On Mon, Aug 16, 2010 at 03:34:12PM -0500, Anthony Liguori wrote: > On 08/16/2010 01:42 PM, Christoph Hellwig wrote: > >On Mon, Aug 16, 2010 at 09:43:09AM -0500, Anthony Liguori wrote: > >>>Also, ext4 is _very_ slow on O_SYNC writes (which is > >>>used in kvm with default cache). > >>Yeah, we probably need to switch to sync_file_range() to avoid the > >>journal commit on every write. > >> > >No, we don't. sync_file_range does not actually provide any data > >integrity. > > What do you mean by data integrity? sync_file_range only does pagecache-level writeout of the file data. It nevers calls into the actual filesystem, that means any block allocations (for filling holes / converting preallocated space in normal filesystems, or every write in COW-based filesstems like qcow2) never get flushes to disk, and even more importantly the disk write cache is never flushed. In short it's completely worthless for any real filesystem. -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
