On Wed, Jun 21, 2017 at 06:49:34PM -0700, Tahsin Erdogan wrote: > Ext4 now supports xattr values that are up to 64k in size (vfs limit). > Large xattr values are stored in external inodes each one holding a > single value. Once written the data blocks of these inodes are immutable. > > The real world use cases are expected to have a lot of value duplication > such as inherited acls etc. To reduce data duplication on disk, this patch > implements a deduplicator that allows sharing of xattr inodes. > > The deduplication is based on an in-memory hash lookup that is a best > effort sharing scheme. When a xattr inode is read from disk (i.e. > getxattr() call), its crc32c hash is added to a hash table. Before > creating a new xattr inode for a value being set, the hash table is > checked to see if an existing inode holds an identical value. If such an > inode is found, the ref count on that inode is incremented. On value > removal the ref count is decremented and if it reaches zero the inode is > deleted. > > The quota charging for such inodes is manually managed. Every reference > holder is charged the full size as if there was no sharing happening. > This is consistent with how xattr blocks are also charged. > > Signed-off-by: Tahsin Erdogan <tahsin@xxxxxxxxxx> Applied, thanks - Ted
