WSL2-Linux-Kernel/Documentation/filesystems/f2fs.rst

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.. SPDX-License-Identifier: GPL-2.0
==========================================
WHAT IS Flash-Friendly File System (F2FS)?
==========================================
NAND flash memory-based storage devices, such as SSD, eMMC, and SD cards, have
been equipped on a variety systems ranging from mobile to server systems. Since
they are known to have different characteristics from the conventional rotating
disks, a file system, an upper layer to the storage device, should adapt to the
changes from the sketch in the design level.
F2FS is a file system exploiting NAND flash memory-based storage devices, which
is based on Log-structured File System (LFS). The design has been focused on
addressing the fundamental issues in LFS, which are snowball effect of wandering
tree and high cleaning overhead.
Since a NAND flash memory-based storage device shows different characteristic
according to its internal geometry or flash memory management scheme, namely FTL,
F2FS and its tools support various parameters not only for configuring on-disk
layout, but also for selecting allocation and cleaning algorithms.
The following git tree provides the file system formatting tool (mkfs.f2fs),
a consistency checking tool (fsck.f2fs), and a debugging tool (dump.f2fs).
- git://git.kernel.org/pub/scm/linux/kernel/git/jaegeuk/f2fs-tools.git
For reporting bugs and sending patches, please use the following mailing list:
- linux-f2fs-devel@lists.sourceforge.net
Background and Design issues
============================
Log-structured File System (LFS)
--------------------------------
"A log-structured file system writes all modifications to disk sequentially in
a log-like structure, thereby speeding up both file writing and crash recovery.
The log is the only structure on disk; it contains indexing information so that
files can be read back from the log efficiently. In order to maintain large free
areas on disk for fast writing, we divide the log into segments and use a
segment cleaner to compress the live information from heavily fragmented
segments." from Rosenblum, M. and Ousterhout, J. K., 1992, "The design and
implementation of a log-structured file system", ACM Trans. Computer Systems
10, 1, 26–52.
Wandering Tree Problem
----------------------
In LFS, when a file data is updated and written to the end of log, its direct
pointer block is updated due to the changed location. Then the indirect pointer
block is also updated due to the direct pointer block update. In this manner,
the upper index structures such as inode, inode map, and checkpoint block are
also updated recursively. This problem is called as wandering tree problem [1],
and in order to enhance the performance, it should eliminate or relax the update
propagation as much as possible.
[1] Bityutskiy, A. 2005. JFFS3 design issues. http://www.linux-mtd.infradead.org/
Cleaning Overhead
-----------------
Since LFS is based on out-of-place writes, it produces so many obsolete blocks
scattered across the whole storage. In order to serve new empty log space, it
needs to reclaim these obsolete blocks seamlessly to users. This job is called
as a cleaning process.
The process consists of three operations as follows.
1. A victim segment is selected through referencing segment usage table.
2. It loads parent index structures of all the data in the victim identified by
segment summary blocks.
3. It checks the cross-reference between the data and its parent index structure.
4. It moves valid data selectively.
This cleaning job may cause unexpected long delays, so the most important goal
is to hide the latencies to users. And also definitely, it should reduce the
amount of valid data to be moved, and move them quickly as well.
Key Features
============
Flash Awareness
---------------
- Enlarge the random write area for better performance, but provide the high
spatial locality
- Align FS data structures to the operational units in FTL as best efforts
Wandering Tree Problem
----------------------
- Use a term, “node”, that represents inodes as well as various pointer blocks
- Introduce Node Address Table (NAT) containing the locations of all the “node”
blocks; this will cut off the update propagation.
Cleaning Overhead
-----------------
- Support a background cleaning process
- Support greedy and cost-benefit algorithms for victim selection policies
- Support multi-head logs for static/dynamic hot and cold data separation
- Introduce adaptive logging for efficient block allocation
Mount Options
=============
======================== ============================================================
background_gc=%s Turn on/off cleaning operations, namely garbage
collection, triggered in background when I/O subsystem is
idle. If background_gc=on, it will turn on the garbage
collection and if background_gc=off, garbage collection
will be turned off. If background_gc=sync, it will turn
on synchronous garbage collection running in background.
Default value for this option is on. So garbage
collection is on by default.
gc_merge When background_gc is on, this option can be enabled to
let background GC thread to handle foreground GC requests,
it can eliminate the sluggish issue caused by slow foreground
GC operation when GC is triggered from a process with limited
I/O and CPU resources.
nogc_merge Disable GC merge feature.
disable_roll_forward Disable the roll-forward recovery routine
norecovery Disable the roll-forward recovery routine, mounted read-
only (i.e., -o ro,disable_roll_forward)
discard/nodiscard Enable/disable real-time discard in f2fs, if discard is
enabled, f2fs will issue discard/TRIM commands when a
segment is cleaned.
no_heap Disable heap-style segment allocation which finds free
segments for data from the beginning of main area, while
for node from the end of main area.
nouser_xattr Disable Extended User Attributes. Note: xattr is enabled
by default if CONFIG_F2FS_FS_XATTR is selected.
noacl Disable POSIX Access Control List. Note: acl is enabled
by default if CONFIG_F2FS_FS_POSIX_ACL is selected.
active_logs=%u Support configuring the number of active logs. In the
current design, f2fs supports only 2, 4, and 6 logs.
Default number is 6.
disable_ext_identify Disable the extension list configured by mkfs, so f2fs
is not aware of cold files such as media files.
inline_xattr Enable the inline xattrs feature.
noinline_xattr Disable the inline xattrs feature.
inline_xattr_size=%u Support configuring inline xattr size, it depends on
flexible inline xattr feature.
inline_data Enable the inline data feature: Newly created small (<~3.4k)
files can be written into inode block.
inline_dentry Enable the inline dir feature: data in newly created
directory entries can be written into inode block. The
space of inode block which is used to store inline
dentries is limited to ~3.4k.
noinline_dentry Disable the inline dentry feature.
flush_merge Merge concurrent cache_flush commands as much as possible
to eliminate redundant command issues. If the underlying
device handles the cache_flush command relatively slowly,
recommend to enable this option.
nobarrier This option can be used if underlying storage guarantees
its cached data should be written to the novolatile area.
If this option is set, no cache_flush commands are issued
but f2fs still guarantees the write ordering of all the
data writes.
fastboot This option is used when a system wants to reduce mount
time as much as possible, even though normal performance
can be sacrificed.
extent_cache Enable an extent cache based on rb-tree, it can cache
as many as extent which map between contiguous logical
address and physical address per inode, resulting in
increasing the cache hit ratio. Set by default.
noextent_cache Disable an extent cache based on rb-tree explicitly, see
the above extent_cache mount option.
noinline_data Disable the inline data feature, inline data feature is
enabled by default.
data_flush Enable data flushing before checkpoint in order to
persist data of regular and symlink.
reserve_root=%d Support configuring reserved space which is used for
allocation from a privileged user with specified uid or
gid, unit: 4KB, the default limit is 0.2% of user blocks.
resuid=%d The user ID which may use the reserved blocks.
resgid=%d The group ID which may use the reserved blocks.
fault_injection=%d Enable fault injection in all supported types with
specified injection rate.
fault_type=%d Support configuring fault injection type, should be
enabled with fault_injection option, fault type value
is shown below, it supports single or combined type.
=================== ===========
Type_Name Type_Value
=================== ===========
FAULT_KMALLOC 0x000000001
FAULT_KVMALLOC 0x000000002
FAULT_PAGE_ALLOC 0x000000004
FAULT_PAGE_GET 0x000000008
FAULT_ALLOC_NID 0x000000020
FAULT_ORPHAN 0x000000040
FAULT_BLOCK 0x000000080
FAULT_DIR_DEPTH 0x000000100
FAULT_EVICT_INODE 0x000000200
FAULT_TRUNCATE 0x000000400
FAULT_READ_IO 0x000000800
FAULT_CHECKPOINT 0x000001000
FAULT_DISCARD 0x000002000
FAULT_WRITE_IO 0x000004000
=================== ===========
mode=%s Control block allocation mode which supports "adaptive"
and "lfs". In "lfs" mode, there should be no random
writes towards main area.
io_bits=%u Set the bit size of write IO requests. It should be set
with "mode=lfs".
usrquota Enable plain user disk quota accounting.
grpquota Enable plain group disk quota accounting.
prjquota Enable plain project quota accounting.
usrjquota=<file> Appoint specified file and type during mount, so that quota
grpjquota=<file> information can be properly updated during recovery flow,
prjjquota=<file> <quota file>: must be in root directory;
jqfmt=<quota type> <quota type>: [vfsold,vfsv0,vfsv1].
offusrjquota Turn off user journalled quota.
offgrpjquota Turn off group journalled quota.
offprjjquota Turn off project journalled quota.
quota Enable plain user disk quota accounting.
noquota Disable all plain disk quota option.
whint_mode=%s Control which write hints are passed down to block
layer. This supports "off", "user-based", and
"fs-based". In "off" mode (default), f2fs does not pass
down hints. In "user-based" mode, f2fs tries to pass
down hints given by users. And in "fs-based" mode, f2fs
passes down hints with its policy.
alloc_mode=%s Adjust block allocation policy, which supports "reuse"
and "default".
fsync_mode=%s Control the policy of fsync. Currently supports "posix",
"strict", and "nobarrier". In "posix" mode, which is
default, fsync will follow POSIX semantics and does a
light operation to improve the filesystem performance.
In "strict" mode, fsync will be heavy and behaves in line
with xfs, ext4 and btrfs, where xfstest generic/342 will
pass, but the performance will regress. "nobarrier" is
based on "posix", but doesn't issue flush command for
non-atomic files likewise "nobarrier" mount option.
fscrypt: support test_dummy_encryption=v2 v1 encryption policies are deprecated in favor of v2, and some new features (e.g. encryption+casefolding) are only being added for v2. Therefore, the "test_dummy_encryption" mount option (which is used for encryption I/O testing with xfstests) needs to support v2 policies. To do this, extend its syntax to be "test_dummy_encryption=v1" or "test_dummy_encryption=v2". The existing "test_dummy_encryption" (no argument) also continues to be accepted, to specify the default setting -- currently v1, but the next patch changes it to v2. To cleanly support both v1 and v2 while also making it easy to support specifying other encryption settings in the future (say, accepting "$contents_mode:$filenames_mode:v2"), make ext4 and f2fs maintain a pointer to the dummy fscrypt_context rather than using mount flags. To avoid concurrency issues, don't allow test_dummy_encryption to be set or changed during a remount. (The former restriction is new, but xfstests doesn't run into it, so no one should notice.) Tested with 'gce-xfstests -c {ext4,f2fs}/encrypt -g auto'. On ext4, there are two regressions, both of which are test bugs: ext4/023 and ext4/028 fail because they set an xattr and expect it to be stored inline, but the increase in size of the fscrypt_context from 24 to 40 bytes causes this xattr to be spilled into an external block. Link: https://lore.kernel.org/r/20200512233251.118314-4-ebiggers@kernel.org Acked-by: Jaegeuk Kim <jaegeuk@kernel.org> Reviewed-by: Theodore Ts'o <tytso@mit.edu> Signed-off-by: Eric Biggers <ebiggers@google.com>
2020-05-13 02:32:50 +03:00
test_dummy_encryption
test_dummy_encryption=%s
Enable dummy encryption, which provides a fake fscrypt
context. The fake fscrypt context is used by xfstests.
The argument may be either "v1" or "v2", in order to
select the corresponding fscrypt policy version.
checkpoint=%s[:%u[%]] Set to "disable" to turn off checkpointing. Set to "enable"
to reenable checkpointing. Is enabled by default. While
disabled, any unmounting or unexpected shutdowns will cause
the filesystem contents to appear as they did when the
filesystem was mounted with that option.
While mounting with checkpoint=disabled, the filesystem must
run garbage collection to ensure that all available space can
be used. If this takes too much time, the mount may return
EAGAIN. You may optionally add a value to indicate how much
of the disk you would be willing to temporarily give up to
avoid additional garbage collection. This can be given as a
number of blocks, or as a percent. For instance, mounting
with checkpoint=disable:100% would always succeed, but it may
hide up to all remaining free space. The actual space that
would be unusable can be viewed at /sys/fs/f2fs/<disk>/unusable
This space is reclaimed once checkpoint=enable.
f2fs: introduce checkpoint_merge mount option We've added a new mount options, "checkpoint_merge" and "nocheckpoint_merge", which creates a kernel daemon and makes it to merge concurrent checkpoint requests as much as possible to eliminate redundant checkpoint issues. Plus, we can eliminate the sluggish issue caused by slow checkpoint operation when the checkpoint is done in a process context in a cgroup having low i/o budget and cpu shares. To make this do better, we set the default i/o priority of the kernel daemon to "3", to give one higher priority than other kernel threads. The below verification result explains this. The basic idea has come from https://opensource.samsung.com. [Verification] Android Pixel Device(ARM64, 7GB RAM, 256GB UFS) Create two I/O cgroups (fg w/ weight 100, bg w/ wight 20) Set "strict_guarantees" to "1" in BFQ tunables In "fg" cgroup, - thread A => trigger 1000 checkpoint operations "for i in `seq 1 1000`; do touch test_dir1/file; fsync test_dir1; done" - thread B => gererating async. I/O "fio --rw=write --numjobs=1 --bs=128k --runtime=3600 --time_based=1 --filename=test_img --name=test" In "bg" cgroup, - thread C => trigger repeated checkpoint operations "echo $$ > /dev/blkio/bg/tasks; while true; do touch test_dir2/file; fsync test_dir2; done" We've measured thread A's execution time. [ w/o patch ] Elapsed Time: Avg. 68 seconds [ w/ patch ] Elapsed Time: Avg. 48 seconds Reported-by: kernel test robot <lkp@intel.com> Reported-by: Dan Carpenter <dan.carpenter@oracle.com> [Jaegeuk Kim: fix the return value in f2fs_start_ckpt_thread, reported by Dan] Signed-off-by: Daeho Jeong <daehojeong@google.com> Signed-off-by: Sungjong Seo <sj1557.seo@samsung.com> Reviewed-by: Chao Yu <yuchao0@huawei.com> Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>
2021-01-19 03:00:42 +03:00
checkpoint_merge When checkpoint is enabled, this can be used to create a kernel
daemon and make it to merge concurrent checkpoint requests as
much as possible to eliminate redundant checkpoint issues. Plus,
we can eliminate the sluggish issue caused by slow checkpoint
operation when the checkpoint is done in a process context in
a cgroup having low i/o budget and cpu shares. To make this
do better, we set the default i/o priority of the kernel daemon
to "3", to give one higher priority than other kernel threads.
This is the same way to give a I/O priority to the jbd2
journaling thread of ext4 filesystem.
nocheckpoint_merge Disable checkpoint merge feature.
compress_algorithm=%s Control compress algorithm, currently f2fs supports "lzo",
"lz4", "zstd" and "lzo-rle" algorithm.
compress_algorithm=%s:%d Control compress algorithm and its compress level, now, only
"lz4" and "zstd" support compress level config.
algorithm level range
lz4 3 - 16
zstd 1 - 22
compress_log_size=%u Support configuring compress cluster size, the size will
be 4KB * (1 << %u), 16KB is minimum size, also it's
default size.
compress_extension=%s Support adding specified extension, so that f2fs can enable
compression on those corresponding files, e.g. if all files
with '.ext' has high compression rate, we can set the '.ext'
on compression extension list and enable compression on
these file by default rather than to enable it via ioctl.
For other files, we can still enable compression via ioctl.
f2fs-for-5.9-rc1 In this round, we've added two small interfaces, 1) GC_URGENT_LOW mode for performance, and 2) F2FS_IOC_SEC_TRIM_FILE ioctl for security. The new GC mode allows Android to run some lower priority GCs in background, while new ioctl discards user information without race condition when the account is removed. In addition, some patches were merged to address latency-related issues. We've fixed some compression-related bug fixes as well as edge race conditions. Enhancement: - add GC_URGENT_LOW mode in gc_urgent - introduce F2FS_IOC_SEC_TRIM_FILE ioctl - bypass racy readahead to improve read latencies - shrink node_write lock coverage to avoid long latency Bug fix: - fix missing compression flag control, i_size, and mount option - fix deadlock between quota writes and checkpoint - remove inode eviction path in synchronous path to avoid deadlock - fix to wait GCed compressed page writeback - fix a kernel panic in f2fs_is_compressed_page - check page dirty status before writeback - wait page writeback before update in node page write flow - fix a race condition between f2fs_write_end_io and f2fs_del_fsync_node_entry We've added some minor sanity checks and refactored trivial code blocks for better readability and debugging information. -----BEGIN PGP SIGNATURE----- iQIzBAABCgAdFiEE00UqedjCtOrGVvQiQBSofoJIUNIFAl8xhqMACgkQQBSofoJI UNLYgA//WMoOqBACDuOWwYmgQ8oq4vrH2LOwssZF9/77vEfaHKc+TSq1il54lcUl MPEx7FK54CnfT8VLLR5ByobZFyH9FFeAw4FN4LBhcfE8jh8ysAGjeoZjwfcmJF6R cVKtn8ltUpgH3IEUuPjTiKkVNHfVJxuuL3zHbg1CEl+AkR6NJ/U9kNLwf7ZgPWq2 I0qwyXRlUIEChhyPZB+Y6RsdGjkeievKld56DMCgG73f4yHRO/yBcrfsN875sGdM ALL+mYiunMT6aXcfoiQiAjeImoNajuflI6Zso2Sk8Vl6sBj0QwAuEBF5x1Z5e1mt YVYNuC4ucqsDBKpOqtsPP0MFTC2T5Rr9wWXjqv+9TjN7zvJ8xx+zDWtQxvI2bpqB 4ZRxaJP45aThLYh/SEYDmj+ppyPtfLDeG0HzUkwMmuopf9eg+kxGPjBsZewgkCKg kmMKU0P7deGlkrWLUcz2vm0Lso+ieGm0IeLOQl9/rOLu3IQQFia0Vla7dLDgqF0P sz+udIiBztC3JPEmEZhfayA6P6e1TyWQUdquL08jp+DZD17gPqcaZDhHr62U5rmK 7zoiZqkR03SbNaFhBhhoVOaAVcAnF0pSIgqzkCa3dVXxp1QV+JfD9CGR9NFyiIqB HK5RPFskIUCg0K2LSaAKbyoFWa/fJ8ZD8/CbFWcnXfWzoaaSkmc= =PjaF -----END PGP SIGNATURE----- Merge tag 'f2fs-for-5.9-rc1' of git://git.kernel.org/pub/scm/linux/kernel/git/jaegeuk/f2fs Pull f2fs updates from Jaegeuk Kim: "In this round, we've added two small interfaces: (a) GC_URGENT_LOW mode for performance and (b) F2FS_IOC_SEC_TRIM_FILE ioctl for security. The new GC mode allows Android to run some lower priority GCs in background, while new ioctl discards user information without race condition when the account is removed. In addition, some patches were merged to address latency-related issues. We've fixed some compression-related bug fixes as well as edge race conditions. Enhancements: - add GC_URGENT_LOW mode in gc_urgent - introduce F2FS_IOC_SEC_TRIM_FILE ioctl - bypass racy readahead to improve read latencies - shrink node_write lock coverage to avoid long latency Bug fixes: - fix missing compression flag control, i_size, and mount option - fix deadlock between quota writes and checkpoint - remove inode eviction path in synchronous path to avoid deadlock - fix to wait GCed compressed page writeback - fix a kernel panic in f2fs_is_compressed_page - check page dirty status before writeback - wait page writeback before update in node page write flow - fix a race condition between f2fs_write_end_io and f2fs_del_fsync_node_entry We've added some minor sanity checks and refactored trivial code blocks for better readability and debugging information" * tag 'f2fs-for-5.9-rc1' of git://git.kernel.org/pub/scm/linux/kernel/git/jaegeuk/f2fs: (52 commits) f2fs: prepare a waiter before entering io_schedule f2fs: update_sit_entry: Make the judgment condition of f2fs_bug_on more intuitive f2fs: replace test_and_set/clear_bit() with set/clear_bit() f2fs: make file immutable even if releasing zero compression block f2fs: compress: disable compression mount option if compression is off f2fs: compress: add sanity check during compressed cluster read f2fs: use macro instead of f2fs verity version f2fs: fix deadlock between quota writes and checkpoint f2fs: correct comment of f2fs_exist_written_data f2fs: compress: delay temp page allocation f2fs: compress: fix to update isize when overwriting compressed file f2fs: space related cleanup f2fs: fix use-after-free issue f2fs: Change the type of f2fs_flush_inline_data() to void f2fs: add F2FS_IOC_SEC_TRIM_FILE ioctl f2fs: should avoid inode eviction in synchronous path f2fs: segment.h: delete a duplicated word f2fs: compress: fix to avoid memory leak on cc->cpages f2fs: use generic names for generic ioctls f2fs: don't keep meta inode pages used for compressed block migration ...
2020-08-11 04:33:22 +03:00
Note that, there is one reserved special extension '*', it
can be set to enable compression for all files.
compress_chksum Support verifying chksum of raw data in compressed cluster.
compress_mode=%s Control file compression mode. This supports "fs" and "user"
modes. In "fs" mode (default), f2fs does automatic compression
on the compression enabled files. In "user" mode, f2fs disables
the automaic compression and gives the user discretion of
choosing the target file and the timing. The user can do manual
compression/decompression on the compression enabled files using
ioctls.
compress_cache Support to use address space of a filesystem managed inode to
cache compressed block, in order to improve cache hit ratio of
random read.
It's been a busy cycle for documentation - hopefully the busiest for a while to come. Changes include: - Some new Chinese translations - Progress on the battle against double words words and non-HTTPS URLs - Some block-mq documentation - More RST conversions from Mauro. At this point, that task is essentially complete, so we shouldn't see this kind of churn again for a while. Unless we decide to switch to asciidoc or something...:) - Lots of typo fixes, warning fixes, and more. -----BEGIN PGP SIGNATURE----- iQFDBAABCAAtFiEEIw+MvkEiF49krdp9F0NaE2wMflgFAl8oVkwPHGNvcmJldEBs d24ubmV0AAoJEBdDWhNsDH5YoW8H/jJ/xnXFn7tkgVPQAlL3k5HCnK7A5nDP9RVR cg1pTx1cEFdjzxPlJyExU6/v+AImOvtweHXC+JDK7YcJ6XFUNYXJI3LxL5KwUXbY BL/xRFszDSXH2C7SJF5GECcFYp01e/FWSLN3yWAh+g+XwsKiTJ8q9+CoIDkHfPGO 7oQsHKFu6s36Af0LfSgxk4sVB7EJbo8e4psuPsP5SUrl+oXRO43Put0rXkR4yJoH 9oOaB51Do5fZp8I4JVAqGXvpXoExyLMO4yw0mASm6YSZ3KyjR8Fae+HD9Cq4ZuwY 0uzb9K+9NEhqbfwtyBsi99S64/6Zo/MonwKwevZuhtsDTK4l4iU= =JQLZ -----END PGP SIGNATURE----- Merge tag 'docs-5.9' of git://git.lwn.net/linux Pull documentation updates from Jonathan Corbet: "It's been a busy cycle for documentation - hopefully the busiest for a while to come. Changes include: - Some new Chinese translations - Progress on the battle against double words words and non-HTTPS URLs - Some block-mq documentation - More RST conversions from Mauro. At this point, that task is essentially complete, so we shouldn't see this kind of churn again for a while. Unless we decide to switch to asciidoc or something...:) - Lots of typo fixes, warning fixes, and more" * tag 'docs-5.9' of git://git.lwn.net/linux: (195 commits) scripts/kernel-doc: optionally treat warnings as errors docs: ia64: correct typo mailmap: add entry for <alobakin@marvell.com> doc/zh_CN: add cpu-load Chinese version Documentation/admin-guide: tainted-kernels: fix spelling mistake MAINTAINERS: adjust kprobes.rst entry to new location devices.txt: document rfkill allocation PCI: correct flag name docs: filesystems: vfs: correct flag name docs: filesystems: vfs: correct sync_mode flag names docs: path-lookup: markup fixes for emphasis docs: path-lookup: more markup fixes docs: path-lookup: fix HTML entity mojibake CREDITS: Replace HTTP links with HTTPS ones docs: process: Add an example for creating a fixes tag doc/zh_CN: add Chinese translation prefer section doc/zh_CN: add clearing-warn-once Chinese version doc/zh_CN: add admin-guide index doc:it_IT: process: coding-style.rst: Correct __maybe_unused compiler label futex: MAINTAINERS: Re-add selftests directory ...
2020-08-05 08:47:54 +03:00
inlinecrypt When possible, encrypt/decrypt the contents of encrypted
files using the blk-crypto framework rather than
filesystem-layer encryption. This allows the use of
inline encryption hardware. The on-disk format is
unaffected. For more details, see
Documentation/block/inline-encryption.rst.
f2fs: support age threshold based garbage collection There are several issues in current background GC algorithm: - valid blocks is one of key factors during cost overhead calculation, so if segment has less valid block, however even its age is young or it locates hot segment, CB algorithm will still choose the segment as victim, it's not appropriate. - GCed data/node will go to existing logs, no matter in-there datas' update frequency is the same or not, it may mix hot and cold data again. - GC alloctor mainly use LFS type segment, it will cost free segment more quickly. This patch introduces a new algorithm named age threshold based garbage collection to solve above issues, there are three steps mainly: 1. select a source victim: - set an age threshold, and select candidates beased threshold: e.g. 0 means youngest, 100 means oldest, if we set age threshold to 80 then select dirty segments which has age in range of [80, 100] as candiddates; - set candidate_ratio threshold, and select candidates based the ratio, so that we can shrink candidates to those oldest segments; - select target segment with fewest valid blocks in order to migrate blocks with minimum cost; 2. select a target victim: - select candidates beased age threshold; - set candidate_radius threshold, search candidates whose age is around source victims, searching radius should less than the radius threshold. - select target segment with most valid blocks in order to avoid migrating current target segment. 3. merge valid blocks from source victim into target victim with SSR alloctor. Test steps: - create 160 dirty segments: * half of them have 128 valid blocks per segment * left of them have 384 valid blocks per segment - run background GC Benefit: GC count and block movement count both decrease obviously: - Before: - Valid: 86 - Dirty: 1 - Prefree: 11 - Free: 6001 (6001) GC calls: 162 (BG: 220) - data segments : 160 (160) - node segments : 2 (2) Try to move 41454 blocks (BG: 41454) - data blocks : 40960 (40960) - node blocks : 494 (494) IPU: 0 blocks SSR: 0 blocks in 0 segments LFS: 41364 blocks in 81 segments - After: - Valid: 87 - Dirty: 0 - Prefree: 4 - Free: 6008 (6008) GC calls: 75 (BG: 76) - data segments : 74 (74) - node segments : 1 (1) Try to move 12813 blocks (BG: 12813) - data blocks : 12544 (12544) - node blocks : 269 (269) IPU: 0 blocks SSR: 12032 blocks in 77 segments LFS: 855 blocks in 2 segments Signed-off-by: Chao Yu <yuchao0@huawei.com> [Jaegeuk Kim: fix a bug along with pinfile in-mem segment & clean up] Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>
2020-08-04 16:14:49 +03:00
atgc Enable age-threshold garbage collection, it provides high
effectiveness and efficiency on background GC.
======================== ============================================================
Debugfs Entries
===============
/sys/kernel/debug/f2fs/ contains information about all the partitions mounted as
f2fs. Each file shows the whole f2fs information.
/sys/kernel/debug/f2fs/status includes:
- major file system information managed by f2fs currently
- average SIT information about whole segments
- current memory footprint consumed by f2fs.
Sysfs Entries
=============
Information about mounted f2fs file systems can be found in
/sys/fs/f2fs. Each mounted filesystem will have a directory in
/sys/fs/f2fs based on its device name (i.e., /sys/fs/f2fs/sda).
The files in each per-device directory are shown in table below.
Files in /sys/fs/f2fs/<devname>
(see also Documentation/ABI/testing/sysfs-fs-f2fs)
f2fs: include charset encoding information in the superblock Add charset encoding to f2fs to support casefolding. It is modeled after the same feature introduced in commit c83ad55eaa91 ("ext4: include charset encoding information in the superblock") Currently this is not compatible with encryption, similar to the current ext4 imlpementation. This will change in the future. >From the ext4 patch: """ The s_encoding field stores a magic number indicating the encoding format and version used globally by file and directory names in the filesystem. The s_encoding_flags defines policies for using the charset encoding, like how to handle invalid sequences. The magic number is mapped to the exact charset table, but the mapping is specific to ext4. Since we don't have any commitment to support old encodings, the only encoding I am supporting right now is utf8-12.1.0. The current implementation prevents the user from enabling encoding and per-directory encryption on the same filesystem at the same time. The incompatibility between these features lies in how we do efficient directory searches when we cannot be sure the encryption of the user provided fname will match the actual hash stored in the disk without decrypting every directory entry, because of normalization cases. My quickest solution is to simply block the concurrent use of these features for now, and enable it later, once we have a better solution. """ Signed-off-by: Daniel Rosenberg <drosen@google.com> Reviewed-by: Chao Yu <yuchao0@huawei.com> Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>
2019-07-24 02:05:28 +03:00
Usage
=====
1. Download userland tools and compile them.
2. Skip, if f2fs was compiled statically inside kernel.
Otherwise, insert the f2fs.ko module::
# insmod f2fs.ko
3. Create a directory to use when mounting::
# mkdir /mnt/f2fs
4. Format the block device, and then mount as f2fs::
# mkfs.f2fs -l label /dev/block_device
# mount -t f2fs /dev/block_device /mnt/f2fs
mkfs.f2fs
---------
The mkfs.f2fs is for the use of formatting a partition as the f2fs filesystem,
which builds a basic on-disk layout.
The quick options consist of:
=============== ===========================================================
``-l [label]`` Give a volume label, up to 512 unicode name.
``-a [0 or 1]`` Split start location of each area for heap-based allocation.
1 is set by default, which performs this.
``-o [int]`` Set overprovision ratio in percent over volume size.
5 is set by default.
``-s [int]`` Set the number of segments per section.
1 is set by default.
``-z [int]`` Set the number of sections per zone.
1 is set by default.
``-e [str]`` Set basic extension list. e.g. "mp3,gif,mov"
``-t [0 or 1]`` Disable discard command or not.
1 is set by default, which conducts discard.
=============== ===========================================================
Note: please refer to the manpage of mkfs.f2fs(8) to get full option list.
fsck.f2fs
---------
The fsck.f2fs is a tool to check the consistency of an f2fs-formatted
partition, which examines whether the filesystem metadata and user-made data
are cross-referenced correctly or not.
Note that, initial version of the tool does not fix any inconsistency.
The quick options consist of::
-d debug level [default:0]
Note: please refer to the manpage of fsck.f2fs(8) to get full option list.
dump.f2fs
---------
The dump.f2fs shows the information of specific inode and dumps SSA and SIT to
file. Each file is dump_ssa and dump_sit.
The dump.f2fs is used to debug on-disk data structures of the f2fs filesystem.
It shows on-disk inode information recognized by a given inode number, and is
able to dump all the SSA and SIT entries into predefined files, ./dump_ssa and
./dump_sit respectively.
The options consist of::
-d debug level [default:0]
-i inode no (hex)
-s [SIT dump segno from #1~#2 (decimal), for all 0~-1]
-a [SSA dump segno from #1~#2 (decimal), for all 0~-1]
Examples::
# dump.f2fs -i [ino] /dev/sdx
# dump.f2fs -s 0~-1 /dev/sdx (SIT dump)
# dump.f2fs -a 0~-1 /dev/sdx (SSA dump)
Note: please refer to the manpage of dump.f2fs(8) to get full option list.
sload.f2fs
----------
The sload.f2fs gives a way to insert files and directories in the exisiting disk
image. This tool is useful when building f2fs images given compiled files.
Note: please refer to the manpage of sload.f2fs(8) to get full option list.
resize.f2fs
-----------
The resize.f2fs lets a user resize the f2fs-formatted disk image, while preserving
all the files and directories stored in the image.
Note: please refer to the manpage of resize.f2fs(8) to get full option list.
defrag.f2fs
-----------
The defrag.f2fs can be used to defragment scattered written data as well as
filesystem metadata across the disk. This can improve the write speed by giving
more free consecutive space.
Note: please refer to the manpage of defrag.f2fs(8) to get full option list.
f2fs_io
-------
The f2fs_io is a simple tool to issue various filesystem APIs as well as
f2fs-specific ones, which is very useful for QA tests.
Note: please refer to the manpage of f2fs_io(8) to get full option list.
Design
======
On-disk Layout
--------------
F2FS divides the whole volume into a number of segments, each of which is fixed
to 2MB in size. A section is composed of consecutive segments, and a zone
consists of a set of sections. By default, section and zone sizes are set to one
segment size identically, but users can easily modify the sizes by mkfs.
F2FS splits the entire volume into six areas, and all the areas except superblock
consist of multiple segments as described below::
align with the zone size <-|
|-> align with the segment size
_________________________________________________________________________
| | | Segment | Node | Segment | |
| Superblock | Checkpoint | Info. | Address | Summary | Main |
| (SB) | (CP) | Table (SIT) | Table (NAT) | Area (SSA) | |
|____________|_____2______|______N______|______N______|______N_____|__N___|
. .
. .
. .
._________________________________________.
|_Segment_|_..._|_Segment_|_..._|_Segment_|
. .
._________._________
|_section_|__...__|_
. .
.________.
|__zone__|
- Superblock (SB)
It is located at the beginning of the partition, and there exist two copies
to avoid file system crash. It contains basic partition information and some
default parameters of f2fs.
- Checkpoint (CP)
It contains file system information, bitmaps for valid NAT/SIT sets, orphan
inode lists, and summary entries of current active segments.
- Segment Information Table (SIT)
It contains segment information such as valid block count and bitmap for the
validity of all the blocks.
- Node Address Table (NAT)
It is composed of a block address table for all the node blocks stored in
Main area.
- Segment Summary Area (SSA)
It contains summary entries which contains the owner information of all the
data and node blocks stored in Main area.
- Main Area
It contains file and directory data including their indices.
In order to avoid misalignment between file system and flash-based storage, F2FS
aligns the start block address of CP with the segment size. Also, it aligns the
start block address of Main area with the zone size by reserving some segments
in SSA area.
Reference the following survey for additional technical details.
https://wiki.linaro.org/WorkingGroups/Kernel/Projects/FlashCardSurvey
File System Metadata Structure
------------------------------
F2FS adopts the checkpointing scheme to maintain file system consistency. At
mount time, F2FS first tries to find the last valid checkpoint data by scanning
CP area. In order to reduce the scanning time, F2FS uses only two copies of CP.
One of them always indicates the last valid data, which is called as shadow copy
mechanism. In addition to CP, NAT and SIT also adopt the shadow copy mechanism.
For file system consistency, each CP points to which NAT and SIT copies are
valid, as shown as below::
+--------+----------+---------+
| CP | SIT | NAT |
+--------+----------+---------+
. . . .
. . . .
. . . .
+-------+-------+--------+--------+--------+--------+
| CP #0 | CP #1 | SIT #0 | SIT #1 | NAT #0 | NAT #1 |
+-------+-------+--------+--------+--------+--------+
| ^ ^
| | |
`----------------------------------------'
Index Structure
---------------
The key data structure to manage the data locations is a "node". Similar to
traditional file structures, F2FS has three types of node: inode, direct node,
indirect node. F2FS assigns 4KB to an inode block which contains 923 data block
indices, two direct node pointers, two indirect node pointers, and one double
indirect node pointer as described below. One direct node block contains 1018
data blocks, and one indirect node block contains also 1018 node blocks. Thus,
one inode block (i.e., a file) covers::
4KB * (923 + 2 * 1018 + 2 * 1018 * 1018 + 1018 * 1018 * 1018) := 3.94TB.
Inode block (4KB)
|- data (923)
|- direct node (2)
| `- data (1018)
|- indirect node (2)
| `- direct node (1018)
| `- data (1018)
`- double indirect node (1)
`- indirect node (1018)
`- direct node (1018)
`- data (1018)
Note that all the node blocks are mapped by NAT which means the location of
each node is translated by the NAT table. In the consideration of the wandering
tree problem, F2FS is able to cut off the propagation of node updates caused by
leaf data writes.
Directory Structure
-------------------
A directory entry occupies 11 bytes, which consists of the following attributes.
- hash hash value of the file name
- ino inode number
- len the length of file name
- type file type such as directory, symlink, etc
A dentry block consists of 214 dentry slots and file names. Therein a bitmap is
used to represent whether each dentry is valid or not. A dentry block occupies
4KB with the following composition.
::
Dentry Block(4 K) = bitmap (27 bytes) + reserved (3 bytes) +
dentries(11 * 214 bytes) + file name (8 * 214 bytes)
[Bucket]
+--------------------------------+
|dentry block 1 | dentry block 2 |
+--------------------------------+
. .
. .
. [Dentry Block Structure: 4KB] .
+--------+----------+----------+------------+
| bitmap | reserved | dentries | file names |
+--------+----------+----------+------------+
[Dentry Block: 4KB] . .
. .
. .
+------+------+-----+------+
| hash | ino | len | type |
+------+------+-----+------+
[Dentry Structure: 11 bytes]
F2FS implements multi-level hash tables for directory structure. Each level has
a hash table with dedicated number of hash buckets as shown below. Note that
"A(2B)" means a bucket includes 2 data blocks.
::
----------------------
A : bucket
B : block
N : MAX_DIR_HASH_DEPTH
----------------------
level #0 | A(2B)
|
level #1 | A(2B) - A(2B)
|
level #2 | A(2B) - A(2B) - A(2B) - A(2B)
. | . . . .
level #N/2 | A(2B) - A(2B) - A(2B) - A(2B) - A(2B) - ... - A(2B)
. | . . . .
level #N | A(4B) - A(4B) - A(4B) - A(4B) - A(4B) - ... - A(4B)
The number of blocks and buckets are determined by::
,- 2, if n < MAX_DIR_HASH_DEPTH / 2,
# of blocks in level #n = |
`- 4, Otherwise
,- 2^(n + dir_level),
| if n + dir_level < MAX_DIR_HASH_DEPTH / 2,
# of buckets in level #n = |
`- 2^((MAX_DIR_HASH_DEPTH / 2) - 1),
Otherwise
When F2FS finds a file name in a directory, at first a hash value of the file
name is calculated. Then, F2FS scans the hash table in level #0 to find the
dentry consisting of the file name and its inode number. If not found, F2FS
scans the next hash table in level #1. In this way, F2FS scans hash tables in
each levels incrementally from 1 to N. In each level F2FS needs to scan only
one bucket determined by the following equation, which shows O(log(# of files))
complexity::
bucket number to scan in level #n = (hash value) % (# of buckets in level #n)
In the case of file creation, F2FS finds empty consecutive slots that cover the
file name. F2FS searches the empty slots in the hash tables of whole levels from
1 to N in the same way as the lookup operation.
The following figure shows an example of two cases holding children::
--------------> Dir <--------------
| |
child child
child - child [hole] - child
child - child - child [hole] - [hole] - child
Case 1: Case 2:
Number of children = 6, Number of children = 3,
File size = 7 File size = 7
Default Block Allocation
------------------------
At runtime, F2FS manages six active logs inside "Main" area: Hot/Warm/Cold node
and Hot/Warm/Cold data.
- Hot node contains direct node blocks of directories.
- Warm node contains direct node blocks except hot node blocks.
- Cold node contains indirect node blocks
- Hot data contains dentry blocks
- Warm data contains data blocks except hot and cold data blocks
- Cold data contains multimedia data or migrated data blocks
LFS has two schemes for free space management: threaded log and copy-and-compac-
tion. The copy-and-compaction scheme which is known as cleaning, is well-suited
for devices showing very good sequential write performance, since free segments
are served all the time for writing new data. However, it suffers from cleaning
overhead under high utilization. Contrarily, the threaded log scheme suffers
from random writes, but no cleaning process is needed. F2FS adopts a hybrid
scheme where the copy-and-compaction scheme is adopted by default, but the
policy is dynamically changed to the threaded log scheme according to the file
system status.
In order to align F2FS with underlying flash-based storage, F2FS allocates a
segment in a unit of section. F2FS expects that the section size would be the
same as the unit size of garbage collection in FTL. Furthermore, with respect
to the mapping granularity in FTL, F2FS allocates each section of the active
logs from different zones as much as possible, since FTL can write the data in
the active logs into one allocation unit according to its mapping granularity.
Cleaning process
----------------
F2FS does cleaning both on demand and in the background. On-demand cleaning is
triggered when there are not enough free segments to serve VFS calls. Background
cleaner is operated by a kernel thread, and triggers the cleaning job when the
system is idle.
F2FS supports two victim selection policies: greedy and cost-benefit algorithms.
In the greedy algorithm, F2FS selects a victim segment having the smallest number
of valid blocks. In the cost-benefit algorithm, F2FS selects a victim segment
according to the segment age and the number of valid blocks in order to address
log block thrashing problem in the greedy algorithm. F2FS adopts the greedy
algorithm for on-demand cleaner, while background cleaner adopts cost-benefit
algorithm.
In order to identify whether the data in the victim segment are valid or not,
F2FS manages a bitmap. Each bit represents the validity of a block, and the
bitmap is composed of a bit stream covering whole blocks in main area.
Write-hint Policy
-----------------
1) whint_mode=off. F2FS only passes down WRITE_LIFE_NOT_SET.
2) whint_mode=user-based. F2FS tries to pass down hints given by
users.
===================== ======================== ===================
User F2FS Block
===================== ======================== ===================
N/A META WRITE_LIFE_NOT_SET
N/A HOT_NODE "
N/A WARM_NODE "
N/A COLD_NODE "
ioctl(COLD) COLD_DATA WRITE_LIFE_EXTREME
extension list " "
-- buffered io
WRITE_LIFE_EXTREME COLD_DATA WRITE_LIFE_EXTREME
WRITE_LIFE_SHORT HOT_DATA WRITE_LIFE_SHORT
WRITE_LIFE_NOT_SET WARM_DATA WRITE_LIFE_NOT_SET
WRITE_LIFE_NONE " "
WRITE_LIFE_MEDIUM " "
WRITE_LIFE_LONG " "
-- direct io
WRITE_LIFE_EXTREME COLD_DATA WRITE_LIFE_EXTREME
WRITE_LIFE_SHORT HOT_DATA WRITE_LIFE_SHORT
WRITE_LIFE_NOT_SET WARM_DATA WRITE_LIFE_NOT_SET
WRITE_LIFE_NONE " WRITE_LIFE_NONE
WRITE_LIFE_MEDIUM " WRITE_LIFE_MEDIUM
WRITE_LIFE_LONG " WRITE_LIFE_LONG
===================== ======================== ===================
3) whint_mode=fs-based. F2FS passes down hints with its policy.
===================== ======================== ===================
User F2FS Block
===================== ======================== ===================
N/A META WRITE_LIFE_MEDIUM;
N/A HOT_NODE WRITE_LIFE_NOT_SET
N/A WARM_NODE "
N/A COLD_NODE WRITE_LIFE_NONE
ioctl(COLD) COLD_DATA WRITE_LIFE_EXTREME
extension list " "
-- buffered io
WRITE_LIFE_EXTREME COLD_DATA WRITE_LIFE_EXTREME
WRITE_LIFE_SHORT HOT_DATA WRITE_LIFE_SHORT
WRITE_LIFE_NOT_SET WARM_DATA WRITE_LIFE_LONG
WRITE_LIFE_NONE " "
WRITE_LIFE_MEDIUM " "
WRITE_LIFE_LONG " "
-- direct io
WRITE_LIFE_EXTREME COLD_DATA WRITE_LIFE_EXTREME
WRITE_LIFE_SHORT HOT_DATA WRITE_LIFE_SHORT
WRITE_LIFE_NOT_SET WARM_DATA WRITE_LIFE_NOT_SET
WRITE_LIFE_NONE " WRITE_LIFE_NONE
WRITE_LIFE_MEDIUM " WRITE_LIFE_MEDIUM
WRITE_LIFE_LONG " WRITE_LIFE_LONG
===================== ======================== ===================
Fallocate(2) Policy
-------------------
The default policy follows the below POSIX rule.
Allocating disk space
The default operation (i.e., mode is zero) of fallocate() allocates
the disk space within the range specified by offset and len. The
file size (as reported by stat(2)) will be changed if offset+len is
greater than the file size. Any subregion within the range specified
by offset and len that did not contain data before the call will be
initialized to zero. This default behavior closely resembles the
behavior of the posix_fallocate(3) library function, and is intended
as a method of optimally implementing that function.
However, once F2FS receives ioctl(fd, F2FS_IOC_SET_PIN_FILE) in prior to
fallocate(fd, DEFAULT_MODE), it allocates on-disk block addressess having
zero or random data, which is useful to the below scenario where:
1. create(fd)
2. ioctl(fd, F2FS_IOC_SET_PIN_FILE)
3. fallocate(fd, 0, 0, size)
4. address = fibmap(fd, offset)
5. open(blkdev)
6. write(blkdev, address)
f2fs: support data compression This patch tries to support compression in f2fs. - New term named cluster is defined as basic unit of compression, file can be divided into multiple clusters logically. One cluster includes 4 << n (n >= 0) logical pages, compression size is also cluster size, each of cluster can be compressed or not. - In cluster metadata layout, one special flag is used to indicate cluster is compressed one or normal one, for compressed cluster, following metadata maps cluster to [1, 4 << n - 1] physical blocks, in where f2fs stores data including compress header and compressed data. - In order to eliminate write amplification during overwrite, F2FS only support compression on write-once file, data can be compressed only when all logical blocks in file are valid and cluster compress ratio is lower than specified threshold. - To enable compression on regular inode, there are three ways: * chattr +c file * chattr +c dir; touch dir/file * mount w/ -o compress_extension=ext; touch file.ext Compress metadata layout: [Dnode Structure] +-----------------------------------------------+ | cluster 1 | cluster 2 | ......... | cluster N | +-----------------------------------------------+ . . . . . . . . . Compressed Cluster . . Normal Cluster . +----------+---------+---------+---------+ +---------+---------+---------+---------+ |compr flag| block 1 | block 2 | block 3 | | block 1 | block 2 | block 3 | block 4 | +----------+---------+---------+---------+ +---------+---------+---------+---------+ . . . . . . +-------------+-------------+----------+----------------------------+ | data length | data chksum | reserved | compressed data | +-------------+-------------+----------+----------------------------+ Changelog: 20190326: - fix error handling of read_end_io(). - remove unneeded comments in f2fs_encrypt_one_page(). 20190327: - fix wrong use of f2fs_cluster_is_full() in f2fs_mpage_readpages(). - don't jump into loop directly to avoid uninitialized variables. - add TODO tag in error path of f2fs_write_cache_pages(). 20190328: - fix wrong merge condition in f2fs_read_multi_pages(). - check compressed file in f2fs_post_read_required(). 20190401 - allow overwrite on non-compressed cluster. - check cluster meta before writing compressed data. 20190402 - don't preallocate blocks for compressed file. - add lz4 compress algorithm - process multiple post read works in one workqueue Now f2fs supports processing post read work in multiple workqueue, it shows low performance due to schedule overhead of multiple workqueue executing orderly. 20190921 - compress: support buffered overwrite C: compress cluster flag V: valid block address N: NEW_ADDR One cluster contain 4 blocks before overwrite after overwrite - VVVV -> CVNN - CVNN -> VVVV - CVNN -> CVNN - CVNN -> CVVV - CVVV -> CVNN - CVVV -> CVVV 20191029 - add kconfig F2FS_FS_COMPRESSION to isolate compression related codes, add kconfig F2FS_FS_{LZO,LZ4} to cover backend algorithm. note that: will remove lzo backend if Jaegeuk agreed that too. - update codes according to Eric's comments. 20191101 - apply fixes from Jaegeuk 20191113 - apply fixes from Jaegeuk - split workqueue for fsverity 20191216 - apply fixes from Jaegeuk 20200117 - fix to avoid NULL pointer dereference [Jaegeuk Kim] - add tracepoint for f2fs_{,de}compress_pages() - fix many bugs and add some compression stats - fix overwrite/mmap bugs - address 32bit build error, reported by Geert. - bug fixes when handling errors and i_compressed_blocks Reported-by: <noreply@ellerman.id.au> Signed-off-by: Chao Yu <yuchao0@huawei.com> Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>
2019-11-01 13:07:14 +03:00
Compression implementation
--------------------------
- New term named cluster is defined as basic unit of compression, file can
be divided into multiple clusters logically. One cluster includes 4 << n
(n >= 0) logical pages, compression size is also cluster size, each of
cluster can be compressed or not.
f2fs: support data compression This patch tries to support compression in f2fs. - New term named cluster is defined as basic unit of compression, file can be divided into multiple clusters logically. One cluster includes 4 << n (n >= 0) logical pages, compression size is also cluster size, each of cluster can be compressed or not. - In cluster metadata layout, one special flag is used to indicate cluster is compressed one or normal one, for compressed cluster, following metadata maps cluster to [1, 4 << n - 1] physical blocks, in where f2fs stores data including compress header and compressed data. - In order to eliminate write amplification during overwrite, F2FS only support compression on write-once file, data can be compressed only when all logical blocks in file are valid and cluster compress ratio is lower than specified threshold. - To enable compression on regular inode, there are three ways: * chattr +c file * chattr +c dir; touch dir/file * mount w/ -o compress_extension=ext; touch file.ext Compress metadata layout: [Dnode Structure] +-----------------------------------------------+ | cluster 1 | cluster 2 | ......... | cluster N | +-----------------------------------------------+ . . . . . . . . . Compressed Cluster . . Normal Cluster . +----------+---------+---------+---------+ +---------+---------+---------+---------+ |compr flag| block 1 | block 2 | block 3 | | block 1 | block 2 | block 3 | block 4 | +----------+---------+---------+---------+ +---------+---------+---------+---------+ . . . . . . +-------------+-------------+----------+----------------------------+ | data length | data chksum | reserved | compressed data | +-------------+-------------+----------+----------------------------+ Changelog: 20190326: - fix error handling of read_end_io(). - remove unneeded comments in f2fs_encrypt_one_page(). 20190327: - fix wrong use of f2fs_cluster_is_full() in f2fs_mpage_readpages(). - don't jump into loop directly to avoid uninitialized variables. - add TODO tag in error path of f2fs_write_cache_pages(). 20190328: - fix wrong merge condition in f2fs_read_multi_pages(). - check compressed file in f2fs_post_read_required(). 20190401 - allow overwrite on non-compressed cluster. - check cluster meta before writing compressed data. 20190402 - don't preallocate blocks for compressed file. - add lz4 compress algorithm - process multiple post read works in one workqueue Now f2fs supports processing post read work in multiple workqueue, it shows low performance due to schedule overhead of multiple workqueue executing orderly. 20190921 - compress: support buffered overwrite C: compress cluster flag V: valid block address N: NEW_ADDR One cluster contain 4 blocks before overwrite after overwrite - VVVV -> CVNN - CVNN -> VVVV - CVNN -> CVNN - CVNN -> CVVV - CVVV -> CVNN - CVVV -> CVVV 20191029 - add kconfig F2FS_FS_COMPRESSION to isolate compression related codes, add kconfig F2FS_FS_{LZO,LZ4} to cover backend algorithm. note that: will remove lzo backend if Jaegeuk agreed that too. - update codes according to Eric's comments. 20191101 - apply fixes from Jaegeuk 20191113 - apply fixes from Jaegeuk - split workqueue for fsverity 20191216 - apply fixes from Jaegeuk 20200117 - fix to avoid NULL pointer dereference [Jaegeuk Kim] - add tracepoint for f2fs_{,de}compress_pages() - fix many bugs and add some compression stats - fix overwrite/mmap bugs - address 32bit build error, reported by Geert. - bug fixes when handling errors and i_compressed_blocks Reported-by: <noreply@ellerman.id.au> Signed-off-by: Chao Yu <yuchao0@huawei.com> Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>
2019-11-01 13:07:14 +03:00
- In cluster metadata layout, one special block address is used to indicate
a cluster is a compressed one or normal one; for compressed cluster, following
metadata maps cluster to [1, 4 << n - 1] physical blocks, in where f2fs
stores data including compress header and compressed data.
f2fs: support data compression This patch tries to support compression in f2fs. - New term named cluster is defined as basic unit of compression, file can be divided into multiple clusters logically. One cluster includes 4 << n (n >= 0) logical pages, compression size is also cluster size, each of cluster can be compressed or not. - In cluster metadata layout, one special flag is used to indicate cluster is compressed one or normal one, for compressed cluster, following metadata maps cluster to [1, 4 << n - 1] physical blocks, in where f2fs stores data including compress header and compressed data. - In order to eliminate write amplification during overwrite, F2FS only support compression on write-once file, data can be compressed only when all logical blocks in file are valid and cluster compress ratio is lower than specified threshold. - To enable compression on regular inode, there are three ways: * chattr +c file * chattr +c dir; touch dir/file * mount w/ -o compress_extension=ext; touch file.ext Compress metadata layout: [Dnode Structure] +-----------------------------------------------+ | cluster 1 | cluster 2 | ......... | cluster N | +-----------------------------------------------+ . . . . . . . . . Compressed Cluster . . Normal Cluster . +----------+---------+---------+---------+ +---------+---------+---------+---------+ |compr flag| block 1 | block 2 | block 3 | | block 1 | block 2 | block 3 | block 4 | +----------+---------+---------+---------+ +---------+---------+---------+---------+ . . . . . . +-------------+-------------+----------+----------------------------+ | data length | data chksum | reserved | compressed data | +-------------+-------------+----------+----------------------------+ Changelog: 20190326: - fix error handling of read_end_io(). - remove unneeded comments in f2fs_encrypt_one_page(). 20190327: - fix wrong use of f2fs_cluster_is_full() in f2fs_mpage_readpages(). - don't jump into loop directly to avoid uninitialized variables. - add TODO tag in error path of f2fs_write_cache_pages(). 20190328: - fix wrong merge condition in f2fs_read_multi_pages(). - check compressed file in f2fs_post_read_required(). 20190401 - allow overwrite on non-compressed cluster. - check cluster meta before writing compressed data. 20190402 - don't preallocate blocks for compressed file. - add lz4 compress algorithm - process multiple post read works in one workqueue Now f2fs supports processing post read work in multiple workqueue, it shows low performance due to schedule overhead of multiple workqueue executing orderly. 20190921 - compress: support buffered overwrite C: compress cluster flag V: valid block address N: NEW_ADDR One cluster contain 4 blocks before overwrite after overwrite - VVVV -> CVNN - CVNN -> VVVV - CVNN -> CVNN - CVNN -> CVVV - CVVV -> CVNN - CVVV -> CVVV 20191029 - add kconfig F2FS_FS_COMPRESSION to isolate compression related codes, add kconfig F2FS_FS_{LZO,LZ4} to cover backend algorithm. note that: will remove lzo backend if Jaegeuk agreed that too. - update codes according to Eric's comments. 20191101 - apply fixes from Jaegeuk 20191113 - apply fixes from Jaegeuk - split workqueue for fsverity 20191216 - apply fixes from Jaegeuk 20200117 - fix to avoid NULL pointer dereference [Jaegeuk Kim] - add tracepoint for f2fs_{,de}compress_pages() - fix many bugs and add some compression stats - fix overwrite/mmap bugs - address 32bit build error, reported by Geert. - bug fixes when handling errors and i_compressed_blocks Reported-by: <noreply@ellerman.id.au> Signed-off-by: Chao Yu <yuchao0@huawei.com> Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>
2019-11-01 13:07:14 +03:00
- In order to eliminate write amplification during overwrite, F2FS only
support compression on write-once file, data can be compressed only when
all logical blocks in cluster contain valid data and compress ratio of
cluster data is lower than specified threshold.
f2fs: support data compression This patch tries to support compression in f2fs. - New term named cluster is defined as basic unit of compression, file can be divided into multiple clusters logically. One cluster includes 4 << n (n >= 0) logical pages, compression size is also cluster size, each of cluster can be compressed or not. - In cluster metadata layout, one special flag is used to indicate cluster is compressed one or normal one, for compressed cluster, following metadata maps cluster to [1, 4 << n - 1] physical blocks, in where f2fs stores data including compress header and compressed data. - In order to eliminate write amplification during overwrite, F2FS only support compression on write-once file, data can be compressed only when all logical blocks in file are valid and cluster compress ratio is lower than specified threshold. - To enable compression on regular inode, there are three ways: * chattr +c file * chattr +c dir; touch dir/file * mount w/ -o compress_extension=ext; touch file.ext Compress metadata layout: [Dnode Structure] +-----------------------------------------------+ | cluster 1 | cluster 2 | ......... | cluster N | +-----------------------------------------------+ . . . . . . . . . Compressed Cluster . . Normal Cluster . +----------+---------+---------+---------+ +---------+---------+---------+---------+ |compr flag| block 1 | block 2 | block 3 | | block 1 | block 2 | block 3 | block 4 | +----------+---------+---------+---------+ +---------+---------+---------+---------+ . . . . . . +-------------+-------------+----------+----------------------------+ | data length | data chksum | reserved | compressed data | +-------------+-------------+----------+----------------------------+ Changelog: 20190326: - fix error handling of read_end_io(). - remove unneeded comments in f2fs_encrypt_one_page(). 20190327: - fix wrong use of f2fs_cluster_is_full() in f2fs_mpage_readpages(). - don't jump into loop directly to avoid uninitialized variables. - add TODO tag in error path of f2fs_write_cache_pages(). 20190328: - fix wrong merge condition in f2fs_read_multi_pages(). - check compressed file in f2fs_post_read_required(). 20190401 - allow overwrite on non-compressed cluster. - check cluster meta before writing compressed data. 20190402 - don't preallocate blocks for compressed file. - add lz4 compress algorithm - process multiple post read works in one workqueue Now f2fs supports processing post read work in multiple workqueue, it shows low performance due to schedule overhead of multiple workqueue executing orderly. 20190921 - compress: support buffered overwrite C: compress cluster flag V: valid block address N: NEW_ADDR One cluster contain 4 blocks before overwrite after overwrite - VVVV -> CVNN - CVNN -> VVVV - CVNN -> CVNN - CVNN -> CVVV - CVVV -> CVNN - CVVV -> CVVV 20191029 - add kconfig F2FS_FS_COMPRESSION to isolate compression related codes, add kconfig F2FS_FS_{LZO,LZ4} to cover backend algorithm. note that: will remove lzo backend if Jaegeuk agreed that too. - update codes according to Eric's comments. 20191101 - apply fixes from Jaegeuk 20191113 - apply fixes from Jaegeuk - split workqueue for fsverity 20191216 - apply fixes from Jaegeuk 20200117 - fix to avoid NULL pointer dereference [Jaegeuk Kim] - add tracepoint for f2fs_{,de}compress_pages() - fix many bugs and add some compression stats - fix overwrite/mmap bugs - address 32bit build error, reported by Geert. - bug fixes when handling errors and i_compressed_blocks Reported-by: <noreply@ellerman.id.au> Signed-off-by: Chao Yu <yuchao0@huawei.com> Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>
2019-11-01 13:07:14 +03:00
- To enable compression on regular inode, there are three ways:
* chattr +c file
* chattr +c dir; touch dir/file
* mount w/ -o compress_extension=ext; touch file.ext
* mount w/ -o compress_extension=*; touch any_file
- At this point, compression feature doesn't expose compressed space to user
directly in order to guarantee potential data updates later to the space.
Instead, the main goal is to reduce data writes to flash disk as much as
possible, resulting in extending disk life time as well as relaxing IO
congestion. Alternatively, we've added ioctl interface to reclaim compressed
space and show it to user after putting the immutable bit.
Compress metadata layout::
[Dnode Structure]
+-----------------------------------------------+
| cluster 1 | cluster 2 | ......... | cluster N |
+-----------------------------------------------+
. . . .
. . . .
. Compressed Cluster . . Normal Cluster .
+----------+---------+---------+---------+ +---------+---------+---------+---------+
|compr flag| block 1 | block 2 | block 3 | | block 1 | block 2 | block 3 | block 4 |
+----------+---------+---------+---------+ +---------+---------+---------+---------+
. .
. .
. .
+-------------+-------------+----------+----------------------------+
| data length | data chksum | reserved | compressed data |
+-------------+-------------+----------+----------------------------+
f2fs: support zone capacity less than zone size NVMe Zoned Namespace devices can have zone-capacity less than zone-size. Zone-capacity indicates the maximum number of sectors that are usable in a zone beginning from the first sector of the zone. This makes the sectors sectors after the zone-capacity till zone-size to be unusable. This patch set tracks zone-size and zone-capacity in zoned devices and calculate the usable blocks per segment and usable segments per section. If zone-capacity is less than zone-size mark only those segments which start before zone-capacity as free segments. All segments at and beyond zone-capacity are treated as permanently used segments. In cases where zone-capacity does not align with segment size the last segment will start before zone-capacity and end beyond the zone-capacity of the zone. For such spanning segments only sectors within the zone-capacity are used. During writes and GC manage the usable segments in a section and usable blocks per segment. Segments which are beyond zone-capacity are never allocated, and do not need to be garbage collected, only the segments which are before zone-capacity needs to garbage collected. For spanning segments based on the number of usable blocks in that segment, write to blocks only up to zone-capacity. Zone-capacity is device specific and cannot be configured by the user. Since NVMe ZNS device zones are sequentially write only, a block device with conventional zones or any normal block device is needed along with the ZNS device for the metadata operations of F2fs. A typical nvme-cli output of a zoned device shows zone start and capacity and write pointer as below: SLBA: 0x0 WP: 0x0 Cap: 0x18800 State: EMPTY Type: SEQWRITE_REQ SLBA: 0x20000 WP: 0x20000 Cap: 0x18800 State: EMPTY Type: SEQWRITE_REQ SLBA: 0x40000 WP: 0x40000 Cap: 0x18800 State: EMPTY Type: SEQWRITE_REQ Here zone size is 64MB, capacity is 49MB, WP is at zone start as the zones are in EMPTY state. For each zone, only zone start + 49MB is usable area, any lba/sector after 49MB cannot be read or written to, the drive will fail any attempts to read/write. So, the second zone starts at 64MB and is usable till 113MB (64 + 49) and the range between 113 and 128MB is again unusable. The next zone starts at 128MB, and so on. Signed-off-by: Aravind Ramesh <aravind.ramesh@wdc.com> Signed-off-by: Damien Le Moal <damien.lemoal@wdc.com> Signed-off-by: Niklas Cassel <niklas.cassel@wdc.com> Reviewed-by: Chao Yu <yuchao0@huawei.com> Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>
2020-07-16 15:56:56 +03:00
Compression mode
--------------------------
f2fs supports "fs" and "user" compression modes with "compression_mode" mount option.
With this option, f2fs provides a choice to select the way how to compress the
compression enabled files (refer to "Compression implementation" section for how to
enable compression on a regular inode).
1) compress_mode=fs
This is the default option. f2fs does automatic compression in the writeback of the
compression enabled files.
2) compress_mode=user
This disables the automatic compression and gives the user discretion of choosing the
target file and the timing. The user can do manual compression/decompression on the
compression enabled files using F2FS_IOC_DECOMPRESS_FILE and F2FS_IOC_COMPRESS_FILE
ioctls like the below.
To decompress a file,
fd = open(filename, O_WRONLY, 0);
ret = ioctl(fd, F2FS_IOC_DECOMPRESS_FILE);
To compress a file,
fd = open(filename, O_WRONLY, 0);
ret = ioctl(fd, F2FS_IOC_COMPRESS_FILE);
f2fs: support zone capacity less than zone size NVMe Zoned Namespace devices can have zone-capacity less than zone-size. Zone-capacity indicates the maximum number of sectors that are usable in a zone beginning from the first sector of the zone. This makes the sectors sectors after the zone-capacity till zone-size to be unusable. This patch set tracks zone-size and zone-capacity in zoned devices and calculate the usable blocks per segment and usable segments per section. If zone-capacity is less than zone-size mark only those segments which start before zone-capacity as free segments. All segments at and beyond zone-capacity are treated as permanently used segments. In cases where zone-capacity does not align with segment size the last segment will start before zone-capacity and end beyond the zone-capacity of the zone. For such spanning segments only sectors within the zone-capacity are used. During writes and GC manage the usable segments in a section and usable blocks per segment. Segments which are beyond zone-capacity are never allocated, and do not need to be garbage collected, only the segments which are before zone-capacity needs to garbage collected. For spanning segments based on the number of usable blocks in that segment, write to blocks only up to zone-capacity. Zone-capacity is device specific and cannot be configured by the user. Since NVMe ZNS device zones are sequentially write only, a block device with conventional zones or any normal block device is needed along with the ZNS device for the metadata operations of F2fs. A typical nvme-cli output of a zoned device shows zone start and capacity and write pointer as below: SLBA: 0x0 WP: 0x0 Cap: 0x18800 State: EMPTY Type: SEQWRITE_REQ SLBA: 0x20000 WP: 0x20000 Cap: 0x18800 State: EMPTY Type: SEQWRITE_REQ SLBA: 0x40000 WP: 0x40000 Cap: 0x18800 State: EMPTY Type: SEQWRITE_REQ Here zone size is 64MB, capacity is 49MB, WP is at zone start as the zones are in EMPTY state. For each zone, only zone start + 49MB is usable area, any lba/sector after 49MB cannot be read or written to, the drive will fail any attempts to read/write. So, the second zone starts at 64MB and is usable till 113MB (64 + 49) and the range between 113 and 128MB is again unusable. The next zone starts at 128MB, and so on. Signed-off-by: Aravind Ramesh <aravind.ramesh@wdc.com> Signed-off-by: Damien Le Moal <damien.lemoal@wdc.com> Signed-off-by: Niklas Cassel <niklas.cassel@wdc.com> Reviewed-by: Chao Yu <yuchao0@huawei.com> Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>
2020-07-16 15:56:56 +03:00
NVMe Zoned Namespace devices
----------------------------
- ZNS defines a per-zone capacity which can be equal or less than the
zone-size. Zone-capacity is the number of usable blocks in the zone.
F2FS checks if zone-capacity is less than zone-size, if it is, then any
f2fs: support zone capacity less than zone size NVMe Zoned Namespace devices can have zone-capacity less than zone-size. Zone-capacity indicates the maximum number of sectors that are usable in a zone beginning from the first sector of the zone. This makes the sectors sectors after the zone-capacity till zone-size to be unusable. This patch set tracks zone-size and zone-capacity in zoned devices and calculate the usable blocks per segment and usable segments per section. If zone-capacity is less than zone-size mark only those segments which start before zone-capacity as free segments. All segments at and beyond zone-capacity are treated as permanently used segments. In cases where zone-capacity does not align with segment size the last segment will start before zone-capacity and end beyond the zone-capacity of the zone. For such spanning segments only sectors within the zone-capacity are used. During writes and GC manage the usable segments in a section and usable blocks per segment. Segments which are beyond zone-capacity are never allocated, and do not need to be garbage collected, only the segments which are before zone-capacity needs to garbage collected. For spanning segments based on the number of usable blocks in that segment, write to blocks only up to zone-capacity. Zone-capacity is device specific and cannot be configured by the user. Since NVMe ZNS device zones are sequentially write only, a block device with conventional zones or any normal block device is needed along with the ZNS device for the metadata operations of F2fs. A typical nvme-cli output of a zoned device shows zone start and capacity and write pointer as below: SLBA: 0x0 WP: 0x0 Cap: 0x18800 State: EMPTY Type: SEQWRITE_REQ SLBA: 0x20000 WP: 0x20000 Cap: 0x18800 State: EMPTY Type: SEQWRITE_REQ SLBA: 0x40000 WP: 0x40000 Cap: 0x18800 State: EMPTY Type: SEQWRITE_REQ Here zone size is 64MB, capacity is 49MB, WP is at zone start as the zones are in EMPTY state. For each zone, only zone start + 49MB is usable area, any lba/sector after 49MB cannot be read or written to, the drive will fail any attempts to read/write. So, the second zone starts at 64MB and is usable till 113MB (64 + 49) and the range between 113 and 128MB is again unusable. The next zone starts at 128MB, and so on. Signed-off-by: Aravind Ramesh <aravind.ramesh@wdc.com> Signed-off-by: Damien Le Moal <damien.lemoal@wdc.com> Signed-off-by: Niklas Cassel <niklas.cassel@wdc.com> Reviewed-by: Chao Yu <yuchao0@huawei.com> Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>
2020-07-16 15:56:56 +03:00
segment which starts after the zone-capacity is marked as not-free in
the free segment bitmap at initial mount time. These segments are marked
as permanently used so they are not allocated for writes and
consequently are not needed to be garbage collected. In case the
zone-capacity is not aligned to default segment size(2MB), then a segment
can start before the zone-capacity and span across zone-capacity boundary.
Such spanning segments are also considered as usable segments. All blocks
past the zone-capacity are considered unusable in these segments.