On Mon, Oct 25, 2010 at 9:34 PM, Li Zefan <l...@cn.fujitsu.com> wrote: > Chris Mason wrote: >> On Mon, Oct 25, 2010 at 03:11:22PM +0800, Li Zefan wrote: >>> Lzo is a much faster compression algorithm than gzib, so would allow >>> more users to enable transparent compression, and some users can >>> choose from compression ratio and compression speed. >> >> This is also much smaller than I expected, really nice. It looks like >> older kernels won't properly deal (nicely give EIO) with lzo compressed >> files? >> >> We can add compatbits to deal with that if it is the case. >> > > I forgot compatibility issue with older kernels.. > > Though I didn't test older kernels, I don't think they can deal with lzo > compressed files properly, at least not for inlined extents, in which > case I think btrfs will just show compressed data to the users. > > So yes, an incompat flag is needed.
I've been testing this set of patches on a 2.6.36 kernel with the latest btrfs-unstable patches, and I wanted to provide my positive feedback. The lzo compression patches worked as expected, and I did not encounter any stability problems in my testing (which mainly consisted of decompressing a root partition archive and doing some compiling chores in a chroot environment on that drive). I did some crude benchmarking on decompressing an archived root partition to an empty btrfs drive, and my results were similar to the results posted by Li Zefan in the original post. The lzo compression did not compress quite as well as zlib, but was much faster. I did some test mounting of a lzo-compressed partition with an older non-lzo-patched kernel, and as expected, the contents of the files were garbled. But I did not encounter kernel oops or other issues when trying to read the garbled files. I also wanted to confirm that my other zlib-compressed partitions did not encounter any issues when bouncing back and forth between a lzo-patched kernel and older kernels. As expected, I did not see any issues in the partitions that had only been mounted with zlib compression. You'll want an incompat flag as indicated in previous posts, but I look forward to seeing lzo compression in the future. -- To unsubscribe from this list: send the line "unsubscribe linux-btrfs" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
