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Date: Mon, 14 Nov 2016 21:48:15 +0100
From: Solar Designer <>
Subject: Re: Loading high number of hashes on GPU

On Mon, Nov 14, 2016 at 06:18:25PM +0100, Patrick Proniewski wrote:
> Speaking about memory limit on GPU, is there any ?

It varies by format, specific GPU, etc.

> I've seen benches of hashcat on badass GPU using only 2GB of the 8GB VRAM available. I have not yet had the opportunity to use JtR on GPU and I wonder if the limit is the same.

Not necessarily the same.  A potentially relevant limit is what clinfo
lists as "Max memory allocation", but it varies across GPUs (can be a
different fraction of total GPU memory) and might not apply to a given
JtR format.  (And we could work on making it not apply where it
currently does.)  There may be other limitations in JtR formats as well,
not related to GPU/driver.  For example, the thresholds in bt.c (perfect
hash tables for fast hashes on GPU) suggest that it should work up to
200M hashes, and it tries to work beyond that but it might fail.

magnum - I also just noticed it does try to remove duplicates.  Hmm.
Anyway, that's not john-users material anymore (but is john-dev or
GitHub issue material).


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