_used_total, 3rd column).

Signed-off-by: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Cc: Minchan Kim <minchan@kernel.org>
Cc: Nitin Gupta <ngupta@vflare.org>
Cc: Jerome Marchand <jmarchan@redhat.com>
Cc: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
Reviewed-by: Dan Streetman <ddstreet@ieee.org>
Cc: Luigi Semenzato <semenzato@google.com>
Cc: <juno.choi@lge.com>
Cc: "seungho1.park" <seungho1.park@lge.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
zsmalloc: fix zs_init cpu notifier error handling

Mahendran Ganesh reported that zpool-enabled zsmalloc should not call
zpool_unregister_driver() from zs_init() if cpu notifier registration has
failed, because error handling is performed before we register the driver
via zpool_register_driver() call.

Factor out cpu notifier registration and unregistration code and fix
zs_init() error handling.

link: http://lkml.iu.edu//hypermail/linux/kernel/1411.1/04156.html
Signed-off-by: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
Reported-by: Mahendran Ganesh <opensource.ganesh@gmail.com>
Cc: Minchan Kim <minchan@kernel.org>
Cc: Nitin Gupta <ngupta@vflare.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
zsmalloc-fix-zs_init-cpu-notifier-error-handling-fix-2

squash bogus gcc warning

Cc: Mahendran Ganesh <opensource.ganesh@gmail.com>
Cc: Minchan Kim <minchan@kernel.org>
Cc: Nitin Gupta <ngupta@vflare.org>
Cc: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
zsmalloc-fix-zs_init-cpu-notifier-error-handling-fix

use __init and __exit

Cc: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
Cc: Minchan Kim <minchan@kernel.org>
Cc: Nitin Gupta <ngupta@vflare.org>
Cc: Mahendran Ganesh <opensource.ganesh@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
zsmalloc: correct fragile [kmap|kunmap]_atomic use

The kunmap_atomic should use virtual address getting by kmap_atomic.
However, some pieces of code in zsmalloc uses modified address, not the
one got by kmap_atomic for kunmap_atomic.

It's okay for working because zsmalloc modifies the address inner
PAGE_SIZE bounday so it works with current kmap_atomic's implementation.
But it's still fragile with potential changing of kmap_atomic so let's
correct it.

I got a subtle bug when I implemented a new feature of zsmalloc
(compaction) due to a link's mishandling (the link was over page
boundary).  Although it was totally my mistake, it took a while to find
the cause because an unpredictable kmapped address was unmapped causing an
almost random crash.

Signed-off-by: Minchan Kim <minchan@kernel.org>
Cc: Nitin Gupta <ngupta@vflare.org>
Cc: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
Cc: Dan Streetman <ddstreet@ieee.org>
Cc: Seth Jennings <sjennings@variantweb.net>
Cc: Jerome Marchand <jmarchan@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
mm/zsmalloc: support allocating obj with size of ZS_MAX_ALLOC_SIZE

I sent a patch [1] for unnecessary check in zsmalloc.  And Minchan Kim
found zsmalloc even does not support allocating an obj with the size of
ZS_MAX_ALLOC_SIZE in some situations.

For example:
   In system with 64KB PAGE_SIZE and 32 bit of physical addr. Then:
   ZS_MIN_ALLOC_SIZE is 32 bytes which is calculated by:
      MAX(32, (ZS_MAX_PAGES_PER_ZSPAGE << PAGE_SHIFT >> OBJ_INDEX_BITS))
   ZS_MAX_ALLOC_SIZE is 64KB(in current code, is PAGE_SIZE)
   ZS_SIZE_CLASS_DELTA is 256 bytes
   So, ZS_SIZE_CLASSES = (ZS_MAX_ALLOC_SIZE - ZS_MIN_ALLOC_SIZE) /
                          ZS_SIZE_CLASS_DELTA + 1
                       = 256

   In zs_create_pool(), the max size obj which can be allocated will be:
      ZS_MIN_ALLOC_SIZE + i * ZS_SIZE_CLASS_DELTA = 32 + 255*256 = 65312

   We can see that 65312 < 65536 (ZS_MAX_ALLOC_SIZE). So we can NOT
   allocate objs with size ZS_MAX_ALLOC_SIZE(65536) which we promise upper
   users we can do.

 [1]  http://lkml.iu.edu/hypermail/linux/kernel/1411.2/03835.html
 [2]  http://lkml.iu.edu/hypermail/linux/kernel/1411.2/04534.html

This patch fixes this issue by dynamiclly calculating zs_size_classes when
module is loaded, allocates buffer with size ZS_MAX_ALLOC_SIZE.  Then the
max obj(size is ZS_MAX_ALLOC_SIZE) can be stored in it.

Signed-off-by: Mahendran Ganesh <opensource.ganesh@gmail.com>
Suggested-by: Minchan Kim <minchan@kernel.org>
Cc: Nitin Gupta <ngupta@vflare.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
mm/zsmalloc: avoid duplicate assignment of prev_class

In zs_create_pool(), prev_class is assigned (ZS_SIZE_CLASSES - 1) times.
And the prev_class only references to the previous size_class.  So we do
not need unnecessary assignement.

This patch assigns *prev_class* when a new size_class structure is
allocated and uses prev_class to check whether the first class has been
allocated.

Signed-off-by: Ganesh Mahendran <opensource.ganesh@gmail.com>
Cc: Minchan Kim <minchan@kernel.org>
Cc: Nitin Gupta <ngupta@vflare.org>
Reviewed-by: Dan Streetman <ddstreet@ieee.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>