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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”
114 segments for data from the beginning of main area, while
115 for node from the end of main area.
120 active_logs=%u Support configuring the number of active logs. In the
124 does not aware of cold files such as media files.
130 space of inode block which is used to store inline
139 but f2fs still guarantees the write ordering of all the
191 gc_idle This parameter controls the selection of victim
197 reclaim_segments This parameter controls the number of prefree
198 segments to be reclaimed. If the number of prefree
199 segments is larger than the number of segments
203 By default, 5% over total # of segments.
205 max_small_discards This parameter controls the number of discard
211 trim_sections This parameter controls the number of sections
215 ipu_policy This parameter controls the policy of in-place
223 of the filesystem utilization, and used by
228 The number indicates the number of dirty pages
233 max_victim_search This parameter controls the number of trials to
240 number of files, it can reduce the file lookup
268 The mkfs.f2fs is for the use of formatting a partition as the f2fs filesystem,
271 The options consist of:
273 -a [0 or 1] : Split start location of each area for heap-based allocation.
277 -s [int] : Set the number of segments per section.
279 -z [int] : Set the number of sections per zone.
287 The fsck.f2fs is a tool to check the consistency of an f2fs-formatted
290 Note that, initial version of the tool does not fix any inconsistency.
292 The options consist of:
297 The dump.f2fs shows the information of specific inode and dumps SSA and SIT to
300 The dump.f2fs is used to debug on-disk data structures of the f2fs filesystem.
305 The options consist of:
323 F2FS divides the whole volume into a number of segments, each of which is fixed
324 to 2MB in size. A section is composed of consecutive segments, and a zone
325 consists of a set of sections. By default, section and zone sizes are set to one
329 consists of multiple segments as described below.
351 : It is located at the beginning of the partition, and there exist two copies
353 default parameters of f2fs.
357 inode lists, and summary entries of current active segments.
361 validity of all the blocks.
364 : It is composed of a block address table for all the node blocks stored in
368 : It contains summary entries which contains the owner information of all the
375 aligns the start block address of CP with the segment size. Also, it aligns the
376 start block address of Main area with the zone size by reserving some segments
387 CP area. In order to reduce the scanning time, F2FS uses only two copies of CP.
388 One of them always indicates the last valid data, which is called as shadow copy
411 traditional file structures, F2FS has three types of node: inode, direct node,
432 Note that, all the node blocks are mapped by NAT which means the location of
433 each node is translated by the NAT table. In the consideration of the wandering
434 tree problem, F2FS is able to cut off the propagation of node updates caused by
440 A directory entry occupies 11 bytes, which consists of the following attributes.
442 - hash hash value of the file name
444 - len the length of file name
447 A dentry block consists of 214 dentry slots and file names. Therein a bitmap is
473 a hash table with dedicated number of hash buckets as shown below. Note that
492 The number of blocks and buckets are determined by,
495 # of blocks in level #n = |
500 # of buckets in level #n = |
504 When F2FS finds a file name in a directory, at first a hash value of the file
506 dentry consisting of the file name and its inode number. If not found, F2FS
509 one bucket determined by the following equation, which shows O(log(# of files))
512 bucket number to scan in level #n = (hash value) % (# of buckets in level #n)
514 In the case of file creation, F2FS finds empty consecutive slots that cover the
515 file name. F2FS searches the empty slots in the hash tables of whole levels from
518 The following figure shows an example of two cases holding children.
528 Number of children = 6, Number of children = 3,
537 - Hot node contains direct node blocks of directories.
555 segment in a unit of section. F2FS expects that the section size would be the
556 same as the unit size of garbage collection in FTL. Furthermore, with respect
557 to the mapping granularity in FTL, F2FS allocates each section of the active
571 of valid blocks. In the cost-benefit algorithm, F2FS selects a victim segment
572 according to the segment age and the number of valid blocks in order to address
578 F2FS manages a bitmap. Each bit represents the validity of a block, and the
579 bitmap is composed of a bit stream covering whole blocks in main area.