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Date: Mon, 21 Apr 2014 23:22:24 +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 02:34:13AM +0200, magnum wrote:
> Is there any reason for not using Posix memory mapping for wordlist 
> mode's memory buffer in Jumbo? It should make it simpler and a lot more 
> effective for concurrent sessions including but not limited to forked 
> ones. Or is there a problem I fail to see?

I think this is worth a try, while also keeping the present approach
(for Windows, and for systems where it's faster).

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.

Yes, concurrent sessions possibly using the same wordlist, and
especially --fork, are a reason to prefer mmap().

Alexander

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