> This adds a document describing the mount options, proc entries, usage, and > design of Flash-Friendly File System, namely F2FS. > > Signed-off-by: Jaegeuk Kim <jaegeuk.kim <at> samsung.com> > --- > Documentation/filesystems/00-INDEX | 2 + > Documentation/filesystems/f2fs.txt | 314 > ++++++++++++++++++++++++++++++++++++ > 2 files changed, 316 insertions(+) > create mode 100644 Documentation/filesystems/f2fs.txt > > diff --git a/Documentation/filesystems/00-INDEX > b/Documentation/filesystems/00-INDEX > index 8c624a1..ce5fd46 100644 > --- a/Documentation/filesystems/00-INDEX > +++ b/Documentation/filesystems/00-INDEX > @@ -48,6 +48,8 @@ ext4.txt > - info, mount options and specifications for the Ext4 filesystem. > files.txt > - info on file management in the Linux kernel. > +f2fs.txt > + - info and mount options for the F2FS filesystem. > fuse.txt > - info on the Filesystem in User SpacE including mount options. > gfs2.txt > diff --git a/Documentation/filesystems/f2fs.txt > b/Documentation/filesystems/f2fs.txt > new file mode 100644 > index 0000000..cd3f846 > --- /dev/null > +++ b/Documentation/filesystems/f2fs.txt > @@ -0,0 +1,314 @@ > +================================================================================ > +WHAT IS Flash-Friendly File System (F2FS)? > +================================================================================ > + > +NAND flash memory-based storage devices, such as SSD, eMMC, and SD cards, > have > +been widely being used for ranging from mobile to server systems. Since they > are > +known to have different characteristics from the conventional rotational > disks, > +a file system, an upper layer to the storage device, should adapt to the > changes > +from the sketch. > + > +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 aka FTL, > +F2FS and its tools support various parameters not only for configuring > on-disk > +layout, but also for selecting allocation and cleaning algorithms.
This is pretty high-level, can you list the main F2FS design points that are optimized for NAND flash characteristics? First I thought it's log-structured so it automatically performs write wear-leveling. But F2FS is intended to be used on top of FTL? So the FTL already handles that, and also it appears F2FS is a hybrid between append-only and write in-place. Who will choose "various parameters" and select "allocation and cleaning algorithms" appropriate for the device? I wouldn't know what to parameter values to use. > +Index Structure > +--------------- > + > +The key data structure to manage the data locations is a "node". As similar > as > +traditional file structures, F2FS has three types of node: inode, direct > node, > +indirect node. F2FS assigns 4KB to an inode block where contains 929 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 * (929 + 2 * 1018 + 2 * 1018 * 1018 + 1018 * 1018 * 1018) := 3.94TB. > + > + Inode block (4KB) > + |- data (929) > + |- direct node (2) > + | `- data (1018) > + |- indirect node (2) > + | `- direct node (1018) > + | `- data (1018) > + `- triple indirect node (1) > + `- indirect node (1018) > + `- direct node (1018) > + `- data (1018) Earlier it says "one double indirect node pointer" but this diagram shows a "triple indirect node". The diagram itself suggests this should really be "double indirect node" because it points to 1 indirect node. Stefan -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
