Messages in this thread | | | Date | Sat, 1 Nov 2014 09:29:14 -0700 | Subject | Re: [GIT PULL] ext4 bug fixes for 3.18 | From | Linus Torvalds <> |
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On Sat, Nov 1, 2014 at 6:38 AM, Theodore Ts'o <tytso@mit.edu> wrote: > > I didn't think hash_64 was *that* slow, so it's not clear the above > would be faster, though. And if someone is using a > 16TB file system > on a 32-bit platform, I suspect they might be having other problems. :-)
Fair enough, hash_64() isn't *that* slow. But it _is_ 6 64-bit shifts and adds/subtracts, which on a 32-bit machine tends to be quite expensive. On some of them it's function calls etc.
And your point about >16TB filesystems is completely buggy. That was *my* point. Most people - even on 64-bit - do *not* have 16TB filesystems, and the high 32 bits are zero or contain very very little information (ie even on a multi-terabyte filesystem, it's one or two bits worth of information). So hash_32() is not only much more reasonable on a 32-bit machine, the end result is basically as good for 99.999% of all uses. Exactly *because* people don't have those big filesystems.
Linus
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