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Date: Tue, 24 Jul 2012 15:33:19 +0200
From: Frank Dittrich <frank_dittrich@...mail.com>
To: john-users@...ts.openwall.com
Subject: Re: Confusing --mem-file-size=SIZE description
On 07/24/2012 01:42 PM, magnum wrote:
> On 2012-07-24 12:06, Frank Dittrich wrote:
>> The parameter --mem-file-size is mentioned in the usage output:
>> --mem-file-size=SIZE size threshold for wordlist preload (default 5 MB)
>>
>> It is also mentioned in doc/OPTIONS.
>> --mem-file-size=SIZE max. size of wordlist to preload into memory.
>>
>> The unit is not mentioned in the description, so I assume it is in bytes.
>> That means, to change the value from default 5 MB to 100 MB, I would
>> have to use --mem-file-size=100000000. Is that correct?
>> It would be nice to clarify this in doc/OPTIONS.
>
> Right.
>
>> The parameter --mem-file-size is also mentioned in doc/README.mpi.
>> Here, the special SIZE values 0, 1, 2 are mentioned.
>> Apparently, for MPI this parameter is mis-used for something completely
>> different. Especially the --mem-file-size=0 meaning in MPI mode is
>> unfortunate, since without MPI, this means: load the complete file into
>> memory. If you have enough memory, this is usually what you want.
>
> --mem=0 is not different - it's actually where the non-MPI behavior
> stems from. MPI or not, it is a short-cut for saying "buffer the file,
> no matter its size".
>
>> But for MPI that means, the sequence of password candidates tried will
>> not be optimal for wordlists with candidates sorted by popularity.
>
> I guess you base that statement on the incorrect assumption that MPI
> will buffer the first 1/n of the wordlist to the first node. This is not
> the case. Each node will buffer every n:th word.
Then I must have misunderstood this;
--mem-file-size=0 (force split loading, no leapfrog)
--mem-file-size=1 (force leapfrogging of words)
--mem-file-size=2 (force leapfrogging of rules)
Frank
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