On Tue, Feb 12, 2013 at 04:00:54PM -0500, J. Bruce Fields wrote: > On Tue, Feb 12, 2013 at 09:56:41PM +0100, Bernd Schubert wrote: > > On 02/12/2013 09:28 PM, J. Bruce Fields wrote: > > > 06effdbb49af5f6c "nfsd: vfs_llseek() with 32 or 64 bit offsets (hashes)" > > > and previous patches solved problems with hash collisions in large > > > directories by using 64- instead of 32- bit directory hashes in some > > > cases. But it caused problems for users who assume directory offsets > > > are "small". Two cases we've run across: > > > > > > - older NFS clients: 64-bit cookies cause applications on many > > > older clients to fail. > > > - gluster: gluster assumed that it could take the top bits of > > > the offset for its own use. > > > > > > In both cases we could argue we're in the right: the nfs protocol > > > defines cookies to be 64 bits, so clients should be prepared to handle > > > them (remapping to smaller integers if necessary to placate applications > > > using older system interfaces). And gluster was incorrect to assume > > > that the "offset" was really an "offset" as opposed to just an opaque > > > value. > > > > > > But in practice things that worked fine for a long time break on a > > > kernel upgrade. > > > > > > So at a minimum I think we owe people a workaround, and turning off > > > dir_index may not be practical for everyone. > > > > > > A "no_64bit_cookies" export option would provide a workaround for NFS > > > servers with older NFS clients, but not for applications like gluster. > > > > > > For that reason I'd rather have a way to turn this off on a given ext4 > > > filesystem. Is that practical? > > > > I think Ted needs to answer if he would accept another mount option. But > > before we are going this way, what is gluster doing if there are hash > > collions? > > They probably just haven't tested NFS with large enough directories. > The birthday paradox says you'd need about 2^16 entries to have a 50-50 > chance of hitting the problem. The Gluster NFS-server gets into an infinite loop: - https://bugzilla.redhat.com/show_bug.cgi?id=838784 The general advise (even before this Bug) is that XFS should be used, which is not affected with this problem (yet?). Cheers, Niels -- 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
