xref: /linux/Documentation/filesystems/f2fs.rst (revision 151b1982be5d9f4ca641687ee1a4bb4fba5d26cf)
189272ca1SMauro Carvalho Chehab.. SPDX-License-Identifier: GPL-2.0
289272ca1SMauro Carvalho Chehab
389272ca1SMauro Carvalho Chehab==========================================
489272ca1SMauro Carvalho ChehabWHAT IS Flash-Friendly File System (F2FS)?
589272ca1SMauro Carvalho Chehab==========================================
689272ca1SMauro Carvalho Chehab
789272ca1SMauro Carvalho ChehabNAND flash memory-based storage devices, such as SSD, eMMC, and SD cards, have
889272ca1SMauro Carvalho Chehabbeen equipped on a variety systems ranging from mobile to server systems. Since
989272ca1SMauro Carvalho Chehabthey are known to have different characteristics from the conventional rotating
1089272ca1SMauro Carvalho Chehabdisks, a file system, an upper layer to the storage device, should adapt to the
1189272ca1SMauro Carvalho Chehabchanges from the sketch in the design level.
1289272ca1SMauro Carvalho Chehab
1389272ca1SMauro Carvalho ChehabF2FS is a file system exploiting NAND flash memory-based storage devices, which
1489272ca1SMauro Carvalho Chehabis based on Log-structured File System (LFS). The design has been focused on
1589272ca1SMauro Carvalho Chehabaddressing the fundamental issues in LFS, which are snowball effect of wandering
1689272ca1SMauro Carvalho Chehabtree and high cleaning overhead.
1789272ca1SMauro Carvalho Chehab
1889272ca1SMauro Carvalho ChehabSince a NAND flash memory-based storage device shows different characteristic
1989272ca1SMauro Carvalho Chehabaccording to its internal geometry or flash memory management scheme, namely FTL,
2089272ca1SMauro Carvalho ChehabF2FS and its tools support various parameters not only for configuring on-disk
2189272ca1SMauro Carvalho Chehablayout, but also for selecting allocation and cleaning algorithms.
2289272ca1SMauro Carvalho Chehab
2389272ca1SMauro Carvalho ChehabThe following git tree provides the file system formatting tool (mkfs.f2fs),
2489272ca1SMauro Carvalho Chehaba consistency checking tool (fsck.f2fs), and a debugging tool (dump.f2fs).
2589272ca1SMauro Carvalho Chehab
2689272ca1SMauro Carvalho Chehab- git://git.kernel.org/pub/scm/linux/kernel/git/jaegeuk/f2fs-tools.git
2789272ca1SMauro Carvalho Chehab
2889272ca1SMauro Carvalho ChehabFor reporting bugs and sending patches, please use the following mailing list:
2989272ca1SMauro Carvalho Chehab
3089272ca1SMauro Carvalho Chehab- linux-f2fs-devel@lists.sourceforge.net
3189272ca1SMauro Carvalho Chehab
3289272ca1SMauro Carvalho ChehabBackground and Design issues
3389272ca1SMauro Carvalho Chehab============================
3489272ca1SMauro Carvalho Chehab
3589272ca1SMauro Carvalho ChehabLog-structured File System (LFS)
3689272ca1SMauro Carvalho Chehab--------------------------------
3789272ca1SMauro Carvalho Chehab"A log-structured file system writes all modifications to disk sequentially in
3889272ca1SMauro Carvalho Chehaba log-like structure, thereby speeding up  both file writing and crash recovery.
3989272ca1SMauro Carvalho ChehabThe log is the only structure on disk; it contains indexing information so that
4089272ca1SMauro Carvalho Chehabfiles can be read back from the log efficiently. In order to maintain large free
4189272ca1SMauro Carvalho Chehabareas on disk for fast writing, we divide  the log into segments and use a
4289272ca1SMauro Carvalho Chehabsegment cleaner to compress the live information from heavily fragmented
4389272ca1SMauro Carvalho Chehabsegments." from Rosenblum, M. and Ousterhout, J. K., 1992, "The design and
4489272ca1SMauro Carvalho Chehabimplementation of a log-structured file system", ACM Trans. Computer Systems
4589272ca1SMauro Carvalho Chehab10, 1, 26–52.
4689272ca1SMauro Carvalho Chehab
4789272ca1SMauro Carvalho ChehabWandering Tree Problem
4889272ca1SMauro Carvalho Chehab----------------------
4989272ca1SMauro Carvalho ChehabIn LFS, when a file data is updated and written to the end of log, its direct
5089272ca1SMauro Carvalho Chehabpointer block is updated due to the changed location. Then the indirect pointer
5189272ca1SMauro Carvalho Chehabblock is also updated due to the direct pointer block update. In this manner,
5289272ca1SMauro Carvalho Chehabthe upper index structures such as inode, inode map, and checkpoint block are
5389272ca1SMauro Carvalho Chehabalso updated recursively. This problem is called as wandering tree problem [1],
5489272ca1SMauro Carvalho Chehaband in order to enhance the performance, it should eliminate or relax the update
5589272ca1SMauro Carvalho Chehabpropagation as much as possible.
5689272ca1SMauro Carvalho Chehab
5789272ca1SMauro Carvalho Chehab[1] Bityutskiy, A. 2005. JFFS3 design issues. http://www.linux-mtd.infradead.org/
5889272ca1SMauro Carvalho Chehab
5989272ca1SMauro Carvalho ChehabCleaning Overhead
6089272ca1SMauro Carvalho Chehab-----------------
6189272ca1SMauro Carvalho ChehabSince LFS is based on out-of-place writes, it produces so many obsolete blocks
6289272ca1SMauro Carvalho Chehabscattered across the whole storage. In order to serve new empty log space, it
6389272ca1SMauro Carvalho Chehabneeds to reclaim these obsolete blocks seamlessly to users. This job is called
6489272ca1SMauro Carvalho Chehabas a cleaning process.
6589272ca1SMauro Carvalho Chehab
6689272ca1SMauro Carvalho ChehabThe process consists of three operations as follows.
6789272ca1SMauro Carvalho Chehab
6889272ca1SMauro Carvalho Chehab1. A victim segment is selected through referencing segment usage table.
6989272ca1SMauro Carvalho Chehab2. It loads parent index structures of all the data in the victim identified by
7089272ca1SMauro Carvalho Chehab   segment summary blocks.
7189272ca1SMauro Carvalho Chehab3. It checks the cross-reference between the data and its parent index structure.
7289272ca1SMauro Carvalho Chehab4. It moves valid data selectively.
7389272ca1SMauro Carvalho Chehab
7489272ca1SMauro Carvalho ChehabThis cleaning job may cause unexpected long delays, so the most important goal
7589272ca1SMauro Carvalho Chehabis to hide the latencies to users. And also definitely, it should reduce the
7689272ca1SMauro Carvalho Chehabamount of valid data to be moved, and move them quickly as well.
7789272ca1SMauro Carvalho Chehab
7889272ca1SMauro Carvalho ChehabKey Features
7989272ca1SMauro Carvalho Chehab============
8089272ca1SMauro Carvalho Chehab
8189272ca1SMauro Carvalho ChehabFlash Awareness
8289272ca1SMauro Carvalho Chehab---------------
8389272ca1SMauro Carvalho Chehab- Enlarge the random write area for better performance, but provide the high
8489272ca1SMauro Carvalho Chehab  spatial locality
8589272ca1SMauro Carvalho Chehab- Align FS data structures to the operational units in FTL as best efforts
8689272ca1SMauro Carvalho Chehab
8789272ca1SMauro Carvalho ChehabWandering Tree Problem
8889272ca1SMauro Carvalho Chehab----------------------
8989272ca1SMauro Carvalho Chehab- Use a term, “node”, that represents inodes as well as various pointer blocks
9089272ca1SMauro Carvalho Chehab- Introduce Node Address Table (NAT) containing the locations of all the “node”
9189272ca1SMauro Carvalho Chehab  blocks; this will cut off the update propagation.
9289272ca1SMauro Carvalho Chehab
9389272ca1SMauro Carvalho ChehabCleaning Overhead
9489272ca1SMauro Carvalho Chehab-----------------
9589272ca1SMauro Carvalho Chehab- Support a background cleaning process
9689272ca1SMauro Carvalho Chehab- Support greedy and cost-benefit algorithms for victim selection policies
9789272ca1SMauro Carvalho Chehab- Support multi-head logs for static/dynamic hot and cold data separation
9889272ca1SMauro Carvalho Chehab- Introduce adaptive logging for efficient block allocation
9989272ca1SMauro Carvalho Chehab
10089272ca1SMauro Carvalho ChehabMount Options
10189272ca1SMauro Carvalho Chehab=============
10289272ca1SMauro Carvalho Chehab
10389272ca1SMauro Carvalho Chehab
1049aa1ccb4SJonathan Corbet======================== ============================================================
10589272ca1SMauro Carvalho Chehabbackground_gc=%s	 Turn on/off cleaning operations, namely garbage
10689272ca1SMauro Carvalho Chehab			 collection, triggered in background when I/O subsystem is
10789272ca1SMauro Carvalho Chehab			 idle. If background_gc=on, it will turn on the garbage
10889272ca1SMauro Carvalho Chehab			 collection and if background_gc=off, garbage collection
10989272ca1SMauro Carvalho Chehab			 will be turned off. If background_gc=sync, it will turn
11089272ca1SMauro Carvalho Chehab			 on synchronous garbage collection running in background.
11189272ca1SMauro Carvalho Chehab			 Default value for this option is on. So garbage
11289272ca1SMauro Carvalho Chehab			 collection is on by default.
1135911d2d1SChao Yugc_merge		 When background_gc is on, this option can be enabled to
1145911d2d1SChao Yu			 let background GC thread to handle foreground GC requests,
1155911d2d1SChao Yu			 it can eliminate the sluggish issue caused by slow foreground
1165911d2d1SChao Yu			 GC operation when GC is triggered from a process with limited
1175911d2d1SChao Yu			 I/O and CPU resources.
1185911d2d1SChao Yunogc_merge		 Disable GC merge feature.
11989272ca1SMauro Carvalho Chehabdisable_roll_forward	 Disable the roll-forward recovery routine
12089272ca1SMauro Carvalho Chehabnorecovery		 Disable the roll-forward recovery routine, mounted read-
12189272ca1SMauro Carvalho Chehab			 only (i.e., -o ro,disable_roll_forward)
12289272ca1SMauro Carvalho Chehabdiscard/nodiscard	 Enable/disable real-time discard in f2fs, if discard is
12389272ca1SMauro Carvalho Chehab			 enabled, f2fs will issue discard/TRIM commands when a
12489272ca1SMauro Carvalho Chehab			 segment is cleaned.
12589272ca1SMauro Carvalho Chehabno_heap			 Disable heap-style segment allocation which finds free
12689272ca1SMauro Carvalho Chehab			 segments for data from the beginning of main area, while
12789272ca1SMauro Carvalho Chehab			 for node from the end of main area.
12889272ca1SMauro Carvalho Chehabnouser_xattr		 Disable Extended User Attributes. Note: xattr is enabled
12989272ca1SMauro Carvalho Chehab			 by default if CONFIG_F2FS_FS_XATTR is selected.
13089272ca1SMauro Carvalho Chehabnoacl			 Disable POSIX Access Control List. Note: acl is enabled
13189272ca1SMauro Carvalho Chehab			 by default if CONFIG_F2FS_FS_POSIX_ACL is selected.
13289272ca1SMauro Carvalho Chehabactive_logs=%u		 Support configuring the number of active logs. In the
13389272ca1SMauro Carvalho Chehab			 current design, f2fs supports only 2, 4, and 6 logs.
13489272ca1SMauro Carvalho Chehab			 Default number is 6.
13589272ca1SMauro Carvalho Chehabdisable_ext_identify	 Disable the extension list configured by mkfs, so f2fs
136ca313c82SRandy Dunlap			 is not aware of cold files such as media files.
13789272ca1SMauro Carvalho Chehabinline_xattr		 Enable the inline xattrs feature.
13889272ca1SMauro Carvalho Chehabnoinline_xattr		 Disable the inline xattrs feature.
13989272ca1SMauro Carvalho Chehabinline_xattr_size=%u	 Support configuring inline xattr size, it depends on
14089272ca1SMauro Carvalho Chehab			 flexible inline xattr feature.
141ca313c82SRandy Dunlapinline_data		 Enable the inline data feature: Newly created small (<~3.4k)
14289272ca1SMauro Carvalho Chehab			 files can be written into inode block.
143ca313c82SRandy Dunlapinline_dentry		 Enable the inline dir feature: data in newly created
14489272ca1SMauro Carvalho Chehab			 directory entries can be written into inode block. The
14589272ca1SMauro Carvalho Chehab			 space of inode block which is used to store inline
14689272ca1SMauro Carvalho Chehab			 dentries is limited to ~3.4k.
14789272ca1SMauro Carvalho Chehabnoinline_dentry		 Disable the inline dentry feature.
14889272ca1SMauro Carvalho Chehabflush_merge		 Merge concurrent cache_flush commands as much as possible
14989272ca1SMauro Carvalho Chehab			 to eliminate redundant command issues. If the underlying
15089272ca1SMauro Carvalho Chehab			 device handles the cache_flush command relatively slowly,
15189272ca1SMauro Carvalho Chehab			 recommend to enable this option.
15289272ca1SMauro Carvalho Chehabnobarrier		 This option can be used if underlying storage guarantees
15389272ca1SMauro Carvalho Chehab			 its cached data should be written to the novolatile area.
15489272ca1SMauro Carvalho Chehab			 If this option is set, no cache_flush commands are issued
15589272ca1SMauro Carvalho Chehab			 but f2fs still guarantees the write ordering of all the
15689272ca1SMauro Carvalho Chehab			 data writes.
15789272ca1SMauro Carvalho Chehabfastboot		 This option is used when a system wants to reduce mount
15889272ca1SMauro Carvalho Chehab			 time as much as possible, even though normal performance
15989272ca1SMauro Carvalho Chehab			 can be sacrificed.
16089272ca1SMauro Carvalho Chehabextent_cache		 Enable an extent cache based on rb-tree, it can cache
16189272ca1SMauro Carvalho Chehab			 as many as extent which map between contiguous logical
16289272ca1SMauro Carvalho Chehab			 address and physical address per inode, resulting in
16389272ca1SMauro Carvalho Chehab			 increasing the cache hit ratio. Set by default.
16489272ca1SMauro Carvalho Chehabnoextent_cache		 Disable an extent cache based on rb-tree explicitly, see
16589272ca1SMauro Carvalho Chehab			 the above extent_cache mount option.
16689272ca1SMauro Carvalho Chehabnoinline_data		 Disable the inline data feature, inline data feature is
16789272ca1SMauro Carvalho Chehab			 enabled by default.
16889272ca1SMauro Carvalho Chehabdata_flush		 Enable data flushing before checkpoint in order to
16989272ca1SMauro Carvalho Chehab			 persist data of regular and symlink.
17089272ca1SMauro Carvalho Chehabreserve_root=%d		 Support configuring reserved space which is used for
17189272ca1SMauro Carvalho Chehab			 allocation from a privileged user with specified uid or
17289272ca1SMauro Carvalho Chehab			 gid, unit: 4KB, the default limit is 0.2% of user blocks.
17389272ca1SMauro Carvalho Chehabresuid=%d		 The user ID which may use the reserved blocks.
17489272ca1SMauro Carvalho Chehabresgid=%d		 The group ID which may use the reserved blocks.
17589272ca1SMauro Carvalho Chehabfault_injection=%d	 Enable fault injection in all supported types with
17689272ca1SMauro Carvalho Chehab			 specified injection rate.
17789272ca1SMauro Carvalho Chehabfault_type=%d		 Support configuring fault injection type, should be
17889272ca1SMauro Carvalho Chehab			 enabled with fault_injection option, fault type value
17989272ca1SMauro Carvalho Chehab			 is shown below, it supports single or combined type.
18089272ca1SMauro Carvalho Chehab
18189272ca1SMauro Carvalho Chehab			 ===================	  ===========
18289272ca1SMauro Carvalho Chehab			 Type_Name		  Type_Value
18389272ca1SMauro Carvalho Chehab			 ===================	  ===========
18489272ca1SMauro Carvalho Chehab			 FAULT_KMALLOC		  0x000000001
18589272ca1SMauro Carvalho Chehab			 FAULT_KVMALLOC		  0x000000002
18689272ca1SMauro Carvalho Chehab			 FAULT_PAGE_ALLOC	  0x000000004
18789272ca1SMauro Carvalho Chehab			 FAULT_PAGE_GET		  0x000000008
18889272ca1SMauro Carvalho Chehab			 FAULT_ALLOC_NID	  0x000000020
18989272ca1SMauro Carvalho Chehab			 FAULT_ORPHAN		  0x000000040
19089272ca1SMauro Carvalho Chehab			 FAULT_BLOCK		  0x000000080
19189272ca1SMauro Carvalho Chehab			 FAULT_DIR_DEPTH	  0x000000100
19289272ca1SMauro Carvalho Chehab			 FAULT_EVICT_INODE	  0x000000200
19389272ca1SMauro Carvalho Chehab			 FAULT_TRUNCATE		  0x000000400
19489272ca1SMauro Carvalho Chehab			 FAULT_READ_IO		  0x000000800
19589272ca1SMauro Carvalho Chehab			 FAULT_CHECKPOINT	  0x000001000
19689272ca1SMauro Carvalho Chehab			 FAULT_DISCARD		  0x000002000
19789272ca1SMauro Carvalho Chehab			 FAULT_WRITE_IO		  0x000004000
19889272ca1SMauro Carvalho Chehab			 ===================	  ===========
19989272ca1SMauro Carvalho Chehabmode=%s			 Control block allocation mode which supports "adaptive"
20089272ca1SMauro Carvalho Chehab			 and "lfs". In "lfs" mode, there should be no random
20189272ca1SMauro Carvalho Chehab			 writes towards main area.
20289272ca1SMauro Carvalho Chehabio_bits=%u		 Set the bit size of write IO requests. It should be set
20389272ca1SMauro Carvalho Chehab			 with "mode=lfs".
20489272ca1SMauro Carvalho Chehabusrquota		 Enable plain user disk quota accounting.
20589272ca1SMauro Carvalho Chehabgrpquota		 Enable plain group disk quota accounting.
20689272ca1SMauro Carvalho Chehabprjquota		 Enable plain project quota accounting.
20789272ca1SMauro Carvalho Chehabusrjquota=<file>	 Appoint specified file and type during mount, so that quota
20889272ca1SMauro Carvalho Chehabgrpjquota=<file>	 information can be properly updated during recovery flow,
20989272ca1SMauro Carvalho Chehabprjjquota=<file>	 <quota file>: must be in root directory;
21089272ca1SMauro Carvalho Chehabjqfmt=<quota type>	 <quota type>: [vfsold,vfsv0,vfsv1].
211ca313c82SRandy Dunlapoffusrjquota		 Turn off user journalled quota.
212ca313c82SRandy Dunlapoffgrpjquota		 Turn off group journalled quota.
213ca313c82SRandy Dunlapoffprjjquota		 Turn off project journalled quota.
21489272ca1SMauro Carvalho Chehabquota			 Enable plain user disk quota accounting.
21589272ca1SMauro Carvalho Chehabnoquota			 Disable all plain disk quota option.
21689272ca1SMauro Carvalho Chehabwhint_mode=%s		 Control which write hints are passed down to block
21789272ca1SMauro Carvalho Chehab			 layer. This supports "off", "user-based", and
21889272ca1SMauro Carvalho Chehab			 "fs-based".  In "off" mode (default), f2fs does not pass
21989272ca1SMauro Carvalho Chehab			 down hints. In "user-based" mode, f2fs tries to pass
22089272ca1SMauro Carvalho Chehab			 down hints given by users. And in "fs-based" mode, f2fs
22189272ca1SMauro Carvalho Chehab			 passes down hints with its policy.
22289272ca1SMauro Carvalho Chehaballoc_mode=%s		 Adjust block allocation policy, which supports "reuse"
22389272ca1SMauro Carvalho Chehab			 and "default".
22489272ca1SMauro Carvalho Chehabfsync_mode=%s		 Control the policy of fsync. Currently supports "posix",
22589272ca1SMauro Carvalho Chehab			 "strict", and "nobarrier". In "posix" mode, which is
22689272ca1SMauro Carvalho Chehab			 default, fsync will follow POSIX semantics and does a
22789272ca1SMauro Carvalho Chehab			 light operation to improve the filesystem performance.
22889272ca1SMauro Carvalho Chehab			 In "strict" mode, fsync will be heavy and behaves in line
22989272ca1SMauro Carvalho Chehab			 with xfs, ext4 and btrfs, where xfstest generic/342 will
23089272ca1SMauro Carvalho Chehab			 pass, but the performance will regress. "nobarrier" is
23189272ca1SMauro Carvalho Chehab			 based on "posix", but doesn't issue flush command for
23289272ca1SMauro Carvalho Chehab			 non-atomic files likewise "nobarrier" mount option.
233ed318a6cSEric Biggerstest_dummy_encryption
234ed318a6cSEric Biggerstest_dummy_encryption=%s
235ed318a6cSEric Biggers			 Enable dummy encryption, which provides a fake fscrypt
23689272ca1SMauro Carvalho Chehab			 context. The fake fscrypt context is used by xfstests.
237ed318a6cSEric Biggers			 The argument may be either "v1" or "v2", in order to
238ed318a6cSEric Biggers			 select the corresponding fscrypt policy version.
23989272ca1SMauro Carvalho Chehabcheckpoint=%s[:%u[%]]	 Set to "disable" to turn off checkpointing. Set to "enable"
24089272ca1SMauro Carvalho Chehab			 to reenable checkpointing. Is enabled by default. While
24189272ca1SMauro Carvalho Chehab			 disabled, any unmounting or unexpected shutdowns will cause
24289272ca1SMauro Carvalho Chehab			 the filesystem contents to appear as they did when the
24389272ca1SMauro Carvalho Chehab			 filesystem was mounted with that option.
24489272ca1SMauro Carvalho Chehab			 While mounting with checkpoint=disabled, the filesystem must
24589272ca1SMauro Carvalho Chehab			 run garbage collection to ensure that all available space can
24689272ca1SMauro Carvalho Chehab			 be used. If this takes too much time, the mount may return
24789272ca1SMauro Carvalho Chehab			 EAGAIN. You may optionally add a value to indicate how much
24889272ca1SMauro Carvalho Chehab			 of the disk you would be willing to temporarily give up to
24989272ca1SMauro Carvalho Chehab			 avoid additional garbage collection. This can be given as a
25089272ca1SMauro Carvalho Chehab			 number of blocks, or as a percent. For instance, mounting
25189272ca1SMauro Carvalho Chehab			 with checkpoint=disable:100% would always succeed, but it may
25289272ca1SMauro Carvalho Chehab			 hide up to all remaining free space. The actual space that
25389272ca1SMauro Carvalho Chehab			 would be unusable can be viewed at /sys/fs/f2fs/<disk>/unusable
25489272ca1SMauro Carvalho Chehab			 This space is reclaimed once checkpoint=enable.
255261eeb9cSDaeho Jeongcheckpoint_merge	 When checkpoint is enabled, this can be used to create a kernel
256261eeb9cSDaeho Jeong			 daemon and make it to merge concurrent checkpoint requests as
257261eeb9cSDaeho Jeong			 much as possible to eliminate redundant checkpoint issues. Plus,
258261eeb9cSDaeho Jeong			 we can eliminate the sluggish issue caused by slow checkpoint
259261eeb9cSDaeho Jeong			 operation when the checkpoint is done in a process context in
260261eeb9cSDaeho Jeong			 a cgroup having low i/o budget and cpu shares. To make this
261261eeb9cSDaeho Jeong			 do better, we set the default i/o priority of the kernel daemon
262261eeb9cSDaeho Jeong			 to "3", to give one higher priority than other kernel threads.
263261eeb9cSDaeho Jeong			 This is the same way to give a I/O priority to the jbd2
264261eeb9cSDaeho Jeong			 journaling thread of ext4 filesystem.
265261eeb9cSDaeho Jeongnocheckpoint_merge	 Disable checkpoint merge feature.
266f40f31caSLinus Torvaldscompress_algorithm=%s	 Control compress algorithm, currently f2fs supports "lzo",
2676d92b201SChao Yu			 "lz4", "zstd" and "lzo-rle" algorithm.
2683fde13f8SChao Yucompress_algorithm=%s:%d Control compress algorithm and its compress level, now, only
2693fde13f8SChao Yu			 "lz4" and "zstd" support compress level config.
2703fde13f8SChao Yu			 algorithm	level range
2713fde13f8SChao Yu			 lz4		3 - 16
2723fde13f8SChao Yu			 zstd		1 - 22
27389272ca1SMauro Carvalho Chehabcompress_log_size=%u	 Support configuring compress cluster size, the size will
27489272ca1SMauro Carvalho Chehab			 be 4KB * (1 << %u), 16KB is minimum size, also it's
27589272ca1SMauro Carvalho Chehab			 default size.
27689272ca1SMauro Carvalho Chehabcompress_extension=%s	 Support adding specified extension, so that f2fs can enable
27789272ca1SMauro Carvalho Chehab			 compression on those corresponding files, e.g. if all files
27889272ca1SMauro Carvalho Chehab			 with '.ext' has high compression rate, we can set the '.ext'
27989272ca1SMauro Carvalho Chehab			 on compression extension list and enable compression on
28089272ca1SMauro Carvalho Chehab			 these file by default rather than to enable it via ioctl.
28189272ca1SMauro Carvalho Chehab			 For other files, we can still enable compression via ioctl.
282fa679555SChao Yu			 Note that, there is one reserved special extension '*', it
283fa679555SChao Yu			 can be set to enable compression for all files.
284*151b1982SFengnan Changnocompress_extension=%s	   Support adding specified extension, so that f2fs can disable
285*151b1982SFengnan Chang			 compression on those corresponding files, just contrary to compression extension.
286*151b1982SFengnan Chang			 If you know exactly which files cannot be compressed, you can use this.
287*151b1982SFengnan Chang			 The same extension name can't appear in both compress and nocompress
288*151b1982SFengnan Chang			 extension at the same time.
289*151b1982SFengnan Chang			 If the compress extension specifies all files, the types specified by the
290*151b1982SFengnan Chang			 nocompress extension will be treated as special cases and will not be compressed.
291*151b1982SFengnan Chang			 Don't allow use '*' to specifie all file in nocompress extension.
292*151b1982SFengnan Chang			 After add nocompress_extension, the priority should be:
293*151b1982SFengnan Chang			 dir_flag < comp_extention,nocompress_extension < comp_file_flag,no_comp_file_flag.
294*151b1982SFengnan Chang			 See more in compression sections.
295*151b1982SFengnan Chang
296b28f047bSChao Yucompress_chksum		 Support verifying chksum of raw data in compressed cluster.
297602a16d5SDaeho Jeongcompress_mode=%s	 Control file compression mode. This supports "fs" and "user"
298602a16d5SDaeho Jeong			 modes. In "fs" mode (default), f2fs does automatic compression
299602a16d5SDaeho Jeong			 on the compression enabled files. In "user" mode, f2fs disables
300602a16d5SDaeho Jeong			 the automaic compression and gives the user discretion of
301602a16d5SDaeho Jeong			 choosing the target file and the timing. The user can do manual
302602a16d5SDaeho Jeong			 compression/decompression on the compression enabled files using
303602a16d5SDaeho Jeong			 ioctls.
3046ce19affSChao Yucompress_cache		 Support to use address space of a filesystem managed inode to
3056ce19affSChao Yu			 cache compressed block, in order to improve cache hit ratio of
3066ce19affSChao Yu			 random read.
3072324d50dSLinus Torvaldsinlinecrypt		 When possible, encrypt/decrypt the contents of encrypted
30827aacd28SSatya Tangirala			 files using the blk-crypto framework rather than
30927aacd28SSatya Tangirala			 filesystem-layer encryption. This allows the use of
31027aacd28SSatya Tangirala			 inline encryption hardware. The on-disk format is
31127aacd28SSatya Tangirala			 unaffected. For more details, see
31227aacd28SSatya Tangirala			 Documentation/block/inline-encryption.rst.
313093749e2SChao Yuatgc			 Enable age-threshold garbage collection, it provides high
314093749e2SChao Yu			 effectiveness and efficiency on background GC.
3159aa1ccb4SJonathan Corbet======================== ============================================================
31689272ca1SMauro Carvalho Chehab
31789272ca1SMauro Carvalho ChehabDebugfs Entries
31889272ca1SMauro Carvalho Chehab===============
31989272ca1SMauro Carvalho Chehab
32089272ca1SMauro Carvalho Chehab/sys/kernel/debug/f2fs/ contains information about all the partitions mounted as
32189272ca1SMauro Carvalho Chehabf2fs. Each file shows the whole f2fs information.
32289272ca1SMauro Carvalho Chehab
32389272ca1SMauro Carvalho Chehab/sys/kernel/debug/f2fs/status includes:
32489272ca1SMauro Carvalho Chehab
32589272ca1SMauro Carvalho Chehab - major file system information managed by f2fs currently
32689272ca1SMauro Carvalho Chehab - average SIT information about whole segments
32789272ca1SMauro Carvalho Chehab - current memory footprint consumed by f2fs.
32889272ca1SMauro Carvalho Chehab
32989272ca1SMauro Carvalho ChehabSysfs Entries
33089272ca1SMauro Carvalho Chehab=============
33189272ca1SMauro Carvalho Chehab
33289272ca1SMauro Carvalho ChehabInformation about mounted f2fs file systems can be found in
33389272ca1SMauro Carvalho Chehab/sys/fs/f2fs.  Each mounted filesystem will have a directory in
33489272ca1SMauro Carvalho Chehab/sys/fs/f2fs based on its device name (i.e., /sys/fs/f2fs/sda).
33589272ca1SMauro Carvalho ChehabThe files in each per-device directory are shown in table below.
33689272ca1SMauro Carvalho Chehab
33789272ca1SMauro Carvalho ChehabFiles in /sys/fs/f2fs/<devname>
33889272ca1SMauro Carvalho Chehab(see also Documentation/ABI/testing/sysfs-fs-f2fs)
33989272ca1SMauro Carvalho Chehab
34089272ca1SMauro Carvalho ChehabUsage
34189272ca1SMauro Carvalho Chehab=====
34289272ca1SMauro Carvalho Chehab
34389272ca1SMauro Carvalho Chehab1. Download userland tools and compile them.
34489272ca1SMauro Carvalho Chehab
34589272ca1SMauro Carvalho Chehab2. Skip, if f2fs was compiled statically inside kernel.
34689272ca1SMauro Carvalho Chehab   Otherwise, insert the f2fs.ko module::
34789272ca1SMauro Carvalho Chehab
34889272ca1SMauro Carvalho Chehab	# insmod f2fs.ko
34989272ca1SMauro Carvalho Chehab
350ca313c82SRandy Dunlap3. Create a directory to use when mounting::
35189272ca1SMauro Carvalho Chehab
35289272ca1SMauro Carvalho Chehab	# mkdir /mnt/f2fs
35389272ca1SMauro Carvalho Chehab
35489272ca1SMauro Carvalho Chehab4. Format the block device, and then mount as f2fs::
35589272ca1SMauro Carvalho Chehab
35689272ca1SMauro Carvalho Chehab	# mkfs.f2fs -l label /dev/block_device
35789272ca1SMauro Carvalho Chehab	# mount -t f2fs /dev/block_device /mnt/f2fs
35889272ca1SMauro Carvalho Chehab
35989272ca1SMauro Carvalho Chehabmkfs.f2fs
36089272ca1SMauro Carvalho Chehab---------
36189272ca1SMauro Carvalho ChehabThe mkfs.f2fs is for the use of formatting a partition as the f2fs filesystem,
36289272ca1SMauro Carvalho Chehabwhich builds a basic on-disk layout.
36389272ca1SMauro Carvalho Chehab
364568d2a1eSJaegeuk KimThe quick options consist of:
36589272ca1SMauro Carvalho Chehab
36689272ca1SMauro Carvalho Chehab===============    ===========================================================
36789272ca1SMauro Carvalho Chehab``-l [label]``     Give a volume label, up to 512 unicode name.
36889272ca1SMauro Carvalho Chehab``-a [0 or 1]``    Split start location of each area for heap-based allocation.
36989272ca1SMauro Carvalho Chehab
37089272ca1SMauro Carvalho Chehab                   1 is set by default, which performs this.
37189272ca1SMauro Carvalho Chehab``-o [int]``       Set overprovision ratio in percent over volume size.
37289272ca1SMauro Carvalho Chehab
37389272ca1SMauro Carvalho Chehab                   5 is set by default.
37489272ca1SMauro Carvalho Chehab``-s [int]``       Set the number of segments per section.
37589272ca1SMauro Carvalho Chehab
37689272ca1SMauro Carvalho Chehab                   1 is set by default.
37789272ca1SMauro Carvalho Chehab``-z [int]``       Set the number of sections per zone.
37889272ca1SMauro Carvalho Chehab
37989272ca1SMauro Carvalho Chehab                   1 is set by default.
38089272ca1SMauro Carvalho Chehab``-e [str]``       Set basic extension list. e.g. "mp3,gif,mov"
38189272ca1SMauro Carvalho Chehab``-t [0 or 1]``    Disable discard command or not.
38289272ca1SMauro Carvalho Chehab
38389272ca1SMauro Carvalho Chehab                   1 is set by default, which conducts discard.
38489272ca1SMauro Carvalho Chehab===============    ===========================================================
38589272ca1SMauro Carvalho Chehab
386ca313c82SRandy DunlapNote: please refer to the manpage of mkfs.f2fs(8) to get full option list.
387568d2a1eSJaegeuk Kim
38889272ca1SMauro Carvalho Chehabfsck.f2fs
38989272ca1SMauro Carvalho Chehab---------
39089272ca1SMauro Carvalho ChehabThe fsck.f2fs is a tool to check the consistency of an f2fs-formatted
39189272ca1SMauro Carvalho Chehabpartition, which examines whether the filesystem metadata and user-made data
39289272ca1SMauro Carvalho Chehabare cross-referenced correctly or not.
39389272ca1SMauro Carvalho ChehabNote that, initial version of the tool does not fix any inconsistency.
39489272ca1SMauro Carvalho Chehab
395568d2a1eSJaegeuk KimThe quick options consist of::
39689272ca1SMauro Carvalho Chehab
39789272ca1SMauro Carvalho Chehab  -d debug level [default:0]
39889272ca1SMauro Carvalho Chehab
399ca313c82SRandy DunlapNote: please refer to the manpage of fsck.f2fs(8) to get full option list.
400568d2a1eSJaegeuk Kim
40189272ca1SMauro Carvalho Chehabdump.f2fs
40289272ca1SMauro Carvalho Chehab---------
40389272ca1SMauro Carvalho ChehabThe dump.f2fs shows the information of specific inode and dumps SSA and SIT to
40489272ca1SMauro Carvalho Chehabfile. Each file is dump_ssa and dump_sit.
40589272ca1SMauro Carvalho Chehab
40689272ca1SMauro Carvalho ChehabThe dump.f2fs is used to debug on-disk data structures of the f2fs filesystem.
40789272ca1SMauro Carvalho ChehabIt shows on-disk inode information recognized by a given inode number, and is
40889272ca1SMauro Carvalho Chehabable to dump all the SSA and SIT entries into predefined files, ./dump_ssa and
40989272ca1SMauro Carvalho Chehab./dump_sit respectively.
41089272ca1SMauro Carvalho Chehab
41189272ca1SMauro Carvalho ChehabThe options consist of::
41289272ca1SMauro Carvalho Chehab
41389272ca1SMauro Carvalho Chehab  -d debug level [default:0]
41489272ca1SMauro Carvalho Chehab  -i inode no (hex)
41589272ca1SMauro Carvalho Chehab  -s [SIT dump segno from #1~#2 (decimal), for all 0~-1]
41689272ca1SMauro Carvalho Chehab  -a [SSA dump segno from #1~#2 (decimal), for all 0~-1]
41789272ca1SMauro Carvalho Chehab
41889272ca1SMauro Carvalho ChehabExamples::
41989272ca1SMauro Carvalho Chehab
42089272ca1SMauro Carvalho Chehab    # dump.f2fs -i [ino] /dev/sdx
42189272ca1SMauro Carvalho Chehab    # dump.f2fs -s 0~-1 /dev/sdx (SIT dump)
42289272ca1SMauro Carvalho Chehab    # dump.f2fs -a 0~-1 /dev/sdx (SSA dump)
42389272ca1SMauro Carvalho Chehab
424ca313c82SRandy DunlapNote: please refer to the manpage of dump.f2fs(8) to get full option list.
425568d2a1eSJaegeuk Kim
426568d2a1eSJaegeuk Kimsload.f2fs
427568d2a1eSJaegeuk Kim----------
428568d2a1eSJaegeuk KimThe sload.f2fs gives a way to insert files and directories in the exisiting disk
429568d2a1eSJaegeuk Kimimage. This tool is useful when building f2fs images given compiled files.
430568d2a1eSJaegeuk Kim
431ca313c82SRandy DunlapNote: please refer to the manpage of sload.f2fs(8) to get full option list.
432568d2a1eSJaegeuk Kim
433568d2a1eSJaegeuk Kimresize.f2fs
434568d2a1eSJaegeuk Kim-----------
435ca313c82SRandy DunlapThe resize.f2fs lets a user resize the f2fs-formatted disk image, while preserving
436568d2a1eSJaegeuk Kimall the files and directories stored in the image.
437568d2a1eSJaegeuk Kim
438ca313c82SRandy DunlapNote: please refer to the manpage of resize.f2fs(8) to get full option list.
439568d2a1eSJaegeuk Kim
440568d2a1eSJaegeuk Kimdefrag.f2fs
441568d2a1eSJaegeuk Kim-----------
442ca313c82SRandy DunlapThe defrag.f2fs can be used to defragment scattered written data as well as
443568d2a1eSJaegeuk Kimfilesystem metadata across the disk. This can improve the write speed by giving
444568d2a1eSJaegeuk Kimmore free consecutive space.
445568d2a1eSJaegeuk Kim
446ca313c82SRandy DunlapNote: please refer to the manpage of defrag.f2fs(8) to get full option list.
447568d2a1eSJaegeuk Kim
448568d2a1eSJaegeuk Kimf2fs_io
449568d2a1eSJaegeuk Kim-------
450568d2a1eSJaegeuk KimThe f2fs_io is a simple tool to issue various filesystem APIs as well as
451568d2a1eSJaegeuk Kimf2fs-specific ones, which is very useful for QA tests.
452568d2a1eSJaegeuk Kim
453ca313c82SRandy DunlapNote: please refer to the manpage of f2fs_io(8) to get full option list.
454568d2a1eSJaegeuk Kim
45589272ca1SMauro Carvalho ChehabDesign
45689272ca1SMauro Carvalho Chehab======
45789272ca1SMauro Carvalho Chehab
45889272ca1SMauro Carvalho ChehabOn-disk Layout
45989272ca1SMauro Carvalho Chehab--------------
46089272ca1SMauro Carvalho Chehab
46189272ca1SMauro Carvalho ChehabF2FS divides the whole volume into a number of segments, each of which is fixed
46289272ca1SMauro Carvalho Chehabto 2MB in size. A section is composed of consecutive segments, and a zone
46389272ca1SMauro Carvalho Chehabconsists of a set of sections. By default, section and zone sizes are set to one
46489272ca1SMauro Carvalho Chehabsegment size identically, but users can easily modify the sizes by mkfs.
46589272ca1SMauro Carvalho Chehab
46689272ca1SMauro Carvalho ChehabF2FS splits the entire volume into six areas, and all the areas except superblock
467ca313c82SRandy Dunlapconsist of multiple segments as described below::
46889272ca1SMauro Carvalho Chehab
46989272ca1SMauro Carvalho Chehab                                            align with the zone size <-|
47089272ca1SMauro Carvalho Chehab                 |-> align with the segment size
47189272ca1SMauro Carvalho Chehab     _________________________________________________________________________
47289272ca1SMauro Carvalho Chehab    |            |            |   Segment   |    Node     |   Segment  |      |
47389272ca1SMauro Carvalho Chehab    | Superblock | Checkpoint |    Info.    |   Address   |   Summary  | Main |
47489272ca1SMauro Carvalho Chehab    |    (SB)    |   (CP)     | Table (SIT) | Table (NAT) | Area (SSA) |      |
47589272ca1SMauro Carvalho Chehab    |____________|_____2______|______N______|______N______|______N_____|__N___|
47689272ca1SMauro Carvalho Chehab                                                                       .      .
47789272ca1SMauro Carvalho Chehab                                                             .                .
47889272ca1SMauro Carvalho Chehab                                                 .                            .
47989272ca1SMauro Carvalho Chehab                                    ._________________________________________.
48089272ca1SMauro Carvalho Chehab                                    |_Segment_|_..._|_Segment_|_..._|_Segment_|
48189272ca1SMauro Carvalho Chehab                                    .           .
48289272ca1SMauro Carvalho Chehab                                    ._________._________
48389272ca1SMauro Carvalho Chehab                                    |_section_|__...__|_
48489272ca1SMauro Carvalho Chehab                                    .            .
48589272ca1SMauro Carvalho Chehab		                    .________.
48689272ca1SMauro Carvalho Chehab	                            |__zone__|
48789272ca1SMauro Carvalho Chehab
48889272ca1SMauro Carvalho Chehab- Superblock (SB)
48989272ca1SMauro Carvalho Chehab   It is located at the beginning of the partition, and there exist two copies
49089272ca1SMauro Carvalho Chehab   to avoid file system crash. It contains basic partition information and some
49189272ca1SMauro Carvalho Chehab   default parameters of f2fs.
49289272ca1SMauro Carvalho Chehab
49389272ca1SMauro Carvalho Chehab- Checkpoint (CP)
49489272ca1SMauro Carvalho Chehab   It contains file system information, bitmaps for valid NAT/SIT sets, orphan
49589272ca1SMauro Carvalho Chehab   inode lists, and summary entries of current active segments.
49689272ca1SMauro Carvalho Chehab
49789272ca1SMauro Carvalho Chehab- Segment Information Table (SIT)
49889272ca1SMauro Carvalho Chehab   It contains segment information such as valid block count and bitmap for the
49989272ca1SMauro Carvalho Chehab   validity of all the blocks.
50089272ca1SMauro Carvalho Chehab
50189272ca1SMauro Carvalho Chehab- Node Address Table (NAT)
50289272ca1SMauro Carvalho Chehab   It is composed of a block address table for all the node blocks stored in
50389272ca1SMauro Carvalho Chehab   Main area.
50489272ca1SMauro Carvalho Chehab
50589272ca1SMauro Carvalho Chehab- Segment Summary Area (SSA)
50689272ca1SMauro Carvalho Chehab   It contains summary entries which contains the owner information of all the
50789272ca1SMauro Carvalho Chehab   data and node blocks stored in Main area.
50889272ca1SMauro Carvalho Chehab
50989272ca1SMauro Carvalho Chehab- Main Area
51089272ca1SMauro Carvalho Chehab   It contains file and directory data including their indices.
51189272ca1SMauro Carvalho Chehab
51289272ca1SMauro Carvalho ChehabIn order to avoid misalignment between file system and flash-based storage, F2FS
51389272ca1SMauro Carvalho Chehabaligns the start block address of CP with the segment size. Also, it aligns the
51489272ca1SMauro Carvalho Chehabstart block address of Main area with the zone size by reserving some segments
51589272ca1SMauro Carvalho Chehabin SSA area.
51689272ca1SMauro Carvalho Chehab
51789272ca1SMauro Carvalho ChehabReference the following survey for additional technical details.
51889272ca1SMauro Carvalho Chehabhttps://wiki.linaro.org/WorkingGroups/Kernel/Projects/FlashCardSurvey
51989272ca1SMauro Carvalho Chehab
52089272ca1SMauro Carvalho ChehabFile System Metadata Structure
52189272ca1SMauro Carvalho Chehab------------------------------
52289272ca1SMauro Carvalho Chehab
52389272ca1SMauro Carvalho ChehabF2FS adopts the checkpointing scheme to maintain file system consistency. At
52489272ca1SMauro Carvalho Chehabmount time, F2FS first tries to find the last valid checkpoint data by scanning
52589272ca1SMauro Carvalho ChehabCP area. In order to reduce the scanning time, F2FS uses only two copies of CP.
52689272ca1SMauro Carvalho ChehabOne of them always indicates the last valid data, which is called as shadow copy
52789272ca1SMauro Carvalho Chehabmechanism. In addition to CP, NAT and SIT also adopt the shadow copy mechanism.
52889272ca1SMauro Carvalho Chehab
52989272ca1SMauro Carvalho ChehabFor file system consistency, each CP points to which NAT and SIT copies are
53089272ca1SMauro Carvalho Chehabvalid, as shown as below::
53189272ca1SMauro Carvalho Chehab
53289272ca1SMauro Carvalho Chehab  +--------+----------+---------+
53389272ca1SMauro Carvalho Chehab  |   CP   |    SIT   |   NAT   |
53489272ca1SMauro Carvalho Chehab  +--------+----------+---------+
53589272ca1SMauro Carvalho Chehab  .         .          .          .
53689272ca1SMauro Carvalho Chehab  .            .              .              .
53789272ca1SMauro Carvalho Chehab  .               .                 .                 .
53889272ca1SMauro Carvalho Chehab  +-------+-------+--------+--------+--------+--------+
53989272ca1SMauro Carvalho Chehab  | CP #0 | CP #1 | SIT #0 | SIT #1 | NAT #0 | NAT #1 |
54089272ca1SMauro Carvalho Chehab  +-------+-------+--------+--------+--------+--------+
54189272ca1SMauro Carvalho Chehab     |             ^                          ^
54289272ca1SMauro Carvalho Chehab     |             |                          |
54389272ca1SMauro Carvalho Chehab     `----------------------------------------'
54489272ca1SMauro Carvalho Chehab
54589272ca1SMauro Carvalho ChehabIndex Structure
54689272ca1SMauro Carvalho Chehab---------------
54789272ca1SMauro Carvalho Chehab
54889272ca1SMauro Carvalho ChehabThe key data structure to manage the data locations is a "node". Similar to
54989272ca1SMauro Carvalho Chehabtraditional file structures, F2FS has three types of node: inode, direct node,
55089272ca1SMauro Carvalho Chehabindirect node. F2FS assigns 4KB to an inode block which contains 923 data block
55189272ca1SMauro Carvalho Chehabindices, two direct node pointers, two indirect node pointers, and one double
55289272ca1SMauro Carvalho Chehabindirect node pointer as described below. One direct node block contains 1018
55389272ca1SMauro Carvalho Chehabdata blocks, and one indirect node block contains also 1018 node blocks. Thus,
55489272ca1SMauro Carvalho Chehabone inode block (i.e., a file) covers::
55589272ca1SMauro Carvalho Chehab
55689272ca1SMauro Carvalho Chehab  4KB * (923 + 2 * 1018 + 2 * 1018 * 1018 + 1018 * 1018 * 1018) := 3.94TB.
55789272ca1SMauro Carvalho Chehab
55889272ca1SMauro Carvalho Chehab   Inode block (4KB)
55989272ca1SMauro Carvalho Chehab     |- data (923)
56089272ca1SMauro Carvalho Chehab     |- direct node (2)
56189272ca1SMauro Carvalho Chehab     |          `- data (1018)
56289272ca1SMauro Carvalho Chehab     |- indirect node (2)
56389272ca1SMauro Carvalho Chehab     |            `- direct node (1018)
56489272ca1SMauro Carvalho Chehab     |                       `- data (1018)
56589272ca1SMauro Carvalho Chehab     `- double indirect node (1)
56689272ca1SMauro Carvalho Chehab                         `- indirect node (1018)
56789272ca1SMauro Carvalho Chehab			              `- direct node (1018)
56889272ca1SMauro Carvalho Chehab	                                         `- data (1018)
56989272ca1SMauro Carvalho Chehab
570ca313c82SRandy DunlapNote that all the node blocks are mapped by NAT which means the location of
57189272ca1SMauro Carvalho Chehabeach node is translated by the NAT table. In the consideration of the wandering
57289272ca1SMauro Carvalho Chehabtree problem, F2FS is able to cut off the propagation of node updates caused by
57389272ca1SMauro Carvalho Chehableaf data writes.
57489272ca1SMauro Carvalho Chehab
57589272ca1SMauro Carvalho ChehabDirectory Structure
57689272ca1SMauro Carvalho Chehab-------------------
57789272ca1SMauro Carvalho Chehab
57889272ca1SMauro Carvalho ChehabA directory entry occupies 11 bytes, which consists of the following attributes.
57989272ca1SMauro Carvalho Chehab
58089272ca1SMauro Carvalho Chehab- hash		hash value of the file name
58189272ca1SMauro Carvalho Chehab- ino		inode number
58289272ca1SMauro Carvalho Chehab- len		the length of file name
58389272ca1SMauro Carvalho Chehab- type		file type such as directory, symlink, etc
58489272ca1SMauro Carvalho Chehab
58589272ca1SMauro Carvalho ChehabA dentry block consists of 214 dentry slots and file names. Therein a bitmap is
58689272ca1SMauro Carvalho Chehabused to represent whether each dentry is valid or not. A dentry block occupies
58789272ca1SMauro Carvalho Chehab4KB with the following composition.
58889272ca1SMauro Carvalho Chehab
58989272ca1SMauro Carvalho Chehab::
59089272ca1SMauro Carvalho Chehab
59189272ca1SMauro Carvalho Chehab  Dentry Block(4 K) = bitmap (27 bytes) + reserved (3 bytes) +
59289272ca1SMauro Carvalho Chehab	              dentries(11 * 214 bytes) + file name (8 * 214 bytes)
59389272ca1SMauro Carvalho Chehab
59489272ca1SMauro Carvalho Chehab                         [Bucket]
59589272ca1SMauro Carvalho Chehab             +--------------------------------+
59689272ca1SMauro Carvalho Chehab             |dentry block 1 | dentry block 2 |
59789272ca1SMauro Carvalho Chehab             +--------------------------------+
59889272ca1SMauro Carvalho Chehab             .               .
59989272ca1SMauro Carvalho Chehab       .                             .
60089272ca1SMauro Carvalho Chehab  .       [Dentry Block Structure: 4KB]       .
60189272ca1SMauro Carvalho Chehab  +--------+----------+----------+------------+
60289272ca1SMauro Carvalho Chehab  | bitmap | reserved | dentries | file names |
60389272ca1SMauro Carvalho Chehab  +--------+----------+----------+------------+
60489272ca1SMauro Carvalho Chehab  [Dentry Block: 4KB] .   .
60589272ca1SMauro Carvalho Chehab		 .               .
60689272ca1SMauro Carvalho Chehab            .                          .
60789272ca1SMauro Carvalho Chehab            +------+------+-----+------+
60889272ca1SMauro Carvalho Chehab            | hash | ino  | len | type |
60989272ca1SMauro Carvalho Chehab            +------+------+-----+------+
61089272ca1SMauro Carvalho Chehab            [Dentry Structure: 11 bytes]
61189272ca1SMauro Carvalho Chehab
61289272ca1SMauro Carvalho ChehabF2FS implements multi-level hash tables for directory structure. Each level has
61389272ca1SMauro Carvalho Chehaba hash table with dedicated number of hash buckets as shown below. Note that
61489272ca1SMauro Carvalho Chehab"A(2B)" means a bucket includes 2 data blocks.
61589272ca1SMauro Carvalho Chehab
61689272ca1SMauro Carvalho Chehab::
61789272ca1SMauro Carvalho Chehab
61889272ca1SMauro Carvalho Chehab    ----------------------
61989272ca1SMauro Carvalho Chehab    A : bucket
62089272ca1SMauro Carvalho Chehab    B : block
62189272ca1SMauro Carvalho Chehab    N : MAX_DIR_HASH_DEPTH
62289272ca1SMauro Carvalho Chehab    ----------------------
62389272ca1SMauro Carvalho Chehab
62489272ca1SMauro Carvalho Chehab    level #0   | A(2B)
62589272ca1SMauro Carvalho Chehab	    |
62689272ca1SMauro Carvalho Chehab    level #1   | A(2B) - A(2B)
62789272ca1SMauro Carvalho Chehab	    |
62889272ca1SMauro Carvalho Chehab    level #2   | A(2B) - A(2B) - A(2B) - A(2B)
62989272ca1SMauro Carvalho Chehab	.     |   .       .       .       .
63089272ca1SMauro Carvalho Chehab    level #N/2 | A(2B) - A(2B) - A(2B) - A(2B) - A(2B) - ... - A(2B)
63189272ca1SMauro Carvalho Chehab	.     |   .       .       .       .
63289272ca1SMauro Carvalho Chehab    level #N   | A(4B) - A(4B) - A(4B) - A(4B) - A(4B) - ... - A(4B)
63389272ca1SMauro Carvalho Chehab
63489272ca1SMauro Carvalho ChehabThe number of blocks and buckets are determined by::
63589272ca1SMauro Carvalho Chehab
63689272ca1SMauro Carvalho Chehab                            ,- 2, if n < MAX_DIR_HASH_DEPTH / 2,
63789272ca1SMauro Carvalho Chehab  # of blocks in level #n = |
63889272ca1SMauro Carvalho Chehab                            `- 4, Otherwise
63989272ca1SMauro Carvalho Chehab
64089272ca1SMauro Carvalho Chehab                             ,- 2^(n + dir_level),
64189272ca1SMauro Carvalho Chehab			     |        if n + dir_level < MAX_DIR_HASH_DEPTH / 2,
64289272ca1SMauro Carvalho Chehab  # of buckets in level #n = |
64389272ca1SMauro Carvalho Chehab                             `- 2^((MAX_DIR_HASH_DEPTH / 2) - 1),
64489272ca1SMauro Carvalho Chehab			              Otherwise
64589272ca1SMauro Carvalho Chehab
64689272ca1SMauro Carvalho ChehabWhen F2FS finds a file name in a directory, at first a hash value of the file
64789272ca1SMauro Carvalho Chehabname is calculated. Then, F2FS scans the hash table in level #0 to find the
64889272ca1SMauro Carvalho Chehabdentry consisting of the file name and its inode number. If not found, F2FS
64989272ca1SMauro Carvalho Chehabscans the next hash table in level #1. In this way, F2FS scans hash tables in
650ca313c82SRandy Dunlapeach levels incrementally from 1 to N. In each level F2FS needs to scan only
65189272ca1SMauro Carvalho Chehabone bucket determined by the following equation, which shows O(log(# of files))
65289272ca1SMauro Carvalho Chehabcomplexity::
65389272ca1SMauro Carvalho Chehab
65489272ca1SMauro Carvalho Chehab  bucket number to scan in level #n = (hash value) % (# of buckets in level #n)
65589272ca1SMauro Carvalho Chehab
65689272ca1SMauro Carvalho ChehabIn the case of file creation, F2FS finds empty consecutive slots that cover the
65789272ca1SMauro Carvalho Chehabfile name. F2FS searches the empty slots in the hash tables of whole levels from
65889272ca1SMauro Carvalho Chehab1 to N in the same way as the lookup operation.
65989272ca1SMauro Carvalho Chehab
66089272ca1SMauro Carvalho ChehabThe following figure shows an example of two cases holding children::
66189272ca1SMauro Carvalho Chehab
66289272ca1SMauro Carvalho Chehab       --------------> Dir <--------------
66389272ca1SMauro Carvalho Chehab       |                                 |
66489272ca1SMauro Carvalho Chehab    child                             child
66589272ca1SMauro Carvalho Chehab
66689272ca1SMauro Carvalho Chehab    child - child                     [hole] - child
66789272ca1SMauro Carvalho Chehab
66889272ca1SMauro Carvalho Chehab    child - child - child             [hole] - [hole] - child
66989272ca1SMauro Carvalho Chehab
67089272ca1SMauro Carvalho Chehab   Case 1:                           Case 2:
67189272ca1SMauro Carvalho Chehab   Number of children = 6,           Number of children = 3,
67289272ca1SMauro Carvalho Chehab   File size = 7                     File size = 7
67389272ca1SMauro Carvalho Chehab
67489272ca1SMauro Carvalho ChehabDefault Block Allocation
67589272ca1SMauro Carvalho Chehab------------------------
67689272ca1SMauro Carvalho Chehab
67789272ca1SMauro Carvalho ChehabAt runtime, F2FS manages six active logs inside "Main" area: Hot/Warm/Cold node
67889272ca1SMauro Carvalho Chehaband Hot/Warm/Cold data.
67989272ca1SMauro Carvalho Chehab
68089272ca1SMauro Carvalho Chehab- Hot node	contains direct node blocks of directories.
68189272ca1SMauro Carvalho Chehab- Warm node	contains direct node blocks except hot node blocks.
68289272ca1SMauro Carvalho Chehab- Cold node	contains indirect node blocks
68389272ca1SMauro Carvalho Chehab- Hot data	contains dentry blocks
68489272ca1SMauro Carvalho Chehab- Warm data	contains data blocks except hot and cold data blocks
68589272ca1SMauro Carvalho Chehab- Cold data	contains multimedia data or migrated data blocks
68689272ca1SMauro Carvalho Chehab
68789272ca1SMauro Carvalho ChehabLFS has two schemes for free space management: threaded log and copy-and-compac-
68889272ca1SMauro Carvalho Chehabtion. The copy-and-compaction scheme which is known as cleaning, is well-suited
68989272ca1SMauro Carvalho Chehabfor devices showing very good sequential write performance, since free segments
69089272ca1SMauro Carvalho Chehabare served all the time for writing new data. However, it suffers from cleaning
69189272ca1SMauro Carvalho Chehaboverhead under high utilization. Contrarily, the threaded log scheme suffers
69289272ca1SMauro Carvalho Chehabfrom random writes, but no cleaning process is needed. F2FS adopts a hybrid
69389272ca1SMauro Carvalho Chehabscheme where the copy-and-compaction scheme is adopted by default, but the
69489272ca1SMauro Carvalho Chehabpolicy is dynamically changed to the threaded log scheme according to the file
69589272ca1SMauro Carvalho Chehabsystem status.
69689272ca1SMauro Carvalho Chehab
69789272ca1SMauro Carvalho ChehabIn order to align F2FS with underlying flash-based storage, F2FS allocates a
69889272ca1SMauro Carvalho Chehabsegment in a unit of section. F2FS expects that the section size would be the
69989272ca1SMauro Carvalho Chehabsame as the unit size of garbage collection in FTL. Furthermore, with respect
70089272ca1SMauro Carvalho Chehabto the mapping granularity in FTL, F2FS allocates each section of the active
70189272ca1SMauro Carvalho Chehablogs from different zones as much as possible, since FTL can write the data in
70289272ca1SMauro Carvalho Chehabthe active logs into one allocation unit according to its mapping granularity.
70389272ca1SMauro Carvalho Chehab
70489272ca1SMauro Carvalho ChehabCleaning process
70589272ca1SMauro Carvalho Chehab----------------
70689272ca1SMauro Carvalho Chehab
70789272ca1SMauro Carvalho ChehabF2FS does cleaning both on demand and in the background. On-demand cleaning is
70889272ca1SMauro Carvalho Chehabtriggered when there are not enough free segments to serve VFS calls. Background
70989272ca1SMauro Carvalho Chehabcleaner is operated by a kernel thread, and triggers the cleaning job when the
71089272ca1SMauro Carvalho Chehabsystem is idle.
71189272ca1SMauro Carvalho Chehab
71289272ca1SMauro Carvalho ChehabF2FS supports two victim selection policies: greedy and cost-benefit algorithms.
71389272ca1SMauro Carvalho ChehabIn the greedy algorithm, F2FS selects a victim segment having the smallest number
71489272ca1SMauro Carvalho Chehabof valid blocks. In the cost-benefit algorithm, F2FS selects a victim segment
71589272ca1SMauro Carvalho Chehabaccording to the segment age and the number of valid blocks in order to address
71689272ca1SMauro Carvalho Chehablog block thrashing problem in the greedy algorithm. F2FS adopts the greedy
71789272ca1SMauro Carvalho Chehabalgorithm for on-demand cleaner, while background cleaner adopts cost-benefit
71889272ca1SMauro Carvalho Chehabalgorithm.
71989272ca1SMauro Carvalho Chehab
72089272ca1SMauro Carvalho ChehabIn order to identify whether the data in the victim segment are valid or not,
72189272ca1SMauro Carvalho ChehabF2FS manages a bitmap. Each bit represents the validity of a block, and the
72289272ca1SMauro Carvalho Chehabbitmap is composed of a bit stream covering whole blocks in main area.
72389272ca1SMauro Carvalho Chehab
72489272ca1SMauro Carvalho ChehabWrite-hint Policy
72589272ca1SMauro Carvalho Chehab-----------------
72689272ca1SMauro Carvalho Chehab
72789272ca1SMauro Carvalho Chehab1) whint_mode=off. F2FS only passes down WRITE_LIFE_NOT_SET.
72889272ca1SMauro Carvalho Chehab
72989272ca1SMauro Carvalho Chehab2) whint_mode=user-based. F2FS tries to pass down hints given by
73089272ca1SMauro Carvalho Chehabusers.
73189272ca1SMauro Carvalho Chehab
73289272ca1SMauro Carvalho Chehab===================== ======================== ===================
73389272ca1SMauro Carvalho ChehabUser                  F2FS                     Block
73489272ca1SMauro Carvalho Chehab===================== ======================== ===================
7353c16dc40SChao YuN/A                   META                     WRITE_LIFE_NOT_SET
7363c16dc40SChao YuN/A                   HOT_NODE                 "
7373c16dc40SChao YuN/A                   WARM_NODE                "
7383c16dc40SChao YuN/A                   COLD_NODE                "
73989272ca1SMauro Carvalho Chehabioctl(COLD)           COLD_DATA                WRITE_LIFE_EXTREME
74089272ca1SMauro Carvalho Chehabextension list        "                        "
74189272ca1SMauro Carvalho Chehab
74289272ca1SMauro Carvalho Chehab-- buffered io
74389272ca1SMauro Carvalho ChehabWRITE_LIFE_EXTREME    COLD_DATA                WRITE_LIFE_EXTREME
74489272ca1SMauro Carvalho ChehabWRITE_LIFE_SHORT      HOT_DATA                 WRITE_LIFE_SHORT
74589272ca1SMauro Carvalho ChehabWRITE_LIFE_NOT_SET    WARM_DATA                WRITE_LIFE_NOT_SET
74689272ca1SMauro Carvalho ChehabWRITE_LIFE_NONE       "                        "
74789272ca1SMauro Carvalho ChehabWRITE_LIFE_MEDIUM     "                        "
74889272ca1SMauro Carvalho ChehabWRITE_LIFE_LONG       "                        "
74989272ca1SMauro Carvalho Chehab
75089272ca1SMauro Carvalho Chehab-- direct io
75189272ca1SMauro Carvalho ChehabWRITE_LIFE_EXTREME    COLD_DATA                WRITE_LIFE_EXTREME
75289272ca1SMauro Carvalho ChehabWRITE_LIFE_SHORT      HOT_DATA                 WRITE_LIFE_SHORT
75389272ca1SMauro Carvalho ChehabWRITE_LIFE_NOT_SET    WARM_DATA                WRITE_LIFE_NOT_SET
75489272ca1SMauro Carvalho ChehabWRITE_LIFE_NONE       "                        WRITE_LIFE_NONE
75589272ca1SMauro Carvalho ChehabWRITE_LIFE_MEDIUM     "                        WRITE_LIFE_MEDIUM
75689272ca1SMauro Carvalho ChehabWRITE_LIFE_LONG       "                        WRITE_LIFE_LONG
75789272ca1SMauro Carvalho Chehab===================== ======================== ===================
75889272ca1SMauro Carvalho Chehab
75989272ca1SMauro Carvalho Chehab3) whint_mode=fs-based. F2FS passes down hints with its policy.
76089272ca1SMauro Carvalho Chehab
76189272ca1SMauro Carvalho Chehab===================== ======================== ===================
76289272ca1SMauro Carvalho ChehabUser                  F2FS                     Block
76389272ca1SMauro Carvalho Chehab===================== ======================== ===================
7643c16dc40SChao YuN/A                   META                     WRITE_LIFE_MEDIUM;
7653c16dc40SChao YuN/A                   HOT_NODE                 WRITE_LIFE_NOT_SET
7663c16dc40SChao YuN/A                   WARM_NODE                "
7673c16dc40SChao YuN/A                   COLD_NODE                WRITE_LIFE_NONE
76889272ca1SMauro Carvalho Chehabioctl(COLD)           COLD_DATA                WRITE_LIFE_EXTREME
76989272ca1SMauro Carvalho Chehabextension list        "                        "
77089272ca1SMauro Carvalho Chehab
77189272ca1SMauro Carvalho Chehab-- buffered io
77289272ca1SMauro Carvalho ChehabWRITE_LIFE_EXTREME    COLD_DATA                WRITE_LIFE_EXTREME
77389272ca1SMauro Carvalho ChehabWRITE_LIFE_SHORT      HOT_DATA                 WRITE_LIFE_SHORT
77489272ca1SMauro Carvalho ChehabWRITE_LIFE_NOT_SET    WARM_DATA                WRITE_LIFE_LONG
77589272ca1SMauro Carvalho ChehabWRITE_LIFE_NONE       "                        "
77689272ca1SMauro Carvalho ChehabWRITE_LIFE_MEDIUM     "                        "
77789272ca1SMauro Carvalho ChehabWRITE_LIFE_LONG       "                        "
77889272ca1SMauro Carvalho Chehab
77989272ca1SMauro Carvalho Chehab-- direct io
78089272ca1SMauro Carvalho ChehabWRITE_LIFE_EXTREME    COLD_DATA                WRITE_LIFE_EXTREME
78189272ca1SMauro Carvalho ChehabWRITE_LIFE_SHORT      HOT_DATA                 WRITE_LIFE_SHORT
78289272ca1SMauro Carvalho ChehabWRITE_LIFE_NOT_SET    WARM_DATA                WRITE_LIFE_NOT_SET
78389272ca1SMauro Carvalho ChehabWRITE_LIFE_NONE       "                        WRITE_LIFE_NONE
78489272ca1SMauro Carvalho ChehabWRITE_LIFE_MEDIUM     "                        WRITE_LIFE_MEDIUM
78589272ca1SMauro Carvalho ChehabWRITE_LIFE_LONG       "                        WRITE_LIFE_LONG
78689272ca1SMauro Carvalho Chehab===================== ======================== ===================
78789272ca1SMauro Carvalho Chehab
78889272ca1SMauro Carvalho ChehabFallocate(2) Policy
78989272ca1SMauro Carvalho Chehab-------------------
79089272ca1SMauro Carvalho Chehab
791ca313c82SRandy DunlapThe default policy follows the below POSIX rule.
79289272ca1SMauro Carvalho Chehab
79389272ca1SMauro Carvalho ChehabAllocating disk space
79489272ca1SMauro Carvalho Chehab    The default operation (i.e., mode is zero) of fallocate() allocates
79589272ca1SMauro Carvalho Chehab    the disk space within the range specified by offset and len.  The
79689272ca1SMauro Carvalho Chehab    file size (as reported by stat(2)) will be changed if offset+len is
79789272ca1SMauro Carvalho Chehab    greater than the file size.  Any subregion within the range specified
79889272ca1SMauro Carvalho Chehab    by offset and len that did not contain data before the call will be
79989272ca1SMauro Carvalho Chehab    initialized to zero.  This default behavior closely resembles the
80089272ca1SMauro Carvalho Chehab    behavior of the posix_fallocate(3) library function, and is intended
80189272ca1SMauro Carvalho Chehab    as a method of optimally implementing that function.
80289272ca1SMauro Carvalho Chehab
80389272ca1SMauro Carvalho ChehabHowever, once F2FS receives ioctl(fd, F2FS_IOC_SET_PIN_FILE) in prior to
804ca313c82SRandy Dunlapfallocate(fd, DEFAULT_MODE), it allocates on-disk block addressess having
80589272ca1SMauro Carvalho Chehabzero or random data, which is useful to the below scenario where:
80689272ca1SMauro Carvalho Chehab
80789272ca1SMauro Carvalho Chehab 1. create(fd)
80889272ca1SMauro Carvalho Chehab 2. ioctl(fd, F2FS_IOC_SET_PIN_FILE)
80989272ca1SMauro Carvalho Chehab 3. fallocate(fd, 0, 0, size)
81089272ca1SMauro Carvalho Chehab 4. address = fibmap(fd, offset)
81189272ca1SMauro Carvalho Chehab 5. open(blkdev)
81289272ca1SMauro Carvalho Chehab 6. write(blkdev, address)
81389272ca1SMauro Carvalho Chehab
81489272ca1SMauro Carvalho ChehabCompression implementation
81589272ca1SMauro Carvalho Chehab--------------------------
81689272ca1SMauro Carvalho Chehab
81789272ca1SMauro Carvalho Chehab- New term named cluster is defined as basic unit of compression, file can
81889272ca1SMauro Carvalho Chehab  be divided into multiple clusters logically. One cluster includes 4 << n
81989272ca1SMauro Carvalho Chehab  (n >= 0) logical pages, compression size is also cluster size, each of
82089272ca1SMauro Carvalho Chehab  cluster can be compressed or not.
82189272ca1SMauro Carvalho Chehab
82289272ca1SMauro Carvalho Chehab- In cluster metadata layout, one special block address is used to indicate
823ca313c82SRandy Dunlap  a cluster is a compressed one or normal one; for compressed cluster, following
82489272ca1SMauro Carvalho Chehab  metadata maps cluster to [1, 4 << n - 1] physical blocks, in where f2fs
82589272ca1SMauro Carvalho Chehab  stores data including compress header and compressed data.
82689272ca1SMauro Carvalho Chehab
82789272ca1SMauro Carvalho Chehab- In order to eliminate write amplification during overwrite, F2FS only
82889272ca1SMauro Carvalho Chehab  support compression on write-once file, data can be compressed only when
8294fc781a3SChao Yu  all logical blocks in cluster contain valid data and compress ratio of
8304fc781a3SChao Yu  cluster data is lower than specified threshold.
83189272ca1SMauro Carvalho Chehab
832*151b1982SFengnan Chang- To enable compression on regular inode, there are four ways:
83389272ca1SMauro Carvalho Chehab
83489272ca1SMauro Carvalho Chehab  * chattr +c file
83589272ca1SMauro Carvalho Chehab  * chattr +c dir; touch dir/file
83689272ca1SMauro Carvalho Chehab  * mount w/ -o compress_extension=ext; touch file.ext
83738740707SChao Yu  * mount w/ -o compress_extension=*; touch any_file
83838740707SChao Yu
839*151b1982SFengnan Chang- To disable compression on regular inode, there are two ways:
840*151b1982SFengnan Chang
841*151b1982SFengnan Chang  * chattr -c file
842*151b1982SFengnan Chang  * mount w/ -o nocompress_extension=ext; touch file.ext
843*151b1982SFengnan Chang
844*151b1982SFengnan Chang- Priority in between FS_COMPR_FL, FS_NOCOMP_FS, extensions:
845*151b1982SFengnan Chang
846*151b1982SFengnan Chang  * compress_extension=so; nocompress_extension=zip; chattr +c dir; touch
847*151b1982SFengnan Chang    dir/foo.so; touch dir/bar.zip; touch dir/baz.txt; then foo.so and baz.txt
848*151b1982SFengnan Chang    should be compresse, bar.zip should be non-compressed. chattr +c dir/bar.zip
849*151b1982SFengnan Chang    can enable compress on bar.zip.
850*151b1982SFengnan Chang  * compress_extension=so; nocompress_extension=zip; chattr -c dir; touch
851*151b1982SFengnan Chang    dir/foo.so; touch dir/bar.zip; touch dir/baz.txt; then foo.so should be
852*151b1982SFengnan Chang    compresse, bar.zip and baz.txt should be non-compressed.
853*151b1982SFengnan Chang    chattr+c dir/bar.zip; chattr+c dir/baz.txt; can enable compress on bar.zip
854*151b1982SFengnan Chang    and baz.txt.
855*151b1982SFengnan Chang
85638740707SChao Yu- At this point, compression feature doesn't expose compressed space to user
85738740707SChao Yu  directly in order to guarantee potential data updates later to the space.
85838740707SChao Yu  Instead, the main goal is to reduce data writes to flash disk as much as
85938740707SChao Yu  possible, resulting in extending disk life time as well as relaxing IO
86038740707SChao Yu  congestion. Alternatively, we've added ioctl interface to reclaim compressed
86138740707SChao Yu  space and show it to user after putting the immutable bit.
86289272ca1SMauro Carvalho Chehab
86389272ca1SMauro Carvalho ChehabCompress metadata layout::
86489272ca1SMauro Carvalho Chehab
86589272ca1SMauro Carvalho Chehab				[Dnode Structure]
86689272ca1SMauro Carvalho Chehab		+-----------------------------------------------+
86789272ca1SMauro Carvalho Chehab		| cluster 1 | cluster 2 | ......... | cluster N |
86889272ca1SMauro Carvalho Chehab		+-----------------------------------------------+
86989272ca1SMauro Carvalho Chehab		.           .                       .           .
87089272ca1SMauro Carvalho Chehab	.                       .                .                      .
87189272ca1SMauro Carvalho Chehab    .         Compressed Cluster       .        .        Normal Cluster            .
87289272ca1SMauro Carvalho Chehab    +----------+---------+---------+---------+  +---------+---------+---------+---------+
87389272ca1SMauro Carvalho Chehab    |compr flag| block 1 | block 2 | block 3 |  | block 1 | block 2 | block 3 | block 4 |
87489272ca1SMauro Carvalho Chehab    +----------+---------+---------+---------+  +---------+---------+---------+---------+
87589272ca1SMauro Carvalho Chehab	    .                             .
87689272ca1SMauro Carvalho Chehab	    .                                           .
87789272ca1SMauro Carvalho Chehab	.                                                           .
87889272ca1SMauro Carvalho Chehab	+-------------+-------------+----------+----------------------------+
87989272ca1SMauro Carvalho Chehab	| data length | data chksum | reserved |      compressed data       |
88089272ca1SMauro Carvalho Chehab	+-------------+-------------+----------+----------------------------+
881de881df9SAravind Ramesh
882602a16d5SDaeho JeongCompression mode
883602a16d5SDaeho Jeong--------------------------
884602a16d5SDaeho Jeong
885602a16d5SDaeho Jeongf2fs supports "fs" and "user" compression modes with "compression_mode" mount option.
886602a16d5SDaeho JeongWith this option, f2fs provides a choice to select the way how to compress the
887602a16d5SDaeho Jeongcompression enabled files (refer to "Compression implementation" section for how to
888602a16d5SDaeho Jeongenable compression on a regular inode).
889602a16d5SDaeho Jeong
890602a16d5SDaeho Jeong1) compress_mode=fs
891602a16d5SDaeho JeongThis is the default option. f2fs does automatic compression in the writeback of the
892602a16d5SDaeho Jeongcompression enabled files.
893602a16d5SDaeho Jeong
894602a16d5SDaeho Jeong2) compress_mode=user
895092af2ebSEd TsaiThis disables the automatic compression and gives the user discretion of choosing the
896602a16d5SDaeho Jeongtarget file and the timing. The user can do manual compression/decompression on the
897602a16d5SDaeho Jeongcompression enabled files using F2FS_IOC_DECOMPRESS_FILE and F2FS_IOC_COMPRESS_FILE
898602a16d5SDaeho Jeongioctls like the below.
899602a16d5SDaeho Jeong
900602a16d5SDaeho JeongTo decompress a file,
901602a16d5SDaeho Jeong
902602a16d5SDaeho Jeongfd = open(filename, O_WRONLY, 0);
903602a16d5SDaeho Jeongret = ioctl(fd, F2FS_IOC_DECOMPRESS_FILE);
904602a16d5SDaeho Jeong
905602a16d5SDaeho JeongTo compress a file,
906602a16d5SDaeho Jeong
907602a16d5SDaeho Jeongfd = open(filename, O_WRONLY, 0);
908602a16d5SDaeho Jeongret = ioctl(fd, F2FS_IOC_COMPRESS_FILE);
909602a16d5SDaeho Jeong
910de881df9SAravind RameshNVMe Zoned Namespace devices
911de881df9SAravind Ramesh----------------------------
912de881df9SAravind Ramesh
913de881df9SAravind Ramesh- ZNS defines a per-zone capacity which can be equal or less than the
914de881df9SAravind Ramesh  zone-size. Zone-capacity is the number of usable blocks in the zone.
915ca313c82SRandy Dunlap  F2FS checks if zone-capacity is less than zone-size, if it is, then any
916de881df9SAravind Ramesh  segment which starts after the zone-capacity is marked as not-free in
917de881df9SAravind Ramesh  the free segment bitmap at initial mount time. These segments are marked
918de881df9SAravind Ramesh  as permanently used so they are not allocated for writes and
919de881df9SAravind Ramesh  consequently are not needed to be garbage collected. In case the
920de881df9SAravind Ramesh  zone-capacity is not aligned to default segment size(2MB), then a segment
921de881df9SAravind Ramesh  can start before the zone-capacity and span across zone-capacity boundary.
922de881df9SAravind Ramesh  Such spanning segments are also considered as usable segments. All blocks
923de881df9SAravind Ramesh  past the zone-capacity are considered unusable in these segments.
924