Date: Sat, 14 Jul 2012 16:22:49 -0500 From: "jfoug" <jfoug@....net> To: <john-dev@...ts.openwall.com> Subject: RE: additional memory usage questions, and the db_password structures >From: Solar Designer [mailto:solar@...nwall.com] >Sent: Saturday, July 14, 2012 3:23 PM > >On Sat, Jul 14, 2012 at 02:34:19PM -0500, jfoug wrote: >> There are other areas of this which can have significant impacts on >> memory usage, for large count of input (i.e. reduce this overhead and >> improve scalability of JtR). >> >> These 2 are the next_hash pointer, and words pointer. >> > >We're already doing that. We also do it for the "login" pointer when >memory saving is enabled. See pw_size in ldr_load_pw_line(). > >... > >Yes, you seem to misunderstand what next_hash is. BTW, I edited the >comment on it in my patch introducing source(). > >What we can in fact do is reduce this to 1 pointer. We only use either >"next" or "next_hash" during cracking, not both at once. See the big >if/else in crk_password_loop(). We use both in the loader, but we can >try to come up with an algorithm that would not require that. At the >very least, one of these can be moved to the cold part of the structure. Sounds very good to me. I thought it was likely that during the crack loop, that both pointers would often not be needed, but now by this expmainatino, it sounds like one or the other will always not be needed. >> It may simply be a miss understanding on my part, I was pretty sure this was the case. Again, this is why I poked out the query a few weeks back, about doing a "john-developers 101" type information page. In several posts, you have mentioned "this is documented in such and such function declaration, in xyz.h" Yes, that is very true. Yet assuming that people writing to JtR will know all of this, and understand all of this information, and interplay, is really making a very sweeping set of assumptions. Jim.
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