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13 addressing the fundamental issues in LFS, which are snowball effect of wandering
41 implementation of a log-structured file system", ACM Trans. Computer Systems
46 In LFS, when a file data is updated and written to the end of log, its direct
58 Since LFS is based on out-of-place writes, it produces so many obsolete blocks
63 The process consists of three operations as follows.
65 2. It loads parent index structures of all the data in the victim identified by
72 amount of valid data to be moved, and move them quickly as well.
87 - Introduce Node Address Table (NAT) containing the locations of all the “node”
113 segments for data from the beginning of main area, while
114 for node from the end of main area.
119 active_logs=%u Support configuring the number of active logs. In the
123 does not aware of cold files such as media files.
129 space of inode block which is used to store inline
138 but f2fs still guarantees the write ordering of all the
188 gc_idle This parameter controls the selection of victim
194 reclaim_segments This parameter controls the number of prefree
195 segments to be reclaimed. If the number of prefree
196 segments is larger than the number of segments
200 By default, 5% over total # of segments.
202 max_small_discards This parameter controls the number of discard
208 trim_sections This parameter controls the number of sections
212 ipu_policy This parameter controls the policy of in-place
220 of the filesystem utilization, and used by
225 The number indicates the number of dirty pages
230 max_victim_search This parameter controls the number of trials to
237 number of files, it can reduce the file lookup
265 The mkfs.f2fs is for the use of formatting a partition as the f2fs filesystem,
268 The options consist of:
270 -a [0 or 1] : Split start location of each area for heap-based allocation.
274 -s [int] : Set the number of segments per section.
276 -z [int] : Set the number of sections per zone.
284 The fsck.f2fs is a tool to check the consistency of an f2fs-formatted
287 Note that, initial version of the tool does not fix any inconsistency.
289 The options consist of:
294 The dump.f2fs shows the information of specific inode and dumps SSA and SIT to
297 The dump.f2fs is used to debug on-disk data structures of the f2fs filesystem.
302 The options consist of:
320 F2FS divides the whole volume into a number of segments, each of which is fixed
321 to 2MB in size. A section is composed of consecutive segments, and a zone
322 consists of a set of sections. By default, section and zone sizes are set to one
326 consists of multiple segments as described below.
348 : It is located at the beginning of the partition, and there exist two copies
350 default parameters of f2fs.
354 inode lists, and summary entries of current active segments.
358 validity of all the blocks.
361 : It is composed of a block address table for all the node blocks stored in
365 : It contains summary entries which contains the owner information of all the
372 aligns the start block address of CP with the segment size. Also, it aligns the
373 start block address of Main area with the zone size by reserving some segments
384 CP area. In order to reduce the scanning time, F2FS uses only two copies of CP.
385 One of them always indicates the last valid data, which is called as shadow copy
408 traditional file structures, F2FS has three types of node: inode, direct node,
429 Note that, all the node blocks are mapped by NAT which means the location of
430 each node is translated by the NAT table. In the consideration of the wandering
431 tree problem, F2FS is able to cut off the propagation of node updates caused by
437 A directory entry occupies 11 bytes, which consists of the following attributes.
439 - hash hash value of the file name
441 - len the length of file name
444 A dentry block consists of 214 dentry slots and file names. Therein a bitmap is
470 a hash table with dedicated number of hash buckets as shown below. Note that
489 The number of blocks and buckets are determined by,
492 # of blocks in level #n = |
497 # of buckets in level #n = |
501 When F2FS finds a file name in a directory, at first a hash value of the file
503 dentry consisting of the file name and its inode number. If not found, F2FS
506 one bucket determined by the following equation, which shows O(log(# of files))
509 bucket number to scan in level #n = (hash value) % (# of buckets in level #n)
511 In the case of file creation, F2FS finds empty consecutive slots that cover the
512 file name. F2FS searches the empty slots in the hash tables of whole levels from
515 The following figure shows an example of two cases holding children.
525 Number of children = 6, Number of children = 3,
534 - Hot node contains direct node blocks of directories.
552 segment in a unit of section. F2FS expects that the section size would be the
553 same as the unit size of garbage collection in FTL. Furthermore, with respect
554 to the mapping granularity in FTL, F2FS allocates each section of the active
568 of valid blocks. In the cost-benefit algorithm, F2FS selects a victim segment
569 according to the segment age and the number of valid blocks in order to address
575 F2FS manages a bitmap. Each bit represents the validity of a block, and the
576 bitmap is composed of a bit stream covering whole blocks in main area.