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Message-ID: <20140421230110.GA30841@openwall.com>
Date: Tue, 22 Apr 2014 03:01:10 +0400
From: Solar Designer <solar@...nwall.com>
To: john-dev@...ts.openwall.com
Subject: Re: mmap(2) in wordlist.c
On Mon, Apr 21, 2014 at 11:56:03PM +0200, magnum wrote:
> On 2014-04-21 21:22, Solar Designer wrote:
> >I think this is worth a try, while also keeping the present approach
> >(for Windows, and for systems where it's faster).
>
> That clashes with a hidden agenda though: A total rewrite of wordlist.c
> starting with core 1.8 version, and re-implementing Jumbo features as
> cleanly and KISS as possible. Unless real-world performance in some
> situations end up a lot worse than today's, I'd like to drop the old
> buffering altogether, including the --mem-file-size option which ideally
> should not be needed.
Right. When I wrote "also keeping the present approach" I didn't mean
the present implementation of it in jumbo. And the approach may change
somewhat, too. I only meant that we need both a read() and a mmap()
version of the code.
> >I briefly experimented with read() vs. mmap() while developing popa3d,
> >in 1998 or 1999. At the time, read() turned out to be significantly
> >faster, on Linux 2.0.x and ext2fs, when the read buffer size is properly
> >tuned. I didn't try this experiment in JtR.
>
> What order of size was that at the time?
64 KB. I think somewhat larger worked OK too, but wasn't necessary.
popa3d still has it at 64 KB, I didn't bother re-tuning (and this might
still be nearly optimal anyway).
Alexander
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