Merge tag 'f2fs-for-5.6' of git://git.kernel.org/pub/scm/linux/kernel/git/jaegeuk/f2fs

Pull f2fs updates from Jaegeuk Kim:
 "In this series, we've implemented transparent compression
  experimentally. It supports LZO and LZ4, but will add more later as we
  investigate in the field more.

  At this point, the feature doesn't expose compressed space to user
  directly in order to guarantee potential data updates later to the
  space. Instead, the main goal is to reduce data writes to flash disk
  as much as possible, resulting in extending disk life time as well as
  relaxing IO congestion.

  Alternatively, we're also considering to add ioctl() to reclaim
  compressed space and show it to user after putting the immutable bit.

  Enhancements:
   - add compression support
   - avoid unnecessary locks in quota ops
   - harden power-cut scenario for zoned block devices
   - use private bio_set to avoid IO congestion
   - replace GC mutex with rwsem to serialize callers

  Bug fixes:
   - fix dentry consistency and memory corruption in rename()'s error case
   - fix wrong swap extent reports
   - fix casefolding bugs
   - change lock coverage to avoid deadlock
   - avoid GFP_KERNEL under f2fs_lock_op

  And, we've cleaned up sysfs entries to prepare no debugfs"

* tag 'f2fs-for-5.6' of git://git.kernel.org/pub/scm/linux/kernel/git/jaegeuk/f2fs: (31 commits)
  f2fs: fix race conditions in ->d_compare() and ->d_hash()
  f2fs: fix dcache lookup of !casefolded directories
  f2fs: Add f2fs stats to sysfs
  f2fs: delete duplicate information on sysfs nodes
  f2fs: change to use rwsem for gc_mutex
  f2fs: update f2fs document regarding to fsync_mode
  f2fs: add a way to turn off ipu bio cache
  f2fs: code cleanup for f2fs_statfs_project()
  f2fs: fix miscounted block limit in f2fs_statfs_project()
  f2fs: show the CP_PAUSE reason in checkpoint traces
  f2fs: fix deadlock allocating bio_post_read_ctx from mempool
  f2fs: remove unneeded check for error allocating bio_post_read_ctx
  f2fs: convert inline_dir early before starting rename
  f2fs: fix memleak of kobject
  f2fs: fix to add swap extent correctly
  f2fs: run fsck when getting bad inode during GC
  f2fs: support data compression
  f2fs: free sysfs kobject
  f2fs: declare nested quota_sem and remove unnecessary sems
  f2fs: don't put new_page twice in f2fs_rename
  ...

2 files changed, 219 insertions, 277 deletions

diff --git a/Documentation/ABI/testing/sysfs-fs-f2fs b/Documentation/ABI/testing/sysfs-fs-f2fs
index aedeae1e8ec1..1a6cd5397129 100644
--- a/Documentation/ABI/testing/sysfs-fs-f2fs
+++ b/Documentation/ABI/testing/sysfs-fs-f2fs
@@ -1,37 +1,40 @@
 What:		/sys/fs/f2fs/<disk>/gc_max_sleep_time
 Date:		July 2013
 Contact:	"Namjae Jeon" <namjae.jeon@samsung.com>
-Description:
-		 Controls the maximun sleep time for gc_thread. Time
-		 is in milliseconds.
+Description:	Controls the maximum sleep time for gc_thread. Time
+		is in milliseconds.
 
 What:		/sys/fs/f2fs/<disk>/gc_min_sleep_time
 Date:		July 2013
 Contact:	"Namjae Jeon" <namjae.jeon@samsung.com>
-Description:
-		 Controls the minimum sleep time for gc_thread. Time
-		 is in milliseconds.
+Description:	Controls the minimum sleep time for gc_thread. Time
+		is in milliseconds.
 
 What:		/sys/fs/f2fs/<disk>/gc_no_gc_sleep_time
 Date:		July 2013
 Contact:	"Namjae Jeon" <namjae.jeon@samsung.com>
-Description:
-		 Controls the default sleep time for gc_thread. Time
-		 is in milliseconds.
+Description:	Controls the default sleep time for gc_thread. Time
+		is in milliseconds.
 
 What:		/sys/fs/f2fs/<disk>/gc_idle
 Date:		July 2013
 Contact:	"Namjae Jeon" <namjae.jeon@samsung.com>
-Description:
-		 Controls the victim selection policy for garbage collection.
+Description:	Controls the victim selection policy for garbage collection.
+		Setting gc_idle = 0(default) will disable this option. Setting
+		gc_idle = 1 will select the Cost Benefit approach & setting
+		gc_idle = 2 will select the greedy approach.
 
 What:		/sys/fs/f2fs/<disk>/reclaim_segments
 Date:		October 2013
 Contact:	"Jaegeuk Kim" <jaegeuk.kim@samsung.com>
-Description:
-		 Controls the issue rate of segment discard commands.
-
-What:		/sys/fs/f2fs/<disk>/max_blkaddr
+Description:	This parameter controls the number of prefree segments to be
+		reclaimed. If the number of prefree segments is larger than
+		the number of segments in the proportion to the percentage
+		over total volume size, f2fs tries to conduct checkpoint to
+		reclaim the prefree segments to free segments.
+		By default, 5% over total # of segments.
+
+What:		/sys/fs/f2fs/<disk>/main_blkaddr
 Date:		November 2019
 Contact:	"Ramon Pantin" <pantin@google.com>
 Description:
@@ -40,227 +43,278 @@ Description:
 What:		/sys/fs/f2fs/<disk>/ipu_policy
 Date:		November 2013
 Contact:	"Jaegeuk Kim" <jaegeuk.kim@samsung.com>
-Description:
-		 Controls the in-place-update policy.
+Description:	Controls the in-place-update policy.
+		updates in f2fs. User can set:
+		0x01: F2FS_IPU_FORCE, 0x02: F2FS_IPU_SSR,
+		0x04: F2FS_IPU_UTIL,  0x08: F2FS_IPU_SSR_UTIL,
+		0x10: F2FS_IPU_FSYNC, 0x20: F2FS_IPU_ASYNC,
+		0x40: F2FS_IPU_NOCACHE.
+		Refer segment.h for details.
 
 What:		/sys/fs/f2fs/<disk>/min_ipu_util
 Date:		November 2013
 Contact:	"Jaegeuk Kim" <jaegeuk.kim@samsung.com>
-Description:
-		 Controls the FS utilization condition for the in-place-update
-		 policies.
+Description:	Controls the FS utilization condition for the in-place-update
+		policies. It is used by F2FS_IPU_UTIL and F2FS_IPU_SSR_UTIL policies.
 
 What:		/sys/fs/f2fs/<disk>/min_fsync_blocks
 Date:		September 2014
 Contact:	"Jaegeuk Kim" <jaegeuk@kernel.org>
-Description:
-		 Controls the dirty page count condition for the in-place-update
-		 policies.
+Description:	Controls the dirty page count condition for the in-place-update
+		policies.
 
 What:		/sys/fs/f2fs/<disk>/min_seq_blocks
 Date:		August 2018
 Contact:	"Jaegeuk Kim" <jaegeuk@kernel.org>
-Description:
-		 Controls the dirty page count condition for batched sequential
-		 writes in ->writepages.
-
+Description:	Controls the dirty page count condition for batched sequential
+		writes in writepages.
 
 What:		/sys/fs/f2fs/<disk>/min_hot_blocks
 Date:		March 2017
 Contact:	"Jaegeuk Kim" <jaegeuk@kernel.org>
-Description:
-		 Controls the dirty page count condition for redefining hot data.
+Description:	Controls the dirty page count condition for redefining hot data.
 
 What:		/sys/fs/f2fs/<disk>/min_ssr_sections
 Date:		October 2017
 Contact:	"Chao Yu" <yuchao0@huawei.com>
-Description:
-		 Controls the fee section threshold to trigger SSR allocation.
+Description:	Controls the free section threshold to trigger SSR allocation.
+		If this is large, SSR mode will be enabled early.
 
 What:		/sys/fs/f2fs/<disk>/max_small_discards
 Date:		November 2013
 Contact:	"Jaegeuk Kim" <jaegeuk.kim@samsung.com>
-Description:
-		 Controls the issue rate of small discard commands.
+Description:	Controls the issue rate of discard commands that consist of small
+		blocks less than 2MB. The candidates to be discarded are cached until
+		checkpoint is triggered, and issued during the checkpoint.
+		By default, it is disabled with 0.
 
-What:          /sys/fs/f2fs/<disk>/discard_granularity
-Date:          July 2017
-Contact:       "Chao Yu" <yuchao0@huawei.com>
-Description:
-		Controls discard granularity of inner discard thread, inner thread
+What:		/sys/fs/f2fs/<disk>/discard_granularity
+Date:		July 2017
+Contact:	"Chao Yu" <yuchao0@huawei.com>
+Description:	Controls discard granularity of inner discard thread. Inner thread
 		will not issue discards with size that is smaller than granularity.
-		The unit size is one block, now only support configuring in range
-		of [1, 512].
+		The unit size is one block(4KB), now only support configuring
+		in range of [1, 512]. Default value is 4(=16KB).
 
-What:          /sys/fs/f2fs/<disk>/umount_discard_timeout
-Date:          January 2019
-Contact:       "Jaegeuk Kim" <jaegeuk@kernel.org>
-Description:
-		Set timeout to issue discard commands during umount.
-		Default: 5 secs
+What:		/sys/fs/f2fs/<disk>/umount_discard_timeout
+Date:		January 2019
+Contact:	"Jaegeuk Kim" <jaegeuk@kernel.org>
+Description:	Set timeout to issue discard commands during umount.
+	        Default: 5 secs
 
 What:		/sys/fs/f2fs/<disk>/max_victim_search
 Date:		January 2014
 Contact:	"Jaegeuk Kim" <jaegeuk.kim@samsung.com>
-Description:
-		 Controls the number of trials to find a victim segment.
+Description:	Controls the number of trials to find a victim segment
+		when conducting SSR and cleaning operations. The default value
+		is 4096 which covers 8GB block address range.
 
 What:		/sys/fs/f2fs/<disk>/migration_granularity
 Date:		October 2018
 Contact:	"Chao Yu" <yuchao0@huawei.com>
-Description:
-		 Controls migration granularity of garbage collection on large
-		 section, it can let GC move partial segment{s} of one section
-		 in one GC cycle, so that dispersing heavy overhead GC to
-		 multiple lightweight one.
+Description:	Controls migration granularity of garbage collection on large
+		section, it can let GC move partial segment{s} of one section
+		in one GC cycle, so that dispersing heavy overhead GC to
+		multiple lightweight one.
 
 What:		/sys/fs/f2fs/<disk>/dir_level
 Date:		March 2014
 Contact:	"Jaegeuk Kim" <jaegeuk.kim@samsung.com>
-Description:
-		 Controls the directory level for large directory.
+Description:	Controls the directory level for large directory. If a
+		directory has a number of files, it can reduce the file lookup
+		latency by increasing this dir_level value. Otherwise, it
+		needs to decrease this value to reduce the space overhead.
+		The default value is 0.
 
 What:		/sys/fs/f2fs/<disk>/ram_thresh
 Date:		March 2014
 Contact:	"Jaegeuk Kim" <jaegeuk.kim@samsung.com>
-Description:
-		 Controls the memory footprint used by f2fs.
+Description:	Controls the memory footprint used by free nids and cached
+		nat entries. By default, 1 is set, which indicates
+		10 MB / 1 GB RAM.
 
 What:		/sys/fs/f2fs/<disk>/batched_trim_sections
 Date:		February 2015
 Contact:	"Jaegeuk Kim" <jaegeuk@kernel.org>
-Description:
-		 Controls the trimming rate in batch mode.
-		 <deprecated>
+Description:	Controls the trimming rate in batch mode.
+		<deprecated>
 
 What:		/sys/fs/f2fs/<disk>/cp_interval
 Date:		October 2015
 Contact:	"Jaegeuk Kim" <jaegeuk@kernel.org>
-Description:
-		 Controls the checkpoint timing.
+Description:	Controls the checkpoint timing, set to 60 seconds by default.
 
 What:		/sys/fs/f2fs/<disk>/idle_interval
 Date:		January 2016
 Contact:	"Jaegeuk Kim" <jaegeuk@kernel.org>
-Description:
-		 Controls the idle timing for all paths other than
-		 discard and gc path.
+Description:	Controls the idle timing of system, if there is no FS operation
+		during given interval.
+		Set to 5 seconds by default.
 
 What:		/sys/fs/f2fs/<disk>/discard_idle_interval
 Date:		September 2018
 Contact:	"Chao Yu" <yuchao0@huawei.com>
 Contact:	"Sahitya Tummala" <stummala@codeaurora.org>
-Description:
-		 Controls the idle timing for discard path.
+Description:	Controls the idle timing of discard thread given
+		this time interval.
+		Default is 5 secs.
 
 What:		/sys/fs/f2fs/<disk>/gc_idle_interval
 Date:		September 2018
 Contact:	"Chao Yu" <yuchao0@huawei.com>
 Contact:	"Sahitya Tummala" <stummala@codeaurora.org>
-Description:
-		 Controls the idle timing for gc path.
+Description:    Controls the idle timing for gc path. Set to 5 seconds by default.
 
 What:		/sys/fs/f2fs/<disk>/iostat_enable
 Date:		August 2017
 Contact:	"Chao Yu" <yuchao0@huawei.com>
-Description:
-		 Controls to enable/disable IO stat.
+Description:	Controls to enable/disable IO stat.
 
 What:		/sys/fs/f2fs/<disk>/ra_nid_pages
 Date:		October 2015
 Contact:	"Chao Yu" <chao2.yu@samsung.com>
-Description:
-		 Controls the count of nid pages to be readaheaded.
+Description:	Controls the count of nid pages to be readaheaded.
+		When building free nids, F2FS reads NAT blocks ahead for
+		speed up. Default is 0.
 
 What:		/sys/fs/f2fs/<disk>/dirty_nats_ratio
 Date:		January 2016
 Contact:	"Chao Yu" <chao2.yu@samsung.com>
-Description:
-		 Controls dirty nat entries ratio threshold, if current
-		 ratio exceeds configured threshold, checkpoint will
-		 be triggered for flushing dirty nat entries.
+Description:	Controls dirty nat entries ratio threshold, if current
+		ratio exceeds configured threshold, checkpoint will
+		be triggered for flushing dirty nat entries.
 
 What:		/sys/fs/f2fs/<disk>/lifetime_write_kbytes
 Date:		January 2016
 Contact:	"Shuoran Liu" <liushuoran@huawei.com>
-Description:
-		 Shows total written kbytes issued to disk.
+Description:	Shows total written kbytes issued to disk.
 
 What:		/sys/fs/f2fs/<disk>/features
 Date:		July 2017
 Contact:	"Jaegeuk Kim" <jaegeuk@kernel.org>
-Description:
-		 Shows all enabled features in current device.
+Description:	Shows all enabled features in current device.
 
 What:		/sys/fs/f2fs/<disk>/inject_rate
 Date:		May 2016
 Contact:	"Sheng Yong" <shengyong1@huawei.com>
-Description:
-		 Controls the injection rate.
+Description:	Controls the injection rate of arbitrary faults.
 
 What:		/sys/fs/f2fs/<disk>/inject_type
 Date:		May 2016
 Contact:	"Sheng Yong" <shengyong1@huawei.com>
-Description:
-		 Controls the injection type.
+Description:	Controls the injection type of arbitrary faults.
+
+What:		/sys/fs/f2fs/<disk>/dirty_segments
+Date:		October 2017
+Contact:	"Jaegeuk Kim" <jaegeuk@kernel.org>
+Description:	Shows the number of dirty segments.
 
 What:		/sys/fs/f2fs/<disk>/reserved_blocks
 Date:		June 2017
 Contact:	"Chao Yu" <yuchao0@huawei.com>
-Description:
-		 Controls target reserved blocks in system, the threshold
-		 is soft, it could exceed current available user space.
+Description:	Controls target reserved blocks in system, the threshold
+		is soft, it could exceed current available user space.
 
 What:		/sys/fs/f2fs/<disk>/current_reserved_blocks
 Date:		October 2017
 Contact:	"Yunlong Song" <yunlong.song@huawei.com>
 Contact:	"Chao Yu" <yuchao0@huawei.com>
-Description:
-		 Shows current reserved blocks in system, it may be temporarily
-		 smaller than target_reserved_blocks, but will gradually
-		 increase to target_reserved_blocks when more free blocks are
-		 freed by user later.
+Description:	Shows current reserved blocks in system, it may be temporarily
+		smaller than target_reserved_blocks, but will gradually
+		increase to target_reserved_blocks when more free blocks are
+		freed by user later.
 
 What:		/sys/fs/f2fs/<disk>/gc_urgent
 Date:		August 2017
 Contact:	"Jaegeuk Kim" <jaegeuk@kernel.org>
-Description:
-		 Do background GC agressively
+Description:	Do background GC agressively when set. When gc_urgent = 1,
+		background thread starts to do GC by given gc_urgent_sleep_time
+		interval. It is set to 0 by default.
 
 What:		/sys/fs/f2fs/<disk>/gc_urgent_sleep_time
 Date:		August 2017
 Contact:	"Jaegeuk Kim" <jaegeuk@kernel.org>
-Description:
-		 Controls sleep time of GC urgent mode
+Description:	Controls sleep time of GC urgent mode. Set to 500ms by default.
 
 What:		/sys/fs/f2fs/<disk>/readdir_ra
 Date:		November 2017
 Contact:	"Sheng Yong" <shengyong1@huawei.com>
-Description:
-		 Controls readahead inode block in readdir.
+Description:	Controls readahead inode block in readdir. Enabled by default.
+
+What:		/sys/fs/f2fs/<disk>/gc_pin_file_thresh
+Date:		January 2018
+Contact:	Jaegeuk Kim <jaegeuk@kernel.org>
+Description:	This indicates how many GC can be failed for the pinned
+		file. If it exceeds this, F2FS doesn't guarantee its pinning
+		state. 2048 trials is set by default.
 
 What:		/sys/fs/f2fs/<disk>/extension_list
 Date:		Feburary 2018
 Contact:	"Chao Yu" <yuchao0@huawei.com>
-Description:
-		 Used to control configure extension list:
-		 - Query: cat /sys/fs/f2fs/<disk>/extension_list
-		 - Add: echo '[h/c]extension' > /sys/fs/f2fs/<disk>/extension_list
-		 - Del: echo '[h/c]!extension' > /sys/fs/f2fs/<disk>/extension_list
-		 - [h] means add/del hot file extension
-		 - [c] means add/del cold file extension
+Description:	Used to control configure extension list:
+		- Query: cat /sys/fs/f2fs/<disk>/extension_list
+		- Add: echo '[h/c]extension' > /sys/fs/f2fs/<disk>/extension_list
+		- Del: echo '[h/c]!extension' > /sys/fs/f2fs/<disk>/extension_list
+		- [h] means add/del hot file extension
+		- [c] means add/del cold file extension
 
 What:		/sys/fs/f2fs/<disk>/unusable
 Date		April 2019
 Contact:	"Daniel Rosenberg" <drosen@google.com>
-Description:
-		If checkpoint=disable, it displays the number of blocks that are unusable.
-                If checkpoint=enable it displays the enumber of blocks that would be unusable
-                if checkpoint=disable were to be set.
+Description:	If checkpoint=disable, it displays the number of blocks that
+		are unusable.
+		If checkpoint=enable it displays the enumber of blocks that
+		would be unusable if checkpoint=disable were to be set.
 
 What:		/sys/fs/f2fs/<disk>/encoding
 Date		July 2019
 Contact:	"Daniel Rosenberg" <drosen@google.com>
-Description:
-		Displays name and version of the encoding set for the filesystem.
-                If no encoding is set, displays (none)
+Description:	Displays name and version of the encoding set for the filesystem.
+		If no encoding is set, displays (none)
+
+What:		/sys/fs/f2fs/<disk>/free_segments
+Date:		September 2019
+Contact:	"Hridya Valsaraju" <hridya@google.com>
+Description:	Number of free segments in disk.
+
+What:		/sys/fs/f2fs/<disk>/cp_foreground_calls
+Date:		September 2019
+Contact:	"Hridya Valsaraju" <hridya@google.com>
+Description:	Number of checkpoint operations performed on demand. Available when
+		CONFIG_F2FS_STAT_FS=y.
+
+What:		/sys/fs/f2fs/<disk>/cp_background_calls
+Date:		September 2019
+Contact:	"Hridya Valsaraju" <hridya@google.com>
+Description:	Number of checkpoint operations performed in the background to
+		free segments. Available when CONFIG_F2FS_STAT_FS=y.
+
+What:		/sys/fs/f2fs/<disk>/gc_foreground_calls
+Date:		September 2019
+Contact:	"Hridya Valsaraju" <hridya@google.com>
+Description:	Number of garbage collection operations performed on demand.
+		Available when CONFIG_F2FS_STAT_FS=y.
+
+What:		/sys/fs/f2fs/<disk>/gc_background_calls
+Date:		September 2019
+Contact:	"Hridya Valsaraju" <hridya@google.com>
+Description:	Number of garbage collection operations triggered in background.
+		Available when CONFIG_F2FS_STAT_FS=y.
+
+What:		/sys/fs/f2fs/<disk>/moved_blocks_foreground
+Date:		September 2019
+Contact:	"Hridya Valsaraju" <hridya@google.com>
+Description:	Number of blocks moved by garbage collection in foreground.
+		Available when CONFIG_F2FS_STAT_FS=y.
+
+What:		/sys/fs/f2fs/<disk>/moved_blocks_background
+Date:		September 2019
+Contact:	"Hridya Valsaraju" <hridya@google.com>
+Description:	Number of blocks moved by garbage collection in background.
+		Available when CONFIG_F2FS_STAT_FS=y.
+
+What:		/sys/fs/f2fs/<disk>/avg_vblocks
+Date:		September 2019
+Contact:	"Hridya Valsaraju" <hridya@google.com>
+Description:	Average number of valid blocks.
+		Available when CONFIG_F2FS_STAT_FS=y.
diff --git a/Documentation/filesystems/f2fs.txt b/Documentation/filesystems/f2fs.txt
index 3135b80df6da..4eb3e2ddd00e 100644
--- a/Documentation/filesystems/f2fs.txt
+++ b/Documentation/filesystems/f2fs.txt
@@ -235,6 +235,17 @@ checkpoint=%s[:%u[%]]     Set to "disable" to turn off checkpointing. Set to "en
                        hide up to all remaining free space. The actual space that
                        would be unusable can be viewed at /sys/fs/f2fs/<disk>/unusable
                        This space is reclaimed once checkpoint=enable.
+compress_algorithm=%s  Control compress algorithm, currently f2fs supports "lzo"
+                       and "lz4" algorithm.
+compress_log_size=%u   Support configuring compress cluster size, the size will
+                       be 4KB * (1 << %u), 16KB is minimum size, also it's
+                       default size.
+compress_extension=%s  Support adding specified extension, so that f2fs can enable
+                       compression on those corresponding files, e.g. if all files
+                       with '.ext' has high compression rate, we can set the '.ext'
+                       on compression extension list and enable compression on
+                       these file by default rather than to enable it via ioctl.
+                       For other files, we can still enable compression via ioctl.
 
 ================================================================================
 DEBUGFS ENTRIES
@@ -259,170 +270,6 @@ The files in each per-device directory are shown in table below.
 
 Files in /sys/fs/f2fs/<devname>
 (see also Documentation/ABI/testing/sysfs-fs-f2fs)
-..............................................................................
- File                         Content
-
- gc_urgent_sleep_time         This parameter controls sleep time for gc_urgent.
-                              500 ms is set by default. See above gc_urgent.
-
- gc_min_sleep_time            This tuning parameter controls the minimum sleep
-                              time for the garbage collection thread. Time is
-                              in milliseconds.
-
- gc_max_sleep_time            This tuning parameter controls the maximum sleep
-                              time for the garbage collection thread. Time is
-                              in milliseconds.
-
- gc_no_gc_sleep_time          This tuning parameter controls the default sleep
-                              time for the garbage collection thread. Time is
-                              in milliseconds.
-
- gc_idle                      This parameter controls the selection of victim
-                              policy for garbage collection. Setting gc_idle = 0
-                              (default) will disable this option. Setting
-                              gc_idle = 1 will select the Cost Benefit approach
-                              & setting gc_idle = 2 will select the greedy approach.
-
- gc_urgent                    This parameter controls triggering background GCs
-                              urgently or not. Setting gc_urgent = 0 [default]
-                              makes back to default behavior, while if it is set
-                              to 1, background thread starts to do GC by given
-                              gc_urgent_sleep_time interval.
-
- reclaim_segments             This parameter controls the number of prefree
-                              segments to be reclaimed. If the number of prefree
-			      segments is larger than the number of segments
-			      in the proportion to the percentage over total
-			      volume size, f2fs tries to conduct checkpoint to
-			      reclaim the prefree segments to free segments.
-			      By default, 5% over total # of segments.
-
- main_blkaddr                 This value gives the first block address of
-			      MAIN area in the partition.
-
- max_small_discards	      This parameter controls the number of discard
-			      commands that consist small blocks less than 2MB.
-			      The candidates to be discarded are cached until
-			      checkpoint is triggered, and issued during the
-			      checkpoint. By default, it is disabled with 0.
-
- discard_granularity	      This parameter controls the granularity of discard
-			      command size. It will issue discard commands iif
-			      the size is larger than given granularity. Its
-			      unit size is 4KB, and 4 (=16KB) is set by default.
-			      The maximum value is 128 (=512KB).
-
- reserved_blocks	      This parameter indicates the number of blocks that
-			      f2fs reserves internally for root.
-
- batched_trim_sections	      This parameter controls the number of sections
-                              to be trimmed out in batch mode when FITRIM
-                              conducts. 32 sections is set by default.
-
- ipu_policy                   This parameter controls the policy of in-place
-                              updates in f2fs. There are five policies:
-                               0x01: F2FS_IPU_FORCE, 0x02: F2FS_IPU_SSR,
-                               0x04: F2FS_IPU_UTIL,  0x08: F2FS_IPU_SSR_UTIL,
-                               0x10: F2FS_IPU_FSYNC.
-
- min_ipu_util                 This parameter controls the threshold to trigger
-                              in-place-updates. The number indicates percentage
-                              of the filesystem utilization, and used by
-                              F2FS_IPU_UTIL and F2FS_IPU_SSR_UTIL policies.
-
- min_fsync_blocks             This parameter controls the threshold to trigger
-                              in-place-updates when F2FS_IPU_FSYNC mode is set.
-			      The number indicates the number of dirty pages
-			      when fsync needs to flush on its call path. If
-			      the number is less than this value, it triggers
-			      in-place-updates.
-
- min_seq_blocks		      This parameter controls the threshold to serialize
-			      write IOs issued by multiple threads in parallel.
-
- min_hot_blocks		      This parameter controls the threshold to allocate
-			      a hot data log for pending data blocks to write.
-
- min_ssr_sections	      This parameter adds the threshold when deciding
-			      SSR block allocation. If this is large, SSR mode
-			      will be enabled early.
-
- ram_thresh                   This parameter controls the memory footprint used
-			      by free nids and cached nat entries. By default,
-			      1 is set, which indicates 10 MB / 1 GB RAM.
-
- ra_nid_pages		      When building free nids, F2FS reads NAT blocks
-			      ahead for speed up. Default is 0.
-
- dirty_nats_ratio	      Given dirty ratio of cached nat entries, F2FS
-			      determines flushing them in background.
-
- max_victim_search	      This parameter controls the number of trials to
-			      find a victim segment when conducting SSR and
-			      cleaning operations. The default value is 4096
-			      which covers 8GB block address range.
-
- migration_granularity	      For large-sized sections, F2FS can stop GC given
-			      this granularity instead of reclaiming entire
-			      section.
-
- dir_level                    This parameter controls the directory level to
-			      support large directory. If a directory has a
-			      number of files, it can reduce the file lookup
-			      latency by increasing this dir_level value.
-			      Otherwise, it needs to decrease this value to
-			      reduce the space overhead. The default value is 0.
-
- cp_interval		      F2FS tries to do checkpoint periodically, 60 secs
-			      by default.
-
- idle_interval		      F2FS detects system is idle, if there's no F2FS
-			      operations during given interval, 5 secs by
-			      default.
-
- discard_idle_interval	      F2FS detects the discard thread is idle, given
-			      time interval. Default is 5 secs.
-
- gc_idle_interval	      F2FS detects the GC thread is idle, given time
-			      interval. Default is 5 secs.
-
- umount_discard_timeout       When unmounting the disk, F2FS waits for finishing
-			      queued discard commands which can take huge time.
-			      This gives time out for it, 5 secs by default.
-
- iostat_enable		      This controls to enable/disable iostat in F2FS.
-
- readdir_ra		      This enables/disabled readahead of inode blocks
-			      in readdir, and default is enabled.
-
- gc_pin_file_thresh	      This indicates how many GC can be failed for the
-			      pinned file. If it exceeds this, F2FS doesn't
-			      guarantee its pinning state. 2048 trials is set
-			      by default.
-
- extension_list		      This enables to change extension_list for hot/cold
-			      files in runtime.
-
- inject_rate		      This controls injection rate of arbitrary faults.
-
- inject_type		      This controls injection type of arbitrary faults.
-
- dirty_segments 	      This shows # of dirty segments.
-
- lifetime_write_kbytes	      This shows # of data written to the disk.
-
- features		      This shows current features enabled on F2FS.
-
- current_reserved_blocks      This shows # of blocks currently reserved.
-
- unusable                     If checkpoint=disable, this shows the number of
-                              blocks that are unusable.
-                              If checkpoint=enable it shows the number of blocks
-                              that would be unusable if checkpoint=disable were
-                              to be set.
-
-encoding 	              This shows the encoding used for casefolding.
-                              If casefolding is not enabled, returns (none)
 
 ================================================================================
 USAGE
@@ -840,3 +687,44 @@ zero or random data, which is useful to the below scenario where:
  4. address = fibmap(fd, offset)
  5. open(blkdev)
  6. write(blkdev, address)
+
+Compression implementation
+--------------------------
+
+- New term named cluster is defined as basic unit of compression, file can
+be divided into multiple clusters logically. One cluster includes 4 << n
+(n >= 0) logical pages, compression size is also cluster size, each of
+cluster can be compressed or not.
+
+- In cluster metadata layout, one special block address is used to indicate
+cluster is compressed one or normal one, for compressed cluster, following
+metadata maps cluster to [1, 4 << n - 1] physical blocks, in where f2fs
+stores data including compress header and compressed data.
+
+- In order to eliminate write amplification during overwrite, F2FS only
+support compression on write-once file, data can be compressed only when
+all logical blocks in file are valid and cluster compress ratio is lower
+than specified threshold.
+
+- To enable compression on regular inode, there are three ways:
+* chattr +c file
+* chattr +c dir; touch dir/file
+* mount w/ -o compress_extension=ext; touch file.ext
+
+Compress metadata layout:
+                             [Dnode Structure]
+             +-----------------------------------------------+
+             | cluster 1 | cluster 2 | ......... | cluster N |
+             +-----------------------------------------------+
+             .           .                       .           .
+       .                       .                .                      .
+  .         Compressed Cluster       .        .        Normal Cluster            .
++----------+---------+---------+---------+  +---------+---------+---------+---------+
+|compr flag| block 1 | block 2 | block 3 |  | block 1 | block 2 | block 3 | block 4 |
++----------+---------+---------+---------+  +---------+---------+---------+---------+
+           .                             .
+         .                                           .
+       .                                                           .
+      +-------------+-------------+----------+----------------------------+
+      | data length | data chksum | reserved |      compressed data       |
+      +-------------+-------------+----------+----------------------------+