On Mon, Feb 27, 2017 at 01:36:37PM -0800, Eric Biggers wrote: > On Mon, Feb 27, 2017 at 01:28:28PM -0700, Andreas Dilger wrote: > > On Feb 17, 2017, at 4:33 PM, Eric Biggers <ebiggers3@xxxxxxxxx> wrote: > > > > > > From: Eric Biggers <ebiggers@xxxxxxxxxx> > > > > > > When using both encryption and SELinux (or another feature that requires > > > an xattr per file) on a filesystem with 256-byte inodes, each file's > > > xattrs usually spill into an external xattr block. Currently, the > > > xattrs are inherited in the order ACL, security, then encryption. > > > Therefore, if spillage occurs, the encryption xattr will always end up > > > in the external block. This is not ideal because the encryption xattrs > > > contain a nonce, so they will always be unique and will prevent the > > > external xattr blocks from being deduplicated. > > > > > > To improve the situation, change the inheritance order to encryption, > > > ACL, then security. This gives the encryption xattr a better chance to > > > be stored in-inode, allowing the other xattr(s) to be deduplicated. > > > > > > Note that it may be better for userspace to format the filesystem with > > > 512-byte inodes in this case. However, it's not the default. > > > > > > Signed-off-by: Eric Biggers <ebiggers@xxxxxxxxxx> > > > > Reviewed-by: Andreas Dilger <adilger@xxxxxxxxx> > > > > Note that we've been using 512-byte xattrs for Lustre metadata servers > > for ages. We may want to consider enabling this by default when the > > filesystem features are set (e.g. crypto, inline data, etc). > > > > Having a general mechanism to bias xattrs to in-inode or external xattr > > storage would be nice also, but I don't know any way to do this beyond > > just having a list of xattr names and then prioritizing the ones that > > go into the in-inode space. > > > > I think it's a good idea to have mke2fs default to 512-byte inodes if > '-O inline_data' is specified. But with '-O encrypt' it may be more debatable > because there is no guarantee as to how many files userspace will actually > choose to encrypt. It could be almost the whole filesystem, or just a few > files, or even nothing at all. > > Regardless, I think adjusting the xattr inheritance order (as this patch does) > has advantages but no real disadvantages, so it might as well be done too. > > Eric Ted, this patch seems to have gotten missed; are you planning to apply it? Next cycle is fine too, but I'd like to get it in sometime. - Eric
