f2fs: Pull in from upstream 3.13 kernel
Merge tag 'for-3.8-merge' of git://git.kernel.org/pub/scm/linux/kernel/git/jaegeuk/f2fs
Pull new F2FS filesystem from Jaegeuk Kim:
"Introduce a new file system, Flash-Friendly File System (F2FS), to
Linux 3.8.
Highlights:
- Add initial f2fs source codes
- Fix an endian conversion bug
- Fix build failures on random configs
- Fix the power-off-recovery routine
- Minor cleanup, coding style, and typos patches"
From the Kconfig help text:
F2FS is based on Log-structured File System (LFS), which supports
versatile "flash-friendly" features. The design has been focused on
addressing the fundamental issues in LFS, which are snowball effect
of wandering tree and high cleaning overhead.
Since flash-based storages show different characteristics according to
the internal geometry or flash memory management schemes aka FTL, F2FS
and tools support various parameters not only for configuring on-disk
layout, but also for selecting allocation and cleaning algorithms.
and there's an article by Neil Brown about it on lwn.net:
http://lwn.net/Articles/518988/
* tag 'for-3.8-merge' of git://git.kernel.org/pub/scm/linux/kernel/git/jaegeuk/f2fs: (36 commits)
f2fs: fix tracking parent inode number
f2fs: cleanup the f2fs_bio_alloc routine
f2fs: introduce accessor to retrieve number of dentry slots
f2fs: remove redundant call to f2fs_put_page in delete entry
f2fs: make use of GFP_F2FS_ZERO for setting gfp_mask
f2fs: rewrite f2fs_bio_alloc to make it simpler
f2fs: fix a typo in f2fs documentation
f2fs: remove unused variable
f2fs: move error condition for mkdir at proper place
f2fs: remove unneeded initialization
f2fs: check read only condition before beginning write out
f2fs: remove unneeded memset from init_once
f2fs: show error in case of invalid mount arguments
f2fs: fix the compiler warning for uninitialized use of variable
f2fs: resolve build failures
f2fs: adjust kernel coding style
f2fs: fix endian conversion bugs reported by sparse
f2fs: remove unneeded version.h header file from f2fs.h
f2fs: update the f2fs document
f2fs: update Kconfig and Makefile
...
Conflicts:
include/uapi/linux/magic.h
Merge tag 'for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/jaegeuk/f2fs
Pull f2fs bug fixes from Jaegeuk Kim:
"This patch-set includes two major bug fixes:
- incorrect IUsed provided by *df -i*, and
- lookup failure of parent inodes in corner cases.
[Other Bug Fixes]
- Fix error handling routines
- Trigger recovery process correctly
- Resolve build failures due to missing header files
[Etc]
- Add a MAINTAINERS entry for f2fs
- Fix and clean up variables, functions, and equations
- Avoid warnings during compilation"
* tag 'for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/jaegeuk/f2fs:
f2fs: unify string length declarations and usage
f2fs: clean up unused variables and return values
f2fs: clean up the start_bidx_of_node function
f2fs: remove unneeded variable from f2fs_sync_fs
f2fs: fix fsync_inode list addition logic and avoid invalid access to memory
f2fs: remove unneeded initialization of nr_dirty in dirty_seglist_info
f2fs: handle error from f2fs_iget_nowait
f2fs: fix equation of has_not_enough_free_secs()
f2fs: add MAINTAINERS entry
f2fs: return a default value for non-void function
f2fs: invalidate the node page if allocation is failed
f2fs: add missing #include <linux/prefetch.h>
f2fs: do f2fs_balance_fs in front of dir operations
f2fs: should recover orphan and fsync data
f2fs: fix handling errors got by f2fs_write_inode
f2fs: fix up f2fs_get_parent issue to retrieve correct parent inode number
f2fs: fix wrong calculation on f_files in statfs
f2fs: remove set_page_dirty for atomic f2fs_end_io_write
Merge tag 'f2fs-for-3.8-rc5' of git://git.kernel.org/pub/scm/linux/kernel/git/jaegeuk/f2fs
Pull f2fs fixes from Jaegeuk Kim:
o Support swap file and link generic_file_remap_pages
o Enhance the bio streaming flow and free section control
o Major bug fix on recovery routine
o Minor bug/warning fixes and code cleanups
* tag 'f2fs-for-3.8-rc5' of git://git.kernel.org/pub/scm/linux/kernel/git/jaegeuk/f2fs: (22 commits)
f2fs: use _safe() version of list_for_each
f2fs: add comments of start_bidx_of_node
f2fs: avoid issuing small bios due to several dirty node pages
f2fs: support swapfile
f2fs: add remap_pages as generic_file_remap_pages
f2fs: add __init to functions in init_f2fs_fs
f2fs: fix the debugfs entry creation path
f2fs: add global mutex_lock to protect f2fs_stat_list
f2fs: remove the blk_plug usage in f2fs_write_data_pages
f2fs: avoid redundant time update for parent directory in f2fs_delete_entry
f2fs: remove redundant call to set_blocksize in f2fs_fill_super
f2fs: move f2fs_balance_fs to punch_hole
f2fs: add f2fs_balance_fs in several interfaces
f2fs: revisit the f2fs_gc flow
f2fs: check return value during recovery
f2fs: avoid null dereference in f2fs_acl_from_disk
f2fs: initialize newly allocated dnode structure
f2fs: update f2fs partition info about SIT/NAT layout
f2fs: update f2fs document to reflect SIT/NAT layout correctly
f2fs: remove unneeded INIT_LIST_HEAD at few places
...
Merge tag 'f2fs-for-3.9' of git://git.kernel.org/pub/scm/linux/kernel/git/jaegeuk/f2fs
Pull f2fs update from Jaegeuk Kim:
"[Major bug fixes]
o Store device file information correctly
o Fix -EIO handling with respect to power-off-recovery
o Allocate blocks with global locks
o Fix wrong calculation of the SSR cost
[Cleanups]
o Get rid of fake on-stack dentries
[Enhancement]
o Support (un)freeze_fs
o Enhance the f2fs_gc flow
o Support 32-bit binary execution on 64-bit kernel"
* tag 'f2fs-for-3.9' of git://git.kernel.org/pub/scm/linux/kernel/git/jaegeuk/f2fs: (29 commits)
f2fs: avoid build warning
f2fs: add compat_ioctl to provide backward compatability
f2fs: fix calculation of max. gc cost in the SSR case
f2fs: clarify and enhance the f2fs_gc flow
f2fs: optimize the return condition for has_not_enough_free_secs
f2fs: make an accessor to get sections for particular block type
f2fs: mark gc_thread as NULL when thread creation is failed
f2fs: name gc task as per the block device
f2fs: remove unnecessary gc option check and balance_fs
f2fs: remove repeated F2FS_SET_SB_DIRT call
f2fs: when check superblock failed, try to check another superblock
f2fs: use F2FS_BLKSIZE to judge bloksize and page_cache_size
f2fs: add device name in debugfs
f2fs: stop repeated checking if cp is needed
f2fs: avoid balanc_fs during evict_inode
f2fs: remove the use of page_cache_release
f2fs: fix typo mistake for data_version description
f2fs: reorganize code for ra_node_page
f2fs: avoid redundant call to has_not_enough_free_secs in f2fs_gc
f2fs: add un/freeze_fs into super_operations
...
Merge tag 'f2fs-for-v3.10' of git://git.kernel.org/pub/scm/linux/kernel/git/jaegeuk/f2fs
Pull f2fs updates from Jaegeuk Kim:
"This patch-set includes the following major enhancement patches.
- introduce a new gloabl lock scheme
- add tracepoints on several major functions
- fix the overall cleaning process focused on victim selection
- apply the block plugging to merge IOs as much as possible
- enhance management of free nids and its list
- enhance the readahead mode for node pages
- address several cretical deadlock conditions
- reduce lock_page calls
The other minor bug fixes and enhancements are as follows.
- calculation mistakes: overflow
- bio types: READ, READA, and READ_SYNC
- fix the recovery flow, data races, and null pointer errors"
* tag 'f2fs-for-v3.10' of git://git.kernel.org/pub/scm/linux/kernel/git/jaegeuk/f2fs: (68 commits)
f2fs: cover free_nid management with spin_lock
f2fs: optimize scan_nat_page()
f2fs: code cleanup for scan_nat_page() and build_free_nids()
f2fs: bugfix for alloc_nid_failed()
f2fs: recover when journal contains deleted files
f2fs: continue to mount after failing recovery
f2fs: avoid deadlock during evict after f2fs_gc
f2fs: modify the number of issued pages to merge IOs
f2fs: remove useless #include <linux/proc_fs.h> as we're now using sysfs as debug entry.
f2fs: fix inconsistent using of NM_WOUT_THRESHOLD
f2fs: check truncation of mapping after lock_page
f2fs: enhance alloc_nid and build_free_nids flows
f2fs: add a tracepoint on f2fs_new_inode
f2fs: check nid == 0 in add_free_nid
f2fs: add REQ_META about metadata requests for submit
f2fs: give a chance to merge IOs by IO scheduler
f2fs: avoid frequent background GC
f2fs: add tracepoints to debug checkpoint request
f2fs: add tracepoints for write page operations
f2fs: add tracepoints to debug the block allocation
...
Merge tag 'for-f2fs-3.11' of git://git.kernel.org/pub/scm/linux/kernel/git/jaegeuk/f2fs
Pull f2fs updates from Jaegeuk Kim:
"This patch-set includes the following major enhancement patches:
- remount_fs callback function
- restore parent inode number to enhance the fsync performance
- xattr security labels
- reduce the number of redundant lock/unlock data pages
- avoid frequent write_inode calls
The other minor bug fixes are as follows.
- endian conversion bugs
- various bugs in the roll-forward recovery routine"
* tag 'for-f2fs-3.11' of git://git.kernel.org/pub/scm/linux/kernel/git/jaegeuk/f2fs: (56 commits)
f2fs: fix to recover i_size from roll-forward
f2fs: remove the unused argument "sbi" of func destroy_fsync_dnodes()
f2fs: remove reusing any prefree segments
f2fs: code cleanup and simplify in func {find/add}_gc_inode
f2fs: optimize the init_dirty_segmap function
f2fs: fix an endian conversion bug detected by sparse
f2fs: fix crc endian conversion
f2fs: add remount_fs callback support
f2fs: recover wrong pino after checkpoint during fsync
f2fs: optimize do_write_data_page()
f2fs: make locate_dirty_segment() as static
f2fs: remove unnecessary parameter "offset" from __add_sum_entry()
f2fs: avoid freqeunt write_inode calls
f2fs: optimise the truncate_data_blocks_range() range
f2fs: use the F2FS specific flags in f2fs_ioctl()
f2fs: sync dir->i_size with its block allocation
f2fs: fix i_blocks translation on various types of files
f2fs: set sb->s_fs_info before calling parse_options()
f2fs: support xattr security labels
f2fs: fix iget/iput of dir during recovery
...
Merge tag 'for-f2fs-3.12' of git://git.kernel.org/pub/scm/linux/kernel/git/jaegeuk/f2fs
Pull f2fs updates from Jaegeuk Kim:
"This patch-set includes the following major enhancement patches:
- support inline xattrs
- add sysfs support to control GCs explicitly
- add proc entry to show the current segment usage information
- improve the GC/SSR performance
The other bug fixes are as follows:
- avoid the overflow on status calculation
- fix some error handling routines
- fix inconsistent xattr states after power-off-recovery
- fix incorrect xattr node offset definition
- fix deadlock condition in fsync
- fix the fdatasync routine for power-off-recovery"
* tag 'for-f2fs-3.12' of git://git.kernel.org/pub/scm/linux/kernel/git/jaegeuk/f2fs: (40 commits)
f2fs: optimize gc for better performance
f2fs: merge more bios of node block writes
f2fs: avoid an overflow during utilization calculation
f2fs: trigger GC when there are prefree segments
f2fs: use strncasecmp() simplify the string comparison
f2fs: fix omitting to update inode page
f2fs: support the inline xattrs
f2fs: add the truncate_xattr_node function
f2fs: introduce __find_xattr for readability
f2fs: reserve the xattr space dynamically
f2fs: add flags for inline xattrs
f2fs: fix error return code in init_f2fs_fs()
f2fs: fix wrong BUG_ON condition
f2fs: fix memory leak when init f2fs filesystem fail
f2fs: fix a compound statement label error
f2fs: avoid writing inode redundantly when creating a file
f2fs: alloc_page() doesn't return an ERR_PTR
f2fs: should cover i_xattr_nid with its xattr node page lock
f2fs: check the free space first in new_node_page
f2fs: clean up the needless end 'return' of void function
...
Merge tag 'for-f2fs-3.13' of git://git.kernel.org/pub/scm/linux/kernel/git/jaegeuk/f2fs
Pull f2fs updates from Jaegeuk Kim:
"This patch-set includes the following major enhancement patches.
- add a sysfs to control reclaiming free segments
- enhance the f2fs global lock procedures
- enhance the victim selection flow
- wait for selected node blocks during fsync
- add some tracepoints
- add a config to remove abundant BUG_ONs
The other bug fixes are as follows.
- fix deadlock on acl operations
- fix some bugs with respect to orphan inodes
And, there are a bunch of cleanups"
* tag 'for-f2fs-3.13' of git://git.kernel.org/pub/scm/linux/kernel/git/jaegeuk/f2fs: (42 commits)
f2fs: issue more large discard command
f2fs: fix memory leak after kobject init failed in fill_super
f2fs: cleanup waiting routine for writeback pages in cp
f2fs: avoid to use a NULL point in destroy_segment_manager
f2fs: remove unnecessary TestClearPageError when wait pages writeback
f2fs: update f2fs document
f2fs: avoid to wait all the node blocks during fsync
f2fs: check all ones or zeros bitmap with bitops for better mount performance
f2fs: change the method of calculating the number summary blocks
f2fs: fix calculating incorrect free size when update xattr in __f2fs_setxattr
f2fs: add an option to avoid unnecessary BUG_ONs
f2fs: introduce CONFIG_F2FS_CHECK_FS for BUG_ON control
f2fs: fix a deadlock during init_acl procedure
f2fs: clean up acl flow for better readability
f2fs: remove unnecessary segment bitmap updates
f2fs: add tracepoint for vm_page_mkwrite
f2fs: add tracepoint for set_page_dirty
f2fs: remove redundant set_page_dirty from write_compacted_summaries
f2fs: add reclaiming control by sysfs
f2fs: introduce f2fs_balance_fs_bg for some background jobs
...
Change-Id: Ied5488471d49d64ce6abb4be19237c4e90829ff6
diff --git a/Documentation/filesystems/00-INDEX b/Documentation/filesystems/00-INDEX
index 8c624a1..ce5fd46 100644
--- a/Documentation/filesystems/00-INDEX
+++ b/Documentation/filesystems/00-INDEX
@@ -48,6 +48,8 @@
- info, mount options and specifications for the Ext4 filesystem.
files.txt
- info on file management in the Linux kernel.
+f2fs.txt
+ - info and mount options for the F2FS filesystem.
fuse.txt
- info on the Filesystem in User SpacE including mount options.
gfs2.txt
diff --git a/Documentation/filesystems/f2fs.txt b/Documentation/filesystems/f2fs.txt
new file mode 100644
index 0000000..a3fe811
--- /dev/null
+++ b/Documentation/filesystems/f2fs.txt
@@ -0,0 +1,502 @@
+================================================================================
+WHAT IS Flash-Friendly File System (F2FS)?
+================================================================================
+
+NAND flash memory-based storage devices, such as SSD, eMMC, and SD cards, have
+been equipped on a variety systems ranging from mobile to server systems. Since
+they are known to have different characteristics from the conventional rotating
+disks, a file system, an upper layer to the storage device, should adapt to the
+changes from the sketch in the design level.
+
+F2FS is a file system exploiting NAND flash memory-based storage devices, which
+is based on Log-structured File System (LFS). The design has been focused on
+addressing the fundamental issues in LFS, which are snowball effect of wandering
+tree and high cleaning overhead.
+
+Since a NAND flash memory-based storage device shows different characteristic
+according to its internal geometry or flash memory management scheme, namely FTL,
+F2FS and its tools support various parameters not only for configuring on-disk
+layout, but also for selecting allocation and cleaning algorithms.
+
+The following git tree provides the file system formatting tool (mkfs.f2fs),
+a consistency checking tool (fsck.f2fs), and a debugging tool (dump.f2fs).
+>> git://git.kernel.org/pub/scm/linux/kernel/git/jaegeuk/f2fs-tools.git
+
+For reporting bugs and sending patches, please use the following mailing list:
+>> linux-f2fs-devel@lists.sourceforge.net
+
+================================================================================
+BACKGROUND AND DESIGN ISSUES
+================================================================================
+
+Log-structured File System (LFS)
+--------------------------------
+"A log-structured file system writes all modifications to disk sequentially in
+a log-like structure, thereby speeding up both file writing and crash recovery.
+The log is the only structure on disk; it contains indexing information so that
+files can be read back from the log efficiently. In order to maintain large free
+areas on disk for fast writing, we divide the log into segments and use a
+segment cleaner to compress the live information from heavily fragmented
+segments." from Rosenblum, M. and Ousterhout, J. K., 1992, "The design and
+implementation of a log-structured file system", ACM Trans. Computer Systems
+10, 1, 26–52.
+
+Wandering Tree Problem
+----------------------
+In LFS, when a file data is updated and written to the end of log, its direct
+pointer block is updated due to the changed location. Then the indirect pointer
+block is also updated due to the direct pointer block update. In this manner,
+the upper index structures such as inode, inode map, and checkpoint block are
+also updated recursively. This problem is called as wandering tree problem [1],
+and in order to enhance the performance, it should eliminate or relax the update
+propagation as much as possible.
+
+[1] Bityutskiy, A. 2005. JFFS3 design issues. http://www.linux-mtd.infradead.org/
+
+Cleaning Overhead
+-----------------
+Since LFS is based on out-of-place writes, it produces so many obsolete blocks
+scattered across the whole storage. In order to serve new empty log space, it
+needs to reclaim these obsolete blocks seamlessly to users. This job is called
+as a cleaning process.
+
+The process consists of three operations as follows.
+1. A victim segment is selected through referencing segment usage table.
+2. It loads parent index structures of all the data in the victim identified by
+ segment summary blocks.
+3. It checks the cross-reference between the data and its parent index structure.
+4. It moves valid data selectively.
+
+This cleaning job may cause unexpected long delays, so the most important goal
+is to hide the latencies to users. And also definitely, it should reduce the
+amount of valid data to be moved, and move them quickly as well.
+
+================================================================================
+KEY FEATURES
+================================================================================
+
+Flash Awareness
+---------------
+- Enlarge the random write area for better performance, but provide the high
+ spatial locality
+- Align FS data structures to the operational units in FTL as best efforts
+
+Wandering Tree Problem
+----------------------
+- Use a term, “node”, that represents inodes as well as various pointer blocks
+- Introduce Node Address Table (NAT) containing the locations of all the “node”
+ blocks; this will cut off the update propagation.
+
+Cleaning Overhead
+-----------------
+- Support a background cleaning process
+- Support greedy and cost-benefit algorithms for victim selection policies
+- Support multi-head logs for static/dynamic hot and cold data separation
+- Introduce adaptive logging for efficient block allocation
+
+================================================================================
+MOUNT OPTIONS
+================================================================================
+
+background_gc=%s Turn on/off cleaning operations, namely garbage
+ collection, triggered in background when I/O subsystem is
+ idle. If background_gc=on, it will turn on the garbage
+ collection and if background_gc=off, garbage collection
+ will be truned off.
+ Default value for this option is on. So garbage
+ collection is on by default.
+disable_roll_forward Disable the roll-forward recovery routine
+discard Issue discard/TRIM commands when a segment is cleaned.
+no_heap Disable heap-style segment allocation which finds free
+ segments for data from the beginning of main area, while
+ for node from the end of main area.
+nouser_xattr Disable Extended User Attributes. Note: xattr is enabled
+ by default if CONFIG_F2FS_FS_XATTR is selected.
+noacl Disable POSIX Access Control List. Note: acl is enabled
+ by default if CONFIG_F2FS_FS_POSIX_ACL is selected.
+active_logs=%u Support configuring the number of active logs. In the
+ current design, f2fs supports only 2, 4, and 6 logs.
+ Default number is 6.
+disable_ext_identify Disable the extension list configured by mkfs, so f2fs
+ does not aware of cold files such as media files.
+inline_xattr Enable the inline xattrs feature.
+
+================================================================================
+DEBUGFS ENTRIES
+================================================================================
+
+/sys/kernel/debug/f2fs/ contains information about all the partitions mounted as
+f2fs. Each file shows the whole f2fs information.
+
+/sys/kernel/debug/f2fs/status includes:
+ - major file system information managed by f2fs currently
+ - average SIT information about whole segments
+ - current memory footprint consumed by f2fs.
+
+================================================================================
+SYSFS ENTRIES
+================================================================================
+
+Information about mounted f2f2 file systems can be found in
+/sys/fs/f2fs. Each mounted filesystem will have a directory in
+/sys/fs/f2fs based on its device name (i.e., /sys/fs/f2fs/sda).
+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_max_sleep_time This tuning parameter controls the maximum sleep
+ time for the garbage collection thread. Time is
+ in milliseconds.
+
+ gc_min_sleep_time This tuning parameter controls the minimum 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 aproach.
+
+ reclaim_segments This parameter controls the number of prefree
+ segments to be reclaimed. If the number of prefree
+ segments is larger than this number, f2fs tries to
+ conduct checkpoint to reclaim the prefree segments
+ to free segments. By default, 100 segments, 200MB.
+
+================================================================================
+USAGE
+================================================================================
+
+1. Download userland tools and compile them.
+
+2. Skip, if f2fs was compiled statically inside kernel.
+ Otherwise, insert the f2fs.ko module.
+ # insmod f2fs.ko
+
+3. Create a directory trying to mount
+ # mkdir /mnt/f2fs
+
+4. Format the block device, and then mount as f2fs
+ # mkfs.f2fs -l label /dev/block_device
+ # mount -t f2fs /dev/block_device /mnt/f2fs
+
+mkfs.f2fs
+---------
+The mkfs.f2fs is for the use of formatting a partition as the f2fs filesystem,
+which builds a basic on-disk layout.
+
+The options consist of:
+-l [label] : Give a volume label, up to 512 unicode name.
+-a [0 or 1] : Split start location of each area for heap-based allocation.
+ 1 is set by default, which performs this.
+-o [int] : Set overprovision ratio in percent over volume size.
+ 5 is set by default.
+-s [int] : Set the number of segments per section.
+ 1 is set by default.
+-z [int] : Set the number of sections per zone.
+ 1 is set by default.
+-e [str] : Set basic extension list. e.g. "mp3,gif,mov"
+-t [0 or 1] : Disable discard command or not.
+ 1 is set by default, which conducts discard.
+
+fsck.f2fs
+---------
+The fsck.f2fs is a tool to check the consistency of an f2fs-formatted
+partition, which examines whether the filesystem metadata and user-made data
+are cross-referenced correctly or not.
+Note that, initial version of the tool does not fix any inconsistency.
+
+The options consist of:
+ -d debug level [default:0]
+
+dump.f2fs
+---------
+The dump.f2fs shows the information of specific inode and dumps SSA and SIT to
+file. Each file is dump_ssa and dump_sit.
+
+The dump.f2fs is used to debug on-disk data structures of the f2fs filesystem.
+It shows on-disk inode information reconized by a given inode number, and is
+able to dump all the SSA and SIT entries into predefined files, ./dump_ssa and
+./dump_sit respectively.
+
+The options consist of:
+ -d debug level [default:0]
+ -i inode no (hex)
+ -s [SIT dump segno from #1~#2 (decimal), for all 0~-1]
+ -a [SSA dump segno from #1~#2 (decimal), for all 0~-1]
+
+Examples:
+# dump.f2fs -i [ino] /dev/sdx
+# dump.f2fs -s 0~-1 /dev/sdx (SIT dump)
+# dump.f2fs -a 0~-1 /dev/sdx (SSA dump)
+
+================================================================================
+DESIGN
+================================================================================
+
+On-disk Layout
+--------------
+
+F2FS divides the whole volume into a number of segments, each of which is fixed
+to 2MB in size. A section is composed of consecutive segments, and a zone
+consists of a set of sections. By default, section and zone sizes are set to one
+segment size identically, but users can easily modify the sizes by mkfs.
+
+F2FS splits the entire volume into six areas, and all the areas except superblock
+consists of multiple segments as described below.
+
+ align with the zone size <-|
+ |-> align with the segment size
+ _________________________________________________________________________
+ | | | Segment | Node | Segment | |
+ | Superblock | Checkpoint | Info. | Address | Summary | Main |
+ | (SB) | (CP) | Table (SIT) | Table (NAT) | Area (SSA) | |
+ |____________|_____2______|______N______|______N______|______N_____|__N___|
+ . .
+ . .
+ . .
+ ._________________________________________.
+ |_Segment_|_..._|_Segment_|_..._|_Segment_|
+ . .
+ ._________._________
+ |_section_|__...__|_
+ . .
+ .________.
+ |__zone__|
+
+- Superblock (SB)
+ : It is located at the beginning of the partition, and there exist two copies
+ to avoid file system crash. It contains basic partition information and some
+ default parameters of f2fs.
+
+- Checkpoint (CP)
+ : It contains file system information, bitmaps for valid NAT/SIT sets, orphan
+ inode lists, and summary entries of current active segments.
+
+- Segment Information Table (SIT)
+ : It contains segment information such as valid block count and bitmap for the
+ validity of all the blocks.
+
+- Node Address Table (NAT)
+ : It is composed of a block address table for all the node blocks stored in
+ Main area.
+
+- Segment Summary Area (SSA)
+ : It contains summary entries which contains the owner information of all the
+ data and node blocks stored in Main area.
+
+- Main Area
+ : It contains file and directory data including their indices.
+
+In order to avoid misalignment between file system and flash-based storage, F2FS
+aligns the start block address of CP with the segment size. Also, it aligns the
+start block address of Main area with the zone size by reserving some segments
+in SSA area.
+
+Reference the following survey for additional technical details.
+https://wiki.linaro.org/WorkingGroups/Kernel/Projects/FlashCardSurvey
+
+File System Metadata Structure
+------------------------------
+
+F2FS adopts the checkpointing scheme to maintain file system consistency. At
+mount time, F2FS first tries to find the last valid checkpoint data by scanning
+CP area. In order to reduce the scanning time, F2FS uses only two copies of CP.
+One of them always indicates the last valid data, which is called as shadow copy
+mechanism. In addition to CP, NAT and SIT also adopt the shadow copy mechanism.
+
+For file system consistency, each CP points to which NAT and SIT copies are
+valid, as shown as below.
+
+ +--------+----------+---------+
+ | CP | SIT | NAT |
+ +--------+----------+---------+
+ . . . .
+ . . . .
+ . . . .
+ +-------+-------+--------+--------+--------+--------+
+ | CP #0 | CP #1 | SIT #0 | SIT #1 | NAT #0 | NAT #1 |
+ +-------+-------+--------+--------+--------+--------+
+ | ^ ^
+ | | |
+ `----------------------------------------'
+
+Index Structure
+---------------
+
+The key data structure to manage the data locations is a "node". Similar to
+traditional file structures, F2FS has three types of node: inode, direct node,
+indirect node. F2FS assigns 4KB to an inode block which contains 923 data block
+indices, two direct node pointers, two indirect node pointers, and one double
+indirect node pointer as described below. One direct node block contains 1018
+data blocks, and one indirect node block contains also 1018 node blocks. Thus,
+one inode block (i.e., a file) covers:
+
+ 4KB * (923 + 2 * 1018 + 2 * 1018 * 1018 + 1018 * 1018 * 1018) := 3.94TB.
+
+ Inode block (4KB)
+ |- data (923)
+ |- direct node (2)
+ | `- data (1018)
+ |- indirect node (2)
+ | `- direct node (1018)
+ | `- data (1018)
+ `- double indirect node (1)
+ `- indirect node (1018)
+ `- direct node (1018)
+ `- data (1018)
+
+Note that, all the node blocks are mapped by NAT which means the location of
+each node is translated by the NAT table. In the consideration of the wandering
+tree problem, F2FS is able to cut off the propagation of node updates caused by
+leaf data writes.
+
+Directory Structure
+-------------------
+
+A directory entry occupies 11 bytes, which consists of the following attributes.
+
+- hash hash value of the file name
+- ino inode number
+- len the length of file name
+- type file type such as directory, symlink, etc
+
+A dentry block consists of 214 dentry slots and file names. Therein a bitmap is
+used to represent whether each dentry is valid or not. A dentry block occupies
+4KB with the following composition.
+
+ Dentry Block(4 K) = bitmap (27 bytes) + reserved (3 bytes) +
+ dentries(11 * 214 bytes) + file name (8 * 214 bytes)
+
+ [Bucket]
+ +--------------------------------+
+ |dentry block 1 | dentry block 2 |
+ +--------------------------------+
+ . .
+ . .
+ . [Dentry Block Structure: 4KB] .
+ +--------+----------+----------+------------+
+ | bitmap | reserved | dentries | file names |
+ +--------+----------+----------+------------+
+ [Dentry Block: 4KB] . .
+ . .
+ . .
+ +------+------+-----+------+
+ | hash | ino | len | type |
+ +------+------+-----+------+
+ [Dentry Structure: 11 bytes]
+
+F2FS implements multi-level hash tables for directory structure. Each level has
+a hash table with dedicated number of hash buckets as shown below. Note that
+"A(2B)" means a bucket includes 2 data blocks.
+
+----------------------
+A : bucket
+B : block
+N : MAX_DIR_HASH_DEPTH
+----------------------
+
+level #0 | A(2B)
+ |
+level #1 | A(2B) - A(2B)
+ |
+level #2 | A(2B) - A(2B) - A(2B) - A(2B)
+ . | . . . .
+level #N/2 | A(2B) - A(2B) - A(2B) - A(2B) - A(2B) - ... - A(2B)
+ . | . . . .
+level #N | A(4B) - A(4B) - A(4B) - A(4B) - A(4B) - ... - A(4B)
+
+The number of blocks and buckets are determined by,
+
+ ,- 2, if n < MAX_DIR_HASH_DEPTH / 2,
+ # of blocks in level #n = |
+ `- 4, Otherwise
+
+ ,- 2^n, if n < MAX_DIR_HASH_DEPTH / 2,
+ # of buckets in level #n = |
+ `- 2^((MAX_DIR_HASH_DEPTH / 2) - 1), Otherwise
+
+When F2FS finds a file name in a directory, at first a hash value of the file
+name is calculated. Then, F2FS scans the hash table in level #0 to find the
+dentry consisting of the file name and its inode number. If not found, F2FS
+scans the next hash table in level #1. In this way, F2FS scans hash tables in
+each levels incrementally from 1 to N. In each levels F2FS needs to scan only
+one bucket determined by the following equation, which shows O(log(# of files))
+complexity.
+
+ bucket number to scan in level #n = (hash value) % (# of buckets in level #n)
+
+In the case of file creation, F2FS finds empty consecutive slots that cover the
+file name. F2FS searches the empty slots in the hash tables of whole levels from
+1 to N in the same way as the lookup operation.
+
+The following figure shows an example of two cases holding children.
+ --------------> Dir <--------------
+ | |
+ child child
+
+ child - child [hole] - child
+
+ child - child - child [hole] - [hole] - child
+
+ Case 1: Case 2:
+ Number of children = 6, Number of children = 3,
+ File size = 7 File size = 7
+
+Default Block Allocation
+------------------------
+
+At runtime, F2FS manages six active logs inside "Main" area: Hot/Warm/Cold node
+and Hot/Warm/Cold data.
+
+- Hot node contains direct node blocks of directories.
+- Warm node contains direct node blocks except hot node blocks.
+- Cold node contains indirect node blocks
+- Hot data contains dentry blocks
+- Warm data contains data blocks except hot and cold data blocks
+- Cold data contains multimedia data or migrated data blocks
+
+LFS has two schemes for free space management: threaded log and copy-and-compac-
+tion. The copy-and-compaction scheme which is known as cleaning, is well-suited
+for devices showing very good sequential write performance, since free segments
+are served all the time for writing new data. However, it suffers from cleaning
+overhead under high utilization. Contrarily, the threaded log scheme suffers
+from random writes, but no cleaning process is needed. F2FS adopts a hybrid
+scheme where the copy-and-compaction scheme is adopted by default, but the
+policy is dynamically changed to the threaded log scheme according to the file
+system status.
+
+In order to align F2FS with underlying flash-based storage, F2FS allocates a
+segment in a unit of section. F2FS expects that the section size would be the
+same as the unit size of garbage collection in FTL. Furthermore, with respect
+to the mapping granularity in FTL, F2FS allocates each section of the active
+logs from different zones as much as possible, since FTL can write the data in
+the active logs into one allocation unit according to its mapping granularity.
+
+Cleaning process
+----------------
+
+F2FS does cleaning both on demand and in the background. On-demand cleaning is
+triggered when there are not enough free segments to serve VFS calls. Background
+cleaner is operated by a kernel thread, and triggers the cleaning job when the
+system is idle.
+
+F2FS supports two victim selection policies: greedy and cost-benefit algorithms.
+In the greedy algorithm, F2FS selects a victim segment having the smallest number
+of valid blocks. In the cost-benefit algorithm, F2FS selects a victim segment
+according to the segment age and the number of valid blocks in order to address
+log block thrashing problem in the greedy algorithm. F2FS adopts the greedy
+algorithm for on-demand cleaner, while background cleaner adopts cost-benefit
+algorithm.
+
+In order to identify whether the data in the victim segment are valid or not,
+F2FS manages a bitmap. Each bit represents the validity of a block, and the
+bitmap is composed of a bit stream covering whole blocks in main area.