On Tue, 2006-10-24 at 23:59 +1000, David Chinner wrote: > On Tue, Oct 24, 2006 at 12:14:33AM -0400, Jeff Garzik wrote: > > On Mon, Oct 23, 2006 at 06:31:40PM +0400, Alex Tomas wrote: > > > isn't that a kernel responsbility to find/allocate target blocks? > > > wouldn't it better to specify desirable target group and minimal > > > acceptable chunk of free blocks? > > > > The kernel doesn't have enough knowledge to know whether or not the > > defragger prefers one blkdev location over another. > > > > When you are trying to consolidate blocks, you must specify the > > destination as well as source blocks. > > > > Certainly, to prevent corruption and other nastiness, you must fail if > > the destination isn't available... > > That's the wrong way to look at it. if you want the userspace > process to specify a location, then you should preallocate it first > before doing anything else. There is no need to clutter a simple > data mover interface with all sorts of unnecessary error handling. You are implying the the 2-step interface, creating a new inode then swapping the contents, is the only way to implement this. > > Once you've separated the destination allocation from the data > mover, the mover is basically a splice copy from source to > destination, an fsync and then an atomic swap blocks/extents operation. > Most of this code is generic, and a per-fs swap-extents vector > could be easily provided for the one bit that is not.... The benefit of having such a simple data mover is negated by moving the complexity into the allocator. A single interface that would move a part of a file at a time has the advantage that a large file which is only fragmented in a few areas does not need to be completely moved. > The allocation interface, OTOH, is anything but simple and is really > a filesystem specific interface. Seems logical to me to separate > the two. So what then is the benefit of having a simple generic data mover if every file system needs to implement it's own interface to allocate a copy of the data? Shaggy -- David Kleikamp IBM Linux Technology Center - To unsubscribe from this list: send the line "unsubscribe linux-ext4" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
