To: phillips@innominate.de Subject: Re: [Ext2-devel] [rfc] Near-constant time directory index for Ext2 From: tytso@valinux.com Date: Wed, 21 Feb 2001 22:23:09 -0800 Daniel, Nice work! A couple of comments. If you make the beginning of each index block look like a an empty directory block (i.e, the first 8 blocks look like this): 32 bits: ino == 0 16 bits: rec_len == blocksize 16 bits: name_len = 0 ... then you will have full backwards compatibility, both for reading *and* writing. When reading, old kernels will simply ignore the index blocks, since it looks like it has an unpopulated directory entry. And if the kernel attempts to write into the directory, it will clear the BTREE_FL flag, in which case new kernels won't treat the directory as a tree anymore. (Running a smart e2fsck which knows about directory trees will be able to restore the tree structure). Is it worth it? Well, it means you lose an index entry from each directory block, thus reducing your fanout at each node of the tree by a worse case of 0.7% in the worst case (1k blocksize) and 0.2% if you're using 4k blocksizes. - Ted - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/