Date: Fri, 28 Aug 2015 01:41:08 +0200 From: magnum <john.magnum@...hmail.com> To: john-dev@...ts.openwall.com Subject: Re: -dev=... -fork=... wastes GPU memory On 2015-08-28 01:21, magnum wrote: > On 2015-08-25 11:46, magnum wrote: >> On 2015-08-25 07:26, Solar Designer wrote: >>> Running this command on super: >>> >>> ./john -form=md5crypt-opencl 6.md5crypt.pw -fork=3 -dev=0,1,5 >>> -mask='?l?l?l?l?l?l?l?l' >>> (...) >>> It looks like the two child processes that target other GPUs >>> nevertheless >>> consume some memory on this GPU card as well. Why is that, and can we >>> avoid it? >>> >>> I guess the same happens for AMD GPUs as well, but we don't have such >>> nice reporting for them. Recent nvidia-smi is very nice in this >>> respect. >> >> Interesting. Well, we do enumerate all GPUs and I guess we create some >> kind of context for all of them. Maybe we can drop the ones we wont use. >> I'll have a look at it. > > I had a look. We take care not to do *anyhing* OpenCL prior to forking. > Any such stuff is post-poned. Then right after forking, we enumerate > cards and pick one just as if each child was a single process. > > This made me think that the exact same thing will happen with just a > single process, but I just checked and apparently it isn't. Very > strange. I need to let this grow for a while. I found this now by pure coincidence: http://www.openwall.com/lists/john-dev/2013/07/02/11 (very long thread, several branches). Sounds a lot like a variant of the same problem. However, we did change a lot of stuff (eg. we're not initializing OpenCL at all for CPU formats, and never prior to forking). magnum
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