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Diffstat (limited to 'Documentation/filesystems/f2fs.txt')
| -rw-r--r-- | Documentation/filesystems/f2fs.txt | 52 |
1 files changed, 52 insertions, 0 deletions
diff --git a/Documentation/filesystems/f2fs.txt b/Documentation/filesystems/f2fs.txt index 3135b80df6da..41b5aa94b30f 100644 --- a/Documentation/filesystems/f2fs.txt +++ b/Documentation/filesystems/f2fs.txt @@ -235,6 +235,17 @@ checkpoint=%s[:%u[%]] Set to "disable" to turn off checkpointing. Set to "en 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. +compress_algorithm=%s Control compress algorithm, currently f2fs supports "lzo" + and "lz4" algorithm. +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. ================================================================================ DEBUGFS ENTRIES @@ -840,3 +851,44 @@ zero or random data, which is useful to the below scenario where: 4. address = fibmap(fd, offset) 5. open(blkdev) 6. write(blkdev, address) + +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. + +- In cluster metadata layout, one special block address 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 | + +-------------+-------------+----------+----------------------------+ |