(Cc'ed to linux-nilfs) On Fri, 25 Feb 2011 12:44:06 +0100, dexen deVries wrote: > On Friday 25 of February 2011 12:34:23 you wrote: > > I guess pinning files on the device is possible in some way. But > > Supporting FIBMAP, which internally means supporting iops->bmap vfs > > interface, sounds more delicate than FIEMAP because it is actually > > used to determine block location for raw-write access. The swapfile > > is an example of that. > > > > Strictly, FIEMAP has the same risk, but in practice, we are using it > > for more harmless purposes such like analyzing fragmentation or giving > > hint to read-ahead tools. > > As a sidenote, it seems hdparm has that `--fibmap' subcommand, but it actually > issues FIEMAP rather than FIBMAP ioctl. Thanks for the information. This actually worked on nilfs. > > If we can safely disable a swapfile on filesystem and we can widely > > share the basic premise that "writing to the block location acquired > > by FIBMAP is a very dangerous thing for log-structured filesystems or > > COW filesystems", we could add it. > > Perhaps it would be enough if FIBMAP implementation for NILFS checked if the > file has a `pin-it-down' attribute and only then returned anything other than > EINVAL. Sounds a good idea. > Regarding pinning a file to physical location on a device: if a file is part of > a snapshot, does its data or metadata ever get moved? Only GC routine can move data and metadata, and only nilfs_cleanerd triggers the routine. Nilfs freezes past data and namespace into snapshot without copying or moving blocks. nilfs_cleanerd (NILFS GC) moves blocks per segment not per file, so pinning files would be achieved by skipping reclamation of segments recording the pinned files. Thanks, Ryusuke Konishi > -- > dexen deVries > > [[[↓][→]]] > > > how does a C compiler get to be that big? what is all that code doing? > > iterators, string objects, and a full set of C macros that ensure > boundary conditions and improve interfaces. > > ron minnich, in response to Charles Forsyth > > http://9fans.net/archive/2011/02/90 -- To unsubscribe from this list: send the line "unsubscribe linux-nilfs" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
