Christoph Hellwig <hch@xxxxxxxxxxxxx> writes: > On Mon, Aug 08, 2011 at 05:05:20PM +0200, Miklos Szeredi wrote: >> > The loop code still calls them uncondtionally. This actually is a big >> > as write_begin and write_end require filesystems specific locking, >> > and might require code in the filesystem to e.g. update the ctime >> > properly. I'll let Miklos chime in if leaving them in was intentional, >> > and if it was a comment is probably justified. >> >> Loop checks for ->write_begin() and falls back to ->write if the former >> isn't defined. >> >> So I think the patch is fine. I tested loop over fuse, and it still >> works after the patch. > > It works, but it involves another data copy, which will slow down > various workloads that people at least historically cared about. AFAICS, normally there isn't an additional copy. If ->write_begin is defined the copy from the bio_vec to the filesystem page is done with transfer_none() in the loop driver. Otherwise the copy is done by ->write() itself on the kmapped bio. If there's a crypto transfer function then a temporary page will be used in the no write_begin case. But I don't think there the additional copy makes much difference or that anyone cares. Thanks, Miklos -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Fight unfair telecom internet charges in Canada: sign http://stopthemeter.ca/ Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>