On Thu, Dec 22, 2016 at 02:10:33PM +0100, Jason A. Donenfeld wrote: > On Thu, Dec 22, 2016 at 1:47 PM, Hannes Frederic Sowa > <hannes@xxxxxxxxxxxxxxxxxxx> wrote: > > following up on what appears to be a random subject: ;) > > > > IIRC, ext4 code by default still uses half_md4 for hashing of filenames > > in the htree. siphash seems to fit this use case pretty good. > > I saw this too. I'll try to address it in v8 of this series. This is a separate issue, and this series is getting a bit too complex. So I'd suggest pushing this off to a separate change. Changing the htree hash algorithm is an on-disk format change, and so we couldn't roll it out until e2fsprogs gets updated and rolled out pretty broadley. In fact George sent me patches to add siphash as a hash algorithm for htree a while back (for both the kernel and e2fsprogs), but I never got around to testing and applying them, mainly because while it's technically faster, I had other higher priority issues to work on --- and see previous comments regarding pixel peeping. Improving the hash algorithm by tens or even hundreds of nanoseconds isn't really going to matter since we only do a htree lookup on a file creation or cold cache lookup, and the SSD or HDD I/O times will dominate. And from the power perspective, saving microwatts of CPU power isn't going to matter if you're going to be spinning up the storage device.... - Ted -- To unsubscribe from this list: send the line "unsubscribe linux-crypto" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
