On (Wed) Mar 04 2009 [12:55:22], Daniel P. Berrange wrote: > On Mon, Mar 02, 2009 at 03:02:11PM +0530, Amit Shah wrote: > > > > Inspite of this if some feedback is needed for a non-extents-based file > > system, a run-time probe for the underlying file system can be made and > > we could default to a chunk-based allocation in that case. > > These results are quite impressive. It is better by orders of magnitude > for modern filesystems, and even on ext3 it has a slight edge. So I'm > inclined to say we should use posix_fallocate() by default at all > times. > > When we introduce the API for incremental feedback, we could do something > like call fallocate() in 1GB chunks so we can get some reasonable amount > of feedback while still keeping it very fast & well allocated on disk. Oh btw fallocate() seems to be an O(1) operation (at least on new file systems). Allocating a 5G file also gave me 0s:few microseconds delay. > And of course, just fallocate() the whole thing upfront if the user does > not provide a callback for requesting feedback. Amit -- Libvir-list mailing list Libvir-list@xxxxxxxxxx https://www.redhat.com/mailman/listinfo/libvir-list