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Message-ID: <20150915230530.GA6288@openwall.com>
Date: Wed, 16 Sep 2015 02:05:30 +0300
From: Solar Designer <solar@...nwall.com>
To: john-dev@...ts.openwall.com
Subject: Re: Judy array
On Wed, Sep 16, 2015 at 12:43:44AM +0200, magnum wrote:
> On 2015-09-15 09:57, magnum wrote:
> >On 2015-09-15 05:40, Solar Designer wrote:
> >>This saves 4 seconds, but only when -mem=999999999 is also used:
> >>
> >>-WordlistMemoryMap = Y
> >>+WordlistMemoryMap = N
> >
> >We could probably default to not mmap when that other buffer is used.
>
> I had a look, that's a no-go. When mmap was introduced the code was
> simplified a bit. I'm not going to make it worse again. We still need to
> re-write it from scratch (with "scratch" meaning the original non-Jumbo
> file).
>
> Also, I don't observe any gain from disabling mmap and only minimal gain
> from using --mem=0 when mmap is enabled (I stopped using -mem after mmap
> was implemented). I'm surprised by your results, especially given you
> were short on memory... or is it *because* of just that..?
No, I wasn't that short on memory. The machine has 16 GB, and after my
copy-on-write reducing fixes these test runs allocate at most 9 GB total
across the 8 processes. So there's still enough memory to have the
wordlist, etc. cached in RAM across the runs, etc.
Let me re-test...
First, I took the latest cracker.c. This got my prefetching disabled.
And, surprise, it's now 2 seconds slower (I still have SHR=0):
real 0m58.804s
user 4m26.433s
sys 0m18.934s
Maybe the prefetching is sometimes helping, after all, even though for
our current raw-md5 it's very limited (max_keys_per_crypt is only 12, so
those loops don't actually go to the hard-coded maximum of 64
outstanding prefetches).
Now, enabling mmap (still no prefetch, etc.):
real 1m0.847s
user 4m51.136s
sys 0m15.579s
In both cases, I also had -mem=0 on the command line.
Alexander
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