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. 11389272ca1SMauro Carvalho Chehabdisable_roll_forward Disable the roll-forward recovery routine 11489272ca1SMauro Carvalho Chehabnorecovery Disable the roll-forward recovery routine, mounted read- 11589272ca1SMauro Carvalho Chehab only (i.e., -o ro,disable_roll_forward) 11689272ca1SMauro Carvalho Chehabdiscard/nodiscard Enable/disable real-time discard in f2fs, if discard is 11789272ca1SMauro Carvalho Chehab enabled, f2fs will issue discard/TRIM commands when a 11889272ca1SMauro Carvalho Chehab segment is cleaned. 11989272ca1SMauro Carvalho Chehabno_heap Disable heap-style segment allocation which finds free 12089272ca1SMauro Carvalho Chehab segments for data from the beginning of main area, while 12189272ca1SMauro Carvalho Chehab for node from the end of main area. 12289272ca1SMauro Carvalho Chehabnouser_xattr Disable Extended User Attributes. Note: xattr is enabled 12389272ca1SMauro Carvalho Chehab by default if CONFIG_F2FS_FS_XATTR is selected. 12489272ca1SMauro Carvalho Chehabnoacl Disable POSIX Access Control List. Note: acl is enabled 12589272ca1SMauro Carvalho Chehab by default if CONFIG_F2FS_FS_POSIX_ACL is selected. 12689272ca1SMauro Carvalho Chehabactive_logs=%u Support configuring the number of active logs. In the 12789272ca1SMauro Carvalho Chehab current design, f2fs supports only 2, 4, and 6 logs. 12889272ca1SMauro Carvalho Chehab Default number is 6. 12989272ca1SMauro Carvalho Chehabdisable_ext_identify Disable the extension list configured by mkfs, so f2fs 13089272ca1SMauro Carvalho Chehab does not aware of cold files such as media files. 13189272ca1SMauro Carvalho Chehabinline_xattr Enable the inline xattrs feature. 13289272ca1SMauro Carvalho Chehabnoinline_xattr Disable the inline xattrs feature. 13389272ca1SMauro Carvalho Chehabinline_xattr_size=%u Support configuring inline xattr size, it depends on 13489272ca1SMauro Carvalho Chehab flexible inline xattr feature. 13589272ca1SMauro Carvalho Chehabinline_data Enable the inline data feature: New created small(<~3.4k) 13689272ca1SMauro Carvalho Chehab files can be written into inode block. 13789272ca1SMauro Carvalho Chehabinline_dentry Enable the inline dir feature: data in new created 13889272ca1SMauro Carvalho Chehab directory entries can be written into inode block. The 13989272ca1SMauro Carvalho Chehab space of inode block which is used to store inline 14089272ca1SMauro Carvalho Chehab dentries is limited to ~3.4k. 14189272ca1SMauro Carvalho Chehabnoinline_dentry Disable the inline dentry feature. 14289272ca1SMauro Carvalho Chehabflush_merge Merge concurrent cache_flush commands as much as possible 14389272ca1SMauro Carvalho Chehab to eliminate redundant command issues. If the underlying 14489272ca1SMauro Carvalho Chehab device handles the cache_flush command relatively slowly, 14589272ca1SMauro Carvalho Chehab recommend to enable this option. 14689272ca1SMauro Carvalho Chehabnobarrier This option can be used if underlying storage guarantees 14789272ca1SMauro Carvalho Chehab its cached data should be written to the novolatile area. 14889272ca1SMauro Carvalho Chehab If this option is set, no cache_flush commands are issued 14989272ca1SMauro Carvalho Chehab but f2fs still guarantees the write ordering of all the 15089272ca1SMauro Carvalho Chehab data writes. 15189272ca1SMauro Carvalho Chehabfastboot This option is used when a system wants to reduce mount 15289272ca1SMauro Carvalho Chehab time as much as possible, even though normal performance 15389272ca1SMauro Carvalho Chehab can be sacrificed. 15489272ca1SMauro Carvalho Chehabextent_cache Enable an extent cache based on rb-tree, it can cache 15589272ca1SMauro Carvalho Chehab as many as extent which map between contiguous logical 15689272ca1SMauro Carvalho Chehab address and physical address per inode, resulting in 15789272ca1SMauro Carvalho Chehab increasing the cache hit ratio. Set by default. 15889272ca1SMauro Carvalho Chehabnoextent_cache Disable an extent cache based on rb-tree explicitly, see 15989272ca1SMauro Carvalho Chehab the above extent_cache mount option. 16089272ca1SMauro Carvalho Chehabnoinline_data Disable the inline data feature, inline data feature is 16189272ca1SMauro Carvalho Chehab enabled by default. 16289272ca1SMauro Carvalho Chehabdata_flush Enable data flushing before checkpoint in order to 16389272ca1SMauro Carvalho Chehab persist data of regular and symlink. 16489272ca1SMauro Carvalho Chehabreserve_root=%d Support configuring reserved space which is used for 16589272ca1SMauro Carvalho Chehab allocation from a privileged user with specified uid or 16689272ca1SMauro Carvalho Chehab gid, unit: 4KB, the default limit is 0.2% of user blocks. 16789272ca1SMauro Carvalho Chehabresuid=%d The user ID which may use the reserved blocks. 16889272ca1SMauro Carvalho Chehabresgid=%d The group ID which may use the reserved blocks. 16989272ca1SMauro Carvalho Chehabfault_injection=%d Enable fault injection in all supported types with 17089272ca1SMauro Carvalho Chehab specified injection rate. 17189272ca1SMauro Carvalho Chehabfault_type=%d Support configuring fault injection type, should be 17289272ca1SMauro Carvalho Chehab enabled with fault_injection option, fault type value 17389272ca1SMauro Carvalho Chehab is shown below, it supports single or combined type. 17489272ca1SMauro Carvalho Chehab 17589272ca1SMauro Carvalho Chehab =================== =========== 17689272ca1SMauro Carvalho Chehab Type_Name Type_Value 17789272ca1SMauro Carvalho Chehab =================== =========== 17889272ca1SMauro Carvalho Chehab FAULT_KMALLOC 0x000000001 17989272ca1SMauro Carvalho Chehab FAULT_KVMALLOC 0x000000002 18089272ca1SMauro Carvalho Chehab FAULT_PAGE_ALLOC 0x000000004 18189272ca1SMauro Carvalho Chehab FAULT_PAGE_GET 0x000000008 18289272ca1SMauro Carvalho Chehab FAULT_ALLOC_BIO 0x000000010 18389272ca1SMauro Carvalho Chehab FAULT_ALLOC_NID 0x000000020 18489272ca1SMauro Carvalho Chehab FAULT_ORPHAN 0x000000040 18589272ca1SMauro Carvalho Chehab FAULT_BLOCK 0x000000080 18689272ca1SMauro Carvalho Chehab FAULT_DIR_DEPTH 0x000000100 18789272ca1SMauro Carvalho Chehab FAULT_EVICT_INODE 0x000000200 18889272ca1SMauro Carvalho Chehab FAULT_TRUNCATE 0x000000400 18989272ca1SMauro Carvalho Chehab FAULT_READ_IO 0x000000800 19089272ca1SMauro Carvalho Chehab FAULT_CHECKPOINT 0x000001000 19189272ca1SMauro Carvalho Chehab FAULT_DISCARD 0x000002000 19289272ca1SMauro Carvalho Chehab FAULT_WRITE_IO 0x000004000 19389272ca1SMauro Carvalho Chehab =================== =========== 19489272ca1SMauro Carvalho Chehabmode=%s Control block allocation mode which supports "adaptive" 19589272ca1SMauro Carvalho Chehab and "lfs". In "lfs" mode, there should be no random 19689272ca1SMauro Carvalho Chehab writes towards main area. 19789272ca1SMauro Carvalho Chehabio_bits=%u Set the bit size of write IO requests. It should be set 19889272ca1SMauro Carvalho Chehab with "mode=lfs". 19989272ca1SMauro Carvalho Chehabusrquota Enable plain user disk quota accounting. 20089272ca1SMauro Carvalho Chehabgrpquota Enable plain group disk quota accounting. 20189272ca1SMauro Carvalho Chehabprjquota Enable plain project quota accounting. 20289272ca1SMauro Carvalho Chehabusrjquota=<file> Appoint specified file and type during mount, so that quota 20389272ca1SMauro Carvalho Chehabgrpjquota=<file> information can be properly updated during recovery flow, 20489272ca1SMauro Carvalho Chehabprjjquota=<file> <quota file>: must be in root directory; 20589272ca1SMauro Carvalho Chehabjqfmt=<quota type> <quota type>: [vfsold,vfsv0,vfsv1]. 20689272ca1SMauro Carvalho Chehaboffusrjquota Turn off user journelled quota. 20789272ca1SMauro Carvalho Chehaboffgrpjquota Turn off group journelled quota. 20889272ca1SMauro Carvalho Chehaboffprjjquota Turn off project journelled quota. 20989272ca1SMauro Carvalho Chehabquota Enable plain user disk quota accounting. 21089272ca1SMauro Carvalho Chehabnoquota Disable all plain disk quota option. 21189272ca1SMauro Carvalho Chehabwhint_mode=%s Control which write hints are passed down to block 21289272ca1SMauro Carvalho Chehab layer. This supports "off", "user-based", and 21389272ca1SMauro Carvalho Chehab "fs-based". In "off" mode (default), f2fs does not pass 21489272ca1SMauro Carvalho Chehab down hints. In "user-based" mode, f2fs tries to pass 21589272ca1SMauro Carvalho Chehab down hints given by users. And in "fs-based" mode, f2fs 21689272ca1SMauro Carvalho Chehab passes down hints with its policy. 21789272ca1SMauro Carvalho Chehaballoc_mode=%s Adjust block allocation policy, which supports "reuse" 21889272ca1SMauro Carvalho Chehab and "default". 21989272ca1SMauro Carvalho Chehabfsync_mode=%s Control the policy of fsync. Currently supports "posix", 22089272ca1SMauro Carvalho Chehab "strict", and "nobarrier". In "posix" mode, which is 22189272ca1SMauro Carvalho Chehab default, fsync will follow POSIX semantics and does a 22289272ca1SMauro Carvalho Chehab light operation to improve the filesystem performance. 22389272ca1SMauro Carvalho Chehab In "strict" mode, fsync will be heavy and behaves in line 22489272ca1SMauro Carvalho Chehab with xfs, ext4 and btrfs, where xfstest generic/342 will 22589272ca1SMauro Carvalho Chehab pass, but the performance will regress. "nobarrier" is 22689272ca1SMauro Carvalho Chehab based on "posix", but doesn't issue flush command for 22789272ca1SMauro Carvalho Chehab non-atomic files likewise "nobarrier" mount option. 228ed318a6cSEric Biggerstest_dummy_encryption 229ed318a6cSEric Biggerstest_dummy_encryption=%s 230ed318a6cSEric Biggers Enable dummy encryption, which provides a fake fscrypt 23189272ca1SMauro Carvalho Chehab context. The fake fscrypt context is used by xfstests. 232ed318a6cSEric Biggers The argument may be either "v1" or "v2", in order to 233ed318a6cSEric Biggers select the corresponding fscrypt policy version. 23489272ca1SMauro Carvalho Chehabcheckpoint=%s[:%u[%]] Set to "disable" to turn off checkpointing. Set to "enable" 23589272ca1SMauro Carvalho Chehab to reenable checkpointing. Is enabled by default. While 23689272ca1SMauro Carvalho Chehab disabled, any unmounting or unexpected shutdowns will cause 23789272ca1SMauro Carvalho Chehab the filesystem contents to appear as they did when the 23889272ca1SMauro Carvalho Chehab filesystem was mounted with that option. 23989272ca1SMauro Carvalho Chehab While mounting with checkpoint=disabled, the filesystem must 24089272ca1SMauro Carvalho Chehab run garbage collection to ensure that all available space can 24189272ca1SMauro Carvalho Chehab be used. If this takes too much time, the mount may return 24289272ca1SMauro Carvalho Chehab EAGAIN. You may optionally add a value to indicate how much 24389272ca1SMauro Carvalho Chehab of the disk you would be willing to temporarily give up to 24489272ca1SMauro Carvalho Chehab avoid additional garbage collection. This can be given as a 24589272ca1SMauro Carvalho Chehab number of blocks, or as a percent. For instance, mounting 24689272ca1SMauro Carvalho Chehab with checkpoint=disable:100% would always succeed, but it may 24789272ca1SMauro Carvalho Chehab hide up to all remaining free space. The actual space that 24889272ca1SMauro Carvalho Chehab would be unusable can be viewed at /sys/fs/f2fs/<disk>/unusable 24989272ca1SMauro Carvalho Chehab This space is reclaimed once checkpoint=enable. 250f40f31caSLinus Torvaldscompress_algorithm=%s Control compress algorithm, currently f2fs supports "lzo", 2516d92b201SChao Yu "lz4", "zstd" and "lzo-rle" algorithm. 25289272ca1SMauro Carvalho Chehabcompress_log_size=%u Support configuring compress cluster size, the size will 25389272ca1SMauro Carvalho Chehab be 4KB * (1 << %u), 16KB is minimum size, also it's 25489272ca1SMauro Carvalho Chehab default size. 25589272ca1SMauro Carvalho Chehabcompress_extension=%s Support adding specified extension, so that f2fs can enable 25689272ca1SMauro Carvalho Chehab compression on those corresponding files, e.g. if all files 25789272ca1SMauro Carvalho Chehab with '.ext' has high compression rate, we can set the '.ext' 25889272ca1SMauro Carvalho Chehab on compression extension list and enable compression on 25989272ca1SMauro Carvalho Chehab these file by default rather than to enable it via ioctl. 26089272ca1SMauro Carvalho Chehab For other files, we can still enable compression via ioctl. 261fa679555SChao Yu Note that, there is one reserved special extension '*', it 262fa679555SChao Yu can be set to enable compression for all files. 2632324d50dSLinus Torvaldsinlinecrypt When possible, encrypt/decrypt the contents of encrypted 26427aacd28SSatya Tangirala files using the blk-crypto framework rather than 26527aacd28SSatya Tangirala filesystem-layer encryption. This allows the use of 26627aacd28SSatya Tangirala inline encryption hardware. The on-disk format is 26727aacd28SSatya Tangirala unaffected. For more details, see 26827aacd28SSatya Tangirala Documentation/block/inline-encryption.rst. 2699aa1ccb4SJonathan Corbet======================== ============================================================ 27089272ca1SMauro Carvalho Chehab 27189272ca1SMauro Carvalho ChehabDebugfs Entries 27289272ca1SMauro Carvalho Chehab=============== 27389272ca1SMauro Carvalho Chehab 27489272ca1SMauro Carvalho Chehab/sys/kernel/debug/f2fs/ contains information about all the partitions mounted as 27589272ca1SMauro Carvalho Chehabf2fs. Each file shows the whole f2fs information. 27689272ca1SMauro Carvalho Chehab 27789272ca1SMauro Carvalho Chehab/sys/kernel/debug/f2fs/status includes: 27889272ca1SMauro Carvalho Chehab 27989272ca1SMauro Carvalho Chehab - major file system information managed by f2fs currently 28089272ca1SMauro Carvalho Chehab - average SIT information about whole segments 28189272ca1SMauro Carvalho Chehab - current memory footprint consumed by f2fs. 28289272ca1SMauro Carvalho Chehab 28389272ca1SMauro Carvalho ChehabSysfs Entries 28489272ca1SMauro Carvalho Chehab============= 28589272ca1SMauro Carvalho Chehab 28689272ca1SMauro Carvalho ChehabInformation about mounted f2fs file systems can be found in 28789272ca1SMauro Carvalho Chehab/sys/fs/f2fs. Each mounted filesystem will have a directory in 28889272ca1SMauro Carvalho Chehab/sys/fs/f2fs based on its device name (i.e., /sys/fs/f2fs/sda). 28989272ca1SMauro Carvalho ChehabThe files in each per-device directory are shown in table below. 29089272ca1SMauro Carvalho Chehab 29189272ca1SMauro Carvalho ChehabFiles in /sys/fs/f2fs/<devname> 29289272ca1SMauro Carvalho Chehab(see also Documentation/ABI/testing/sysfs-fs-f2fs) 29389272ca1SMauro Carvalho Chehab 29489272ca1SMauro Carvalho ChehabUsage 29589272ca1SMauro Carvalho Chehab===== 29689272ca1SMauro Carvalho Chehab 29789272ca1SMauro Carvalho Chehab1. Download userland tools and compile them. 29889272ca1SMauro Carvalho Chehab 29989272ca1SMauro Carvalho Chehab2. Skip, if f2fs was compiled statically inside kernel. 30089272ca1SMauro Carvalho Chehab Otherwise, insert the f2fs.ko module:: 30189272ca1SMauro Carvalho Chehab 30289272ca1SMauro Carvalho Chehab # insmod f2fs.ko 30389272ca1SMauro Carvalho Chehab 30489272ca1SMauro Carvalho Chehab3. Create a directory trying to mount:: 30589272ca1SMauro Carvalho Chehab 30689272ca1SMauro Carvalho Chehab # mkdir /mnt/f2fs 30789272ca1SMauro Carvalho Chehab 30889272ca1SMauro Carvalho Chehab4. Format the block device, and then mount as f2fs:: 30989272ca1SMauro Carvalho Chehab 31089272ca1SMauro Carvalho Chehab # mkfs.f2fs -l label /dev/block_device 31189272ca1SMauro Carvalho Chehab # mount -t f2fs /dev/block_device /mnt/f2fs 31289272ca1SMauro Carvalho Chehab 31389272ca1SMauro Carvalho Chehabmkfs.f2fs 31489272ca1SMauro Carvalho Chehab--------- 31589272ca1SMauro Carvalho ChehabThe mkfs.f2fs is for the use of formatting a partition as the f2fs filesystem, 31689272ca1SMauro Carvalho Chehabwhich builds a basic on-disk layout. 31789272ca1SMauro Carvalho Chehab 31889272ca1SMauro Carvalho ChehabThe options consist of: 31989272ca1SMauro Carvalho Chehab 32089272ca1SMauro Carvalho Chehab=============== =========================================================== 32189272ca1SMauro Carvalho Chehab``-l [label]`` Give a volume label, up to 512 unicode name. 32289272ca1SMauro Carvalho Chehab``-a [0 or 1]`` Split start location of each area for heap-based allocation. 32389272ca1SMauro Carvalho Chehab 32489272ca1SMauro Carvalho Chehab 1 is set by default, which performs this. 32589272ca1SMauro Carvalho Chehab``-o [int]`` Set overprovision ratio in percent over volume size. 32689272ca1SMauro Carvalho Chehab 32789272ca1SMauro Carvalho Chehab 5 is set by default. 32889272ca1SMauro Carvalho Chehab``-s [int]`` Set the number of segments per section. 32989272ca1SMauro Carvalho Chehab 33089272ca1SMauro Carvalho Chehab 1 is set by default. 33189272ca1SMauro Carvalho Chehab``-z [int]`` Set the number of sections per zone. 33289272ca1SMauro Carvalho Chehab 33389272ca1SMauro Carvalho Chehab 1 is set by default. 33489272ca1SMauro Carvalho Chehab``-e [str]`` Set basic extension list. e.g. "mp3,gif,mov" 33589272ca1SMauro Carvalho Chehab``-t [0 or 1]`` Disable discard command or not. 33689272ca1SMauro Carvalho Chehab 33789272ca1SMauro Carvalho Chehab 1 is set by default, which conducts discard. 33889272ca1SMauro Carvalho Chehab=============== =========================================================== 33989272ca1SMauro Carvalho Chehab 34089272ca1SMauro Carvalho Chehabfsck.f2fs 34189272ca1SMauro Carvalho Chehab--------- 34289272ca1SMauro Carvalho ChehabThe fsck.f2fs is a tool to check the consistency of an f2fs-formatted 34389272ca1SMauro Carvalho Chehabpartition, which examines whether the filesystem metadata and user-made data 34489272ca1SMauro Carvalho Chehabare cross-referenced correctly or not. 34589272ca1SMauro Carvalho ChehabNote that, initial version of the tool does not fix any inconsistency. 34689272ca1SMauro Carvalho Chehab 34789272ca1SMauro Carvalho ChehabThe options consist of:: 34889272ca1SMauro Carvalho Chehab 34989272ca1SMauro Carvalho Chehab -d debug level [default:0] 35089272ca1SMauro Carvalho Chehab 35189272ca1SMauro Carvalho Chehabdump.f2fs 35289272ca1SMauro Carvalho Chehab--------- 35389272ca1SMauro Carvalho ChehabThe dump.f2fs shows the information of specific inode and dumps SSA and SIT to 35489272ca1SMauro Carvalho Chehabfile. Each file is dump_ssa and dump_sit. 35589272ca1SMauro Carvalho Chehab 35689272ca1SMauro Carvalho ChehabThe dump.f2fs is used to debug on-disk data structures of the f2fs filesystem. 35789272ca1SMauro Carvalho ChehabIt shows on-disk inode information recognized by a given inode number, and is 35889272ca1SMauro Carvalho Chehabable to dump all the SSA and SIT entries into predefined files, ./dump_ssa and 35989272ca1SMauro Carvalho Chehab./dump_sit respectively. 36089272ca1SMauro Carvalho Chehab 36189272ca1SMauro Carvalho ChehabThe options consist of:: 36289272ca1SMauro Carvalho Chehab 36389272ca1SMauro Carvalho Chehab -d debug level [default:0] 36489272ca1SMauro Carvalho Chehab -i inode no (hex) 36589272ca1SMauro Carvalho Chehab -s [SIT dump segno from #1~#2 (decimal), for all 0~-1] 36689272ca1SMauro Carvalho Chehab -a [SSA dump segno from #1~#2 (decimal), for all 0~-1] 36789272ca1SMauro Carvalho Chehab 36889272ca1SMauro Carvalho ChehabExamples:: 36989272ca1SMauro Carvalho Chehab 37089272ca1SMauro Carvalho Chehab # dump.f2fs -i [ino] /dev/sdx 37189272ca1SMauro Carvalho Chehab # dump.f2fs -s 0~-1 /dev/sdx (SIT dump) 37289272ca1SMauro Carvalho Chehab # dump.f2fs -a 0~-1 /dev/sdx (SSA dump) 37389272ca1SMauro Carvalho Chehab 37489272ca1SMauro Carvalho ChehabDesign 37589272ca1SMauro Carvalho Chehab====== 37689272ca1SMauro Carvalho Chehab 37789272ca1SMauro Carvalho ChehabOn-disk Layout 37889272ca1SMauro Carvalho Chehab-------------- 37989272ca1SMauro Carvalho Chehab 38089272ca1SMauro Carvalho ChehabF2FS divides the whole volume into a number of segments, each of which is fixed 38189272ca1SMauro Carvalho Chehabto 2MB in size. A section is composed of consecutive segments, and a zone 38289272ca1SMauro Carvalho Chehabconsists of a set of sections. By default, section and zone sizes are set to one 38389272ca1SMauro Carvalho Chehabsegment size identically, but users can easily modify the sizes by mkfs. 38489272ca1SMauro Carvalho Chehab 38589272ca1SMauro Carvalho ChehabF2FS splits the entire volume into six areas, and all the areas except superblock 38689272ca1SMauro Carvalho Chehabconsists of multiple segments as described below:: 38789272ca1SMauro Carvalho Chehab 38889272ca1SMauro Carvalho Chehab align with the zone size <-| 38989272ca1SMauro Carvalho Chehab |-> align with the segment size 39089272ca1SMauro Carvalho Chehab _________________________________________________________________________ 39189272ca1SMauro Carvalho Chehab | | | Segment | Node | Segment | | 39289272ca1SMauro Carvalho Chehab | Superblock | Checkpoint | Info. | Address | Summary | Main | 39389272ca1SMauro Carvalho Chehab | (SB) | (CP) | Table (SIT) | Table (NAT) | Area (SSA) | | 39489272ca1SMauro Carvalho Chehab |____________|_____2______|______N______|______N______|______N_____|__N___| 39589272ca1SMauro Carvalho Chehab . . 39689272ca1SMauro Carvalho Chehab . . 39789272ca1SMauro Carvalho Chehab . . 39889272ca1SMauro Carvalho Chehab ._________________________________________. 39989272ca1SMauro Carvalho Chehab |_Segment_|_..._|_Segment_|_..._|_Segment_| 40089272ca1SMauro Carvalho Chehab . . 40189272ca1SMauro Carvalho Chehab ._________._________ 40289272ca1SMauro Carvalho Chehab |_section_|__...__|_ 40389272ca1SMauro Carvalho Chehab . . 40489272ca1SMauro Carvalho Chehab .________. 40589272ca1SMauro Carvalho Chehab |__zone__| 40689272ca1SMauro Carvalho Chehab 40789272ca1SMauro Carvalho Chehab- Superblock (SB) 40889272ca1SMauro Carvalho Chehab It is located at the beginning of the partition, and there exist two copies 40989272ca1SMauro Carvalho Chehab to avoid file system crash. It contains basic partition information and some 41089272ca1SMauro Carvalho Chehab default parameters of f2fs. 41189272ca1SMauro Carvalho Chehab 41289272ca1SMauro Carvalho Chehab- Checkpoint (CP) 41389272ca1SMauro Carvalho Chehab It contains file system information, bitmaps for valid NAT/SIT sets, orphan 41489272ca1SMauro Carvalho Chehab inode lists, and summary entries of current active segments. 41589272ca1SMauro Carvalho Chehab 41689272ca1SMauro Carvalho Chehab- Segment Information Table (SIT) 41789272ca1SMauro Carvalho Chehab It contains segment information such as valid block count and bitmap for the 41889272ca1SMauro Carvalho Chehab validity of all the blocks. 41989272ca1SMauro Carvalho Chehab 42089272ca1SMauro Carvalho Chehab- Node Address Table (NAT) 42189272ca1SMauro Carvalho Chehab It is composed of a block address table for all the node blocks stored in 42289272ca1SMauro Carvalho Chehab Main area. 42389272ca1SMauro Carvalho Chehab 42489272ca1SMauro Carvalho Chehab- Segment Summary Area (SSA) 42589272ca1SMauro Carvalho Chehab It contains summary entries which contains the owner information of all the 42689272ca1SMauro Carvalho Chehab data and node blocks stored in Main area. 42789272ca1SMauro Carvalho Chehab 42889272ca1SMauro Carvalho Chehab- Main Area 42989272ca1SMauro Carvalho Chehab It contains file and directory data including their indices. 43089272ca1SMauro Carvalho Chehab 43189272ca1SMauro Carvalho ChehabIn order to avoid misalignment between file system and flash-based storage, F2FS 43289272ca1SMauro Carvalho Chehabaligns the start block address of CP with the segment size. Also, it aligns the 43389272ca1SMauro Carvalho Chehabstart block address of Main area with the zone size by reserving some segments 43489272ca1SMauro Carvalho Chehabin SSA area. 43589272ca1SMauro Carvalho Chehab 43689272ca1SMauro Carvalho ChehabReference the following survey for additional technical details. 43789272ca1SMauro Carvalho Chehabhttps://wiki.linaro.org/WorkingGroups/Kernel/Projects/FlashCardSurvey 43889272ca1SMauro Carvalho Chehab 43989272ca1SMauro Carvalho ChehabFile System Metadata Structure 44089272ca1SMauro Carvalho Chehab------------------------------ 44189272ca1SMauro Carvalho Chehab 44289272ca1SMauro Carvalho ChehabF2FS adopts the checkpointing scheme to maintain file system consistency. At 44389272ca1SMauro Carvalho Chehabmount time, F2FS first tries to find the last valid checkpoint data by scanning 44489272ca1SMauro Carvalho ChehabCP area. In order to reduce the scanning time, F2FS uses only two copies of CP. 44589272ca1SMauro Carvalho ChehabOne of them always indicates the last valid data, which is called as shadow copy 44689272ca1SMauro Carvalho Chehabmechanism. In addition to CP, NAT and SIT also adopt the shadow copy mechanism. 44789272ca1SMauro Carvalho Chehab 44889272ca1SMauro Carvalho ChehabFor file system consistency, each CP points to which NAT and SIT copies are 44989272ca1SMauro Carvalho Chehabvalid, as shown as below:: 45089272ca1SMauro Carvalho Chehab 45189272ca1SMauro Carvalho Chehab +--------+----------+---------+ 45289272ca1SMauro Carvalho Chehab | CP | SIT | NAT | 45389272ca1SMauro Carvalho Chehab +--------+----------+---------+ 45489272ca1SMauro Carvalho Chehab . . . . 45589272ca1SMauro Carvalho Chehab . . . . 45689272ca1SMauro Carvalho Chehab . . . . 45789272ca1SMauro Carvalho Chehab +-------+-------+--------+--------+--------+--------+ 45889272ca1SMauro Carvalho Chehab | CP #0 | CP #1 | SIT #0 | SIT #1 | NAT #0 | NAT #1 | 45989272ca1SMauro Carvalho Chehab +-------+-------+--------+--------+--------+--------+ 46089272ca1SMauro Carvalho Chehab | ^ ^ 46189272ca1SMauro Carvalho Chehab | | | 46289272ca1SMauro Carvalho Chehab `----------------------------------------' 46389272ca1SMauro Carvalho Chehab 46489272ca1SMauro Carvalho ChehabIndex Structure 46589272ca1SMauro Carvalho Chehab--------------- 46689272ca1SMauro Carvalho Chehab 46789272ca1SMauro Carvalho ChehabThe key data structure to manage the data locations is a "node". Similar to 46889272ca1SMauro Carvalho Chehabtraditional file structures, F2FS has three types of node: inode, direct node, 46989272ca1SMauro Carvalho Chehabindirect node. F2FS assigns 4KB to an inode block which contains 923 data block 47089272ca1SMauro Carvalho Chehabindices, two direct node pointers, two indirect node pointers, and one double 47189272ca1SMauro Carvalho Chehabindirect node pointer as described below. One direct node block contains 1018 47289272ca1SMauro Carvalho Chehabdata blocks, and one indirect node block contains also 1018 node blocks. Thus, 47389272ca1SMauro Carvalho Chehabone inode block (i.e., a file) covers:: 47489272ca1SMauro Carvalho Chehab 47589272ca1SMauro Carvalho Chehab 4KB * (923 + 2 * 1018 + 2 * 1018 * 1018 + 1018 * 1018 * 1018) := 3.94TB. 47689272ca1SMauro Carvalho Chehab 47789272ca1SMauro Carvalho Chehab Inode block (4KB) 47889272ca1SMauro Carvalho Chehab |- data (923) 47989272ca1SMauro Carvalho Chehab |- direct node (2) 48089272ca1SMauro Carvalho Chehab | `- data (1018) 48189272ca1SMauro Carvalho Chehab |- indirect node (2) 48289272ca1SMauro Carvalho Chehab | `- direct node (1018) 48389272ca1SMauro Carvalho Chehab | `- data (1018) 48489272ca1SMauro Carvalho Chehab `- double indirect node (1) 48589272ca1SMauro Carvalho Chehab `- indirect node (1018) 48689272ca1SMauro Carvalho Chehab `- direct node (1018) 48789272ca1SMauro Carvalho Chehab `- data (1018) 48889272ca1SMauro Carvalho Chehab 48989272ca1SMauro Carvalho ChehabNote that, all the node blocks are mapped by NAT which means the location of 49089272ca1SMauro Carvalho Chehabeach node is translated by the NAT table. In the consideration of the wandering 49189272ca1SMauro Carvalho Chehabtree problem, F2FS is able to cut off the propagation of node updates caused by 49289272ca1SMauro Carvalho Chehableaf data writes. 49389272ca1SMauro Carvalho Chehab 49489272ca1SMauro Carvalho ChehabDirectory Structure 49589272ca1SMauro Carvalho Chehab------------------- 49689272ca1SMauro Carvalho Chehab 49789272ca1SMauro Carvalho ChehabA directory entry occupies 11 bytes, which consists of the following attributes. 49889272ca1SMauro Carvalho Chehab 49989272ca1SMauro Carvalho Chehab- hash hash value of the file name 50089272ca1SMauro Carvalho Chehab- ino inode number 50189272ca1SMauro Carvalho Chehab- len the length of file name 50289272ca1SMauro Carvalho Chehab- type file type such as directory, symlink, etc 50389272ca1SMauro Carvalho Chehab 50489272ca1SMauro Carvalho ChehabA dentry block consists of 214 dentry slots and file names. Therein a bitmap is 50589272ca1SMauro Carvalho Chehabused to represent whether each dentry is valid or not. A dentry block occupies 50689272ca1SMauro Carvalho Chehab4KB with the following composition. 50789272ca1SMauro Carvalho Chehab 50889272ca1SMauro Carvalho Chehab:: 50989272ca1SMauro Carvalho Chehab 51089272ca1SMauro Carvalho Chehab Dentry Block(4 K) = bitmap (27 bytes) + reserved (3 bytes) + 51189272ca1SMauro Carvalho Chehab dentries(11 * 214 bytes) + file name (8 * 214 bytes) 51289272ca1SMauro Carvalho Chehab 51389272ca1SMauro Carvalho Chehab [Bucket] 51489272ca1SMauro Carvalho Chehab +--------------------------------+ 51589272ca1SMauro Carvalho Chehab |dentry block 1 | dentry block 2 | 51689272ca1SMauro Carvalho Chehab +--------------------------------+ 51789272ca1SMauro Carvalho Chehab . . 51889272ca1SMauro Carvalho Chehab . . 51989272ca1SMauro Carvalho Chehab . [Dentry Block Structure: 4KB] . 52089272ca1SMauro Carvalho Chehab +--------+----------+----------+------------+ 52189272ca1SMauro Carvalho Chehab | bitmap | reserved | dentries | file names | 52289272ca1SMauro Carvalho Chehab +--------+----------+----------+------------+ 52389272ca1SMauro Carvalho Chehab [Dentry Block: 4KB] . . 52489272ca1SMauro Carvalho Chehab . . 52589272ca1SMauro Carvalho Chehab . . 52689272ca1SMauro Carvalho Chehab +------+------+-----+------+ 52789272ca1SMauro Carvalho Chehab | hash | ino | len | type | 52889272ca1SMauro Carvalho Chehab +------+------+-----+------+ 52989272ca1SMauro Carvalho Chehab [Dentry Structure: 11 bytes] 53089272ca1SMauro Carvalho Chehab 53189272ca1SMauro Carvalho ChehabF2FS implements multi-level hash tables for directory structure. Each level has 53289272ca1SMauro Carvalho Chehaba hash table with dedicated number of hash buckets as shown below. Note that 53389272ca1SMauro Carvalho Chehab"A(2B)" means a bucket includes 2 data blocks. 53489272ca1SMauro Carvalho Chehab 53589272ca1SMauro Carvalho Chehab:: 53689272ca1SMauro Carvalho Chehab 53789272ca1SMauro Carvalho Chehab ---------------------- 53889272ca1SMauro Carvalho Chehab A : bucket 53989272ca1SMauro Carvalho Chehab B : block 54089272ca1SMauro Carvalho Chehab N : MAX_DIR_HASH_DEPTH 54189272ca1SMauro Carvalho Chehab ---------------------- 54289272ca1SMauro Carvalho Chehab 54389272ca1SMauro Carvalho Chehab level #0 | A(2B) 54489272ca1SMauro Carvalho Chehab | 54589272ca1SMauro Carvalho Chehab level #1 | A(2B) - A(2B) 54689272ca1SMauro Carvalho Chehab | 54789272ca1SMauro Carvalho Chehab level #2 | A(2B) - A(2B) - A(2B) - A(2B) 54889272ca1SMauro Carvalho Chehab . | . . . . 54989272ca1SMauro Carvalho Chehab level #N/2 | A(2B) - A(2B) - A(2B) - A(2B) - A(2B) - ... - A(2B) 55089272ca1SMauro Carvalho Chehab . | . . . . 55189272ca1SMauro Carvalho Chehab level #N | A(4B) - A(4B) - A(4B) - A(4B) - A(4B) - ... - A(4B) 55289272ca1SMauro Carvalho Chehab 55389272ca1SMauro Carvalho ChehabThe number of blocks and buckets are determined by:: 55489272ca1SMauro Carvalho Chehab 55589272ca1SMauro Carvalho Chehab ,- 2, if n < MAX_DIR_HASH_DEPTH / 2, 55689272ca1SMauro Carvalho Chehab # of blocks in level #n = | 55789272ca1SMauro Carvalho Chehab `- 4, Otherwise 55889272ca1SMauro Carvalho Chehab 55989272ca1SMauro Carvalho Chehab ,- 2^(n + dir_level), 56089272ca1SMauro Carvalho Chehab | if n + dir_level < MAX_DIR_HASH_DEPTH / 2, 56189272ca1SMauro Carvalho Chehab # of buckets in level #n = | 56289272ca1SMauro Carvalho Chehab `- 2^((MAX_DIR_HASH_DEPTH / 2) - 1), 56389272ca1SMauro Carvalho Chehab Otherwise 56489272ca1SMauro Carvalho Chehab 56589272ca1SMauro Carvalho ChehabWhen F2FS finds a file name in a directory, at first a hash value of the file 56689272ca1SMauro Carvalho Chehabname is calculated. Then, F2FS scans the hash table in level #0 to find the 56789272ca1SMauro Carvalho Chehabdentry consisting of the file name and its inode number. If not found, F2FS 56889272ca1SMauro Carvalho Chehabscans the next hash table in level #1. In this way, F2FS scans hash tables in 56989272ca1SMauro Carvalho Chehabeach levels incrementally from 1 to N. In each levels F2FS needs to scan only 57089272ca1SMauro Carvalho Chehabone bucket determined by the following equation, which shows O(log(# of files)) 57189272ca1SMauro Carvalho Chehabcomplexity:: 57289272ca1SMauro Carvalho Chehab 57389272ca1SMauro Carvalho Chehab bucket number to scan in level #n = (hash value) % (# of buckets in level #n) 57489272ca1SMauro Carvalho Chehab 57589272ca1SMauro Carvalho ChehabIn the case of file creation, F2FS finds empty consecutive slots that cover the 57689272ca1SMauro Carvalho Chehabfile name. F2FS searches the empty slots in the hash tables of whole levels from 57789272ca1SMauro Carvalho Chehab1 to N in the same way as the lookup operation. 57889272ca1SMauro Carvalho Chehab 57989272ca1SMauro Carvalho ChehabThe following figure shows an example of two cases holding children:: 58089272ca1SMauro Carvalho Chehab 58189272ca1SMauro Carvalho Chehab --------------> Dir <-------------- 58289272ca1SMauro Carvalho Chehab | | 58389272ca1SMauro Carvalho Chehab child child 58489272ca1SMauro Carvalho Chehab 58589272ca1SMauro Carvalho Chehab child - child [hole] - child 58689272ca1SMauro Carvalho Chehab 58789272ca1SMauro Carvalho Chehab child - child - child [hole] - [hole] - child 58889272ca1SMauro Carvalho Chehab 58989272ca1SMauro Carvalho Chehab Case 1: Case 2: 59089272ca1SMauro Carvalho Chehab Number of children = 6, Number of children = 3, 59189272ca1SMauro Carvalho Chehab File size = 7 File size = 7 59289272ca1SMauro Carvalho Chehab 59389272ca1SMauro Carvalho ChehabDefault Block Allocation 59489272ca1SMauro Carvalho Chehab------------------------ 59589272ca1SMauro Carvalho Chehab 59689272ca1SMauro Carvalho ChehabAt runtime, F2FS manages six active logs inside "Main" area: Hot/Warm/Cold node 59789272ca1SMauro Carvalho Chehaband Hot/Warm/Cold data. 59889272ca1SMauro Carvalho Chehab 59989272ca1SMauro Carvalho Chehab- Hot node contains direct node blocks of directories. 60089272ca1SMauro Carvalho Chehab- Warm node contains direct node blocks except hot node blocks. 60189272ca1SMauro Carvalho Chehab- Cold node contains indirect node blocks 60289272ca1SMauro Carvalho Chehab- Hot data contains dentry blocks 60389272ca1SMauro Carvalho Chehab- Warm data contains data blocks except hot and cold data blocks 60489272ca1SMauro Carvalho Chehab- Cold data contains multimedia data or migrated data blocks 60589272ca1SMauro Carvalho Chehab 60689272ca1SMauro Carvalho ChehabLFS has two schemes for free space management: threaded log and copy-and-compac- 60789272ca1SMauro Carvalho Chehabtion. The copy-and-compaction scheme which is known as cleaning, is well-suited 60889272ca1SMauro Carvalho Chehabfor devices showing very good sequential write performance, since free segments 60989272ca1SMauro Carvalho Chehabare served all the time for writing new data. However, it suffers from cleaning 61089272ca1SMauro Carvalho Chehaboverhead under high utilization. Contrarily, the threaded log scheme suffers 61189272ca1SMauro Carvalho Chehabfrom random writes, but no cleaning process is needed. F2FS adopts a hybrid 61289272ca1SMauro Carvalho Chehabscheme where the copy-and-compaction scheme is adopted by default, but the 61389272ca1SMauro Carvalho Chehabpolicy is dynamically changed to the threaded log scheme according to the file 61489272ca1SMauro Carvalho Chehabsystem status. 61589272ca1SMauro Carvalho Chehab 61689272ca1SMauro Carvalho ChehabIn order to align F2FS with underlying flash-based storage, F2FS allocates a 61789272ca1SMauro Carvalho Chehabsegment in a unit of section. F2FS expects that the section size would be the 61889272ca1SMauro Carvalho Chehabsame as the unit size of garbage collection in FTL. Furthermore, with respect 61989272ca1SMauro Carvalho Chehabto the mapping granularity in FTL, F2FS allocates each section of the active 62089272ca1SMauro Carvalho Chehablogs from different zones as much as possible, since FTL can write the data in 62189272ca1SMauro Carvalho Chehabthe active logs into one allocation unit according to its mapping granularity. 62289272ca1SMauro Carvalho Chehab 62389272ca1SMauro Carvalho ChehabCleaning process 62489272ca1SMauro Carvalho Chehab---------------- 62589272ca1SMauro Carvalho Chehab 62689272ca1SMauro Carvalho ChehabF2FS does cleaning both on demand and in the background. On-demand cleaning is 62789272ca1SMauro Carvalho Chehabtriggered when there are not enough free segments to serve VFS calls. Background 62889272ca1SMauro Carvalho Chehabcleaner is operated by a kernel thread, and triggers the cleaning job when the 62989272ca1SMauro Carvalho Chehabsystem is idle. 63089272ca1SMauro Carvalho Chehab 63189272ca1SMauro Carvalho ChehabF2FS supports two victim selection policies: greedy and cost-benefit algorithms. 63289272ca1SMauro Carvalho ChehabIn the greedy algorithm, F2FS selects a victim segment having the smallest number 63389272ca1SMauro Carvalho Chehabof valid blocks. In the cost-benefit algorithm, F2FS selects a victim segment 63489272ca1SMauro Carvalho Chehabaccording to the segment age and the number of valid blocks in order to address 63589272ca1SMauro Carvalho Chehablog block thrashing problem in the greedy algorithm. F2FS adopts the greedy 63689272ca1SMauro Carvalho Chehabalgorithm for on-demand cleaner, while background cleaner adopts cost-benefit 63789272ca1SMauro Carvalho Chehabalgorithm. 63889272ca1SMauro Carvalho Chehab 63989272ca1SMauro Carvalho ChehabIn order to identify whether the data in the victim segment are valid or not, 64089272ca1SMauro Carvalho ChehabF2FS manages a bitmap. Each bit represents the validity of a block, and the 64189272ca1SMauro Carvalho Chehabbitmap is composed of a bit stream covering whole blocks in main area. 64289272ca1SMauro Carvalho Chehab 64389272ca1SMauro Carvalho ChehabWrite-hint Policy 64489272ca1SMauro Carvalho Chehab----------------- 64589272ca1SMauro Carvalho Chehab 64689272ca1SMauro Carvalho Chehab1) whint_mode=off. F2FS only passes down WRITE_LIFE_NOT_SET. 64789272ca1SMauro Carvalho Chehab 64889272ca1SMauro Carvalho Chehab2) whint_mode=user-based. F2FS tries to pass down hints given by 64989272ca1SMauro Carvalho Chehabusers. 65089272ca1SMauro Carvalho Chehab 65189272ca1SMauro Carvalho Chehab===================== ======================== =================== 65289272ca1SMauro Carvalho ChehabUser F2FS Block 65389272ca1SMauro Carvalho Chehab===================== ======================== =================== 65489272ca1SMauro Carvalho Chehab META WRITE_LIFE_NOT_SET 65589272ca1SMauro Carvalho Chehab HOT_NODE " 65689272ca1SMauro Carvalho Chehab WARM_NODE " 65789272ca1SMauro Carvalho Chehab COLD_NODE " 65889272ca1SMauro Carvalho Chehabioctl(COLD) COLD_DATA WRITE_LIFE_EXTREME 65989272ca1SMauro Carvalho Chehabextension list " " 66089272ca1SMauro Carvalho Chehab 66189272ca1SMauro Carvalho Chehab-- buffered io 66289272ca1SMauro Carvalho ChehabWRITE_LIFE_EXTREME COLD_DATA WRITE_LIFE_EXTREME 66389272ca1SMauro Carvalho ChehabWRITE_LIFE_SHORT HOT_DATA WRITE_LIFE_SHORT 66489272ca1SMauro Carvalho ChehabWRITE_LIFE_NOT_SET WARM_DATA WRITE_LIFE_NOT_SET 66589272ca1SMauro Carvalho ChehabWRITE_LIFE_NONE " " 66689272ca1SMauro Carvalho ChehabWRITE_LIFE_MEDIUM " " 66789272ca1SMauro Carvalho ChehabWRITE_LIFE_LONG " " 66889272ca1SMauro Carvalho Chehab 66989272ca1SMauro Carvalho Chehab-- direct io 67089272ca1SMauro Carvalho ChehabWRITE_LIFE_EXTREME COLD_DATA WRITE_LIFE_EXTREME 67189272ca1SMauro Carvalho ChehabWRITE_LIFE_SHORT HOT_DATA WRITE_LIFE_SHORT 67289272ca1SMauro Carvalho ChehabWRITE_LIFE_NOT_SET WARM_DATA WRITE_LIFE_NOT_SET 67389272ca1SMauro Carvalho ChehabWRITE_LIFE_NONE " WRITE_LIFE_NONE 67489272ca1SMauro Carvalho ChehabWRITE_LIFE_MEDIUM " WRITE_LIFE_MEDIUM 67589272ca1SMauro Carvalho ChehabWRITE_LIFE_LONG " WRITE_LIFE_LONG 67689272ca1SMauro Carvalho Chehab===================== ======================== =================== 67789272ca1SMauro Carvalho Chehab 67889272ca1SMauro Carvalho Chehab3) whint_mode=fs-based. F2FS passes down hints with its policy. 67989272ca1SMauro Carvalho Chehab 68089272ca1SMauro Carvalho Chehab===================== ======================== =================== 68189272ca1SMauro Carvalho ChehabUser F2FS Block 68289272ca1SMauro Carvalho Chehab===================== ======================== =================== 68389272ca1SMauro Carvalho Chehab META WRITE_LIFE_MEDIUM; 68489272ca1SMauro Carvalho Chehab HOT_NODE WRITE_LIFE_NOT_SET 68589272ca1SMauro Carvalho Chehab WARM_NODE " 68689272ca1SMauro Carvalho Chehab COLD_NODE WRITE_LIFE_NONE 68789272ca1SMauro Carvalho Chehabioctl(COLD) COLD_DATA WRITE_LIFE_EXTREME 68889272ca1SMauro Carvalho Chehabextension list " " 68989272ca1SMauro Carvalho Chehab 69089272ca1SMauro Carvalho Chehab-- buffered io 69189272ca1SMauro Carvalho ChehabWRITE_LIFE_EXTREME COLD_DATA WRITE_LIFE_EXTREME 69289272ca1SMauro Carvalho ChehabWRITE_LIFE_SHORT HOT_DATA WRITE_LIFE_SHORT 69389272ca1SMauro Carvalho ChehabWRITE_LIFE_NOT_SET WARM_DATA WRITE_LIFE_LONG 69489272ca1SMauro Carvalho ChehabWRITE_LIFE_NONE " " 69589272ca1SMauro Carvalho ChehabWRITE_LIFE_MEDIUM " " 69689272ca1SMauro Carvalho ChehabWRITE_LIFE_LONG " " 69789272ca1SMauro Carvalho Chehab 69889272ca1SMauro Carvalho Chehab-- direct io 69989272ca1SMauro Carvalho ChehabWRITE_LIFE_EXTREME COLD_DATA WRITE_LIFE_EXTREME 70089272ca1SMauro Carvalho ChehabWRITE_LIFE_SHORT HOT_DATA WRITE_LIFE_SHORT 70189272ca1SMauro Carvalho ChehabWRITE_LIFE_NOT_SET WARM_DATA WRITE_LIFE_NOT_SET 70289272ca1SMauro Carvalho ChehabWRITE_LIFE_NONE " WRITE_LIFE_NONE 70389272ca1SMauro Carvalho ChehabWRITE_LIFE_MEDIUM " WRITE_LIFE_MEDIUM 70489272ca1SMauro Carvalho ChehabWRITE_LIFE_LONG " WRITE_LIFE_LONG 70589272ca1SMauro Carvalho Chehab===================== ======================== =================== 70689272ca1SMauro Carvalho Chehab 70789272ca1SMauro Carvalho ChehabFallocate(2) Policy 70889272ca1SMauro Carvalho Chehab------------------- 70989272ca1SMauro Carvalho Chehab 71089272ca1SMauro Carvalho ChehabThe default policy follows the below posix rule. 71189272ca1SMauro Carvalho Chehab 71289272ca1SMauro Carvalho ChehabAllocating disk space 71389272ca1SMauro Carvalho Chehab The default operation (i.e., mode is zero) of fallocate() allocates 71489272ca1SMauro Carvalho Chehab the disk space within the range specified by offset and len. The 71589272ca1SMauro Carvalho Chehab file size (as reported by stat(2)) will be changed if offset+len is 71689272ca1SMauro Carvalho Chehab greater than the file size. Any subregion within the range specified 71789272ca1SMauro Carvalho Chehab by offset and len that did not contain data before the call will be 71889272ca1SMauro Carvalho Chehab initialized to zero. This default behavior closely resembles the 71989272ca1SMauro Carvalho Chehab behavior of the posix_fallocate(3) library function, and is intended 72089272ca1SMauro Carvalho Chehab as a method of optimally implementing that function. 72189272ca1SMauro Carvalho Chehab 72289272ca1SMauro Carvalho ChehabHowever, once F2FS receives ioctl(fd, F2FS_IOC_SET_PIN_FILE) in prior to 72389272ca1SMauro Carvalho Chehabfallocate(fd, DEFAULT_MODE), it allocates on-disk blocks addressess having 72489272ca1SMauro Carvalho Chehabzero or random data, which is useful to the below scenario where: 72589272ca1SMauro Carvalho Chehab 72689272ca1SMauro Carvalho Chehab 1. create(fd) 72789272ca1SMauro Carvalho Chehab 2. ioctl(fd, F2FS_IOC_SET_PIN_FILE) 72889272ca1SMauro Carvalho Chehab 3. fallocate(fd, 0, 0, size) 72989272ca1SMauro Carvalho Chehab 4. address = fibmap(fd, offset) 73089272ca1SMauro Carvalho Chehab 5. open(blkdev) 73189272ca1SMauro Carvalho Chehab 6. write(blkdev, address) 73289272ca1SMauro Carvalho Chehab 73389272ca1SMauro Carvalho ChehabCompression implementation 73489272ca1SMauro Carvalho Chehab-------------------------- 73589272ca1SMauro Carvalho Chehab 73689272ca1SMauro Carvalho Chehab- New term named cluster is defined as basic unit of compression, file can 73789272ca1SMauro Carvalho Chehab be divided into multiple clusters logically. One cluster includes 4 << n 73889272ca1SMauro Carvalho Chehab (n >= 0) logical pages, compression size is also cluster size, each of 73989272ca1SMauro Carvalho Chehab cluster can be compressed or not. 74089272ca1SMauro Carvalho Chehab 74189272ca1SMauro Carvalho Chehab- In cluster metadata layout, one special block address is used to indicate 74289272ca1SMauro Carvalho Chehab cluster is compressed one or normal one, for compressed cluster, following 74389272ca1SMauro Carvalho Chehab metadata maps cluster to [1, 4 << n - 1] physical blocks, in where f2fs 74489272ca1SMauro Carvalho Chehab stores data including compress header and compressed data. 74589272ca1SMauro Carvalho Chehab 74689272ca1SMauro Carvalho Chehab- In order to eliminate write amplification during overwrite, F2FS only 74789272ca1SMauro Carvalho Chehab support compression on write-once file, data can be compressed only when 7484fc781a3SChao Yu all logical blocks in cluster contain valid data and compress ratio of 7494fc781a3SChao Yu cluster data is lower than specified threshold. 75089272ca1SMauro Carvalho Chehab 75189272ca1SMauro Carvalho Chehab- To enable compression on regular inode, there are three ways: 75289272ca1SMauro Carvalho Chehab 75389272ca1SMauro Carvalho Chehab * chattr +c file 75489272ca1SMauro Carvalho Chehab * chattr +c dir; touch dir/file 75589272ca1SMauro Carvalho Chehab * mount w/ -o compress_extension=ext; touch file.ext 75689272ca1SMauro Carvalho Chehab 75789272ca1SMauro Carvalho ChehabCompress metadata layout:: 75889272ca1SMauro Carvalho Chehab 75989272ca1SMauro Carvalho Chehab [Dnode Structure] 76089272ca1SMauro Carvalho Chehab +-----------------------------------------------+ 76189272ca1SMauro Carvalho Chehab | cluster 1 | cluster 2 | ......... | cluster N | 76289272ca1SMauro Carvalho Chehab +-----------------------------------------------+ 76389272ca1SMauro Carvalho Chehab . . . . 76489272ca1SMauro Carvalho Chehab . . . . 76589272ca1SMauro Carvalho Chehab . Compressed Cluster . . Normal Cluster . 76689272ca1SMauro Carvalho Chehab +----------+---------+---------+---------+ +---------+---------+---------+---------+ 76789272ca1SMauro Carvalho Chehab |compr flag| block 1 | block 2 | block 3 | | block 1 | block 2 | block 3 | block 4 | 76889272ca1SMauro Carvalho Chehab +----------+---------+---------+---------+ +---------+---------+---------+---------+ 76989272ca1SMauro Carvalho Chehab . . 77089272ca1SMauro Carvalho Chehab . . 77189272ca1SMauro Carvalho Chehab . . 77289272ca1SMauro Carvalho Chehab +-------------+-------------+----------+----------------------------+ 77389272ca1SMauro Carvalho Chehab | data length | data chksum | reserved | compressed data | 77489272ca1SMauro Carvalho Chehab +-------------+-------------+----------+----------------------------+ 775*de881df9SAravind Ramesh 776*de881df9SAravind RameshNVMe Zoned Namespace devices 777*de881df9SAravind Ramesh---------------------------- 778*de881df9SAravind Ramesh 779*de881df9SAravind Ramesh- ZNS defines a per-zone capacity which can be equal or less than the 780*de881df9SAravind Ramesh zone-size. Zone-capacity is the number of usable blocks in the zone. 781*de881df9SAravind Ramesh F2fs checks if zone-capacity is less than zone-size, if it is, then any 782*de881df9SAravind Ramesh segment which starts after the zone-capacity is marked as not-free in 783*de881df9SAravind Ramesh the free segment bitmap at initial mount time. These segments are marked 784*de881df9SAravind Ramesh as permanently used so they are not allocated for writes and 785*de881df9SAravind Ramesh consequently are not needed to be garbage collected. In case the 786*de881df9SAravind Ramesh zone-capacity is not aligned to default segment size(2MB), then a segment 787*de881df9SAravind Ramesh can start before the zone-capacity and span across zone-capacity boundary. 788*de881df9SAravind Ramesh Such spanning segments are also considered as usable segments. All blocks 789*de881df9SAravind Ramesh past the zone-capacity are considered unusable in these segments. 790