On Tue, May 23, 2023 at 06:13:08PM -0400, corwin wrote: > On 5/23/23 6:06 PM, Eric Biggers wrote: > > On Tue, May 23, 2023 at 05:45:02PM -0400, J. corwin Coburn wrote: > > > MurmurHash3 is a fast, non-cryptographic, 128-bit hash. It was originally > > > written by Austin Appleby and placed in the public domain. This version has > > > been modified to produce the same result on both big endian and little > > > endian processors, making it suitable for use in portable persistent data. > > > > > > Signed-off-by: J. corwin Coburn <corwin@xxxxxxxxxx> > > > --- > > > drivers/md/dm-vdo/murmurhash3.c | 175 ++++++++++++++++++++++++++++++++ > > > drivers/md/dm-vdo/murmurhash3.h | 15 +++ > > > 2 files changed, 190 insertions(+) > > > create mode 100644 drivers/md/dm-vdo/murmurhash3.c > > > create mode 100644 drivers/md/dm-vdo/murmurhash3.h > > > > Do we really need yet another hash algorithm? > > > > xxHash is another very fast non-cryptographic hash algorithm that is already > > available in the kernel (lib/xxhash.c). > > > > - Eric > > The main reason why vdo uses Murmur3 and not xxHash is that vdo has been in > deployment since 2013, and, if I am reading correctly, xxHash did not have a > 128 bit variant until 2019. Why do you need a 128-bit non-cryptographic hash algorithm? What problem are you trying to solve? > > It would certainly be possible to switch vdo to xxHash, but it would be > problematic for existing users. > Well, this commit doesn't mention that the choice was forced for compatibility reasons. It sounds like the on-disk format (and presumably the UAPI, too?) for dm-vdo was already set in stone before it was ever sent out for review. That takes away some motivation to bother reviewing it, since many review comments will be met with "we won't change this"... - Eric -- dm-devel mailing list dm-devel@xxxxxxxxxx https://listman.redhat.com/mailman/listinfo/dm-devel
