On Fri, Jun 29, 2007 at 01:01:20PM -0700, Andrew Morton wrote: > > Guys, Mike and Sreenivasa at google are looking into implementing > fallocate() on ext2. Of course, any such implementation could and should > also be portable to ext3 and ext4 bitmapped files. What's the eventual goal of this work? Would it be for mainline use, or just something that would be used internally at Google? I'm not particularly ennthused about supporting two ways of doing fallocate(); one for ext4 and one for bitmap-based files in ext2/3/4. Is the benefit reallyworth it? What I would suggest, which would make much easier, is to make this be an incompatible extensions (which you as you point out is needed for security reasons anyway) and then steal the high bit from the block number field to indicate whether or not the block has been initialized or not. That way you don't end up having to seek to a potentially distant part of the disk to check out the bitmap. Also, you don't have to worry about how to recover if the "block initialized bitmap" inode gets smashed. The downside is that it reduces the maximum size of the filesystem supported by ext2 by a factor of two. But, there are at least two patch series floating about that promise to allow filesystem block sizes > than PAGE_SIZE which would allow you to recover the maximum size supported by the filesytem. Furthermore, I suspect (especially after listening to a very fasting Usenix Invited Talk by Jeffery Dean, a fellow from Google two weeks ago) that for many of Google's workloads, using a filesystem blocksize of 16K or 32K might not be a bad thing in any case. It would be a lot simpler.... - Ted - 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
