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Subject: Re: [OMPI users] memalign usage in OpenMPI and it's consequences for TotalVIew
From: Samuel K. Gutierrez (samuel_at_[hidden])
Date: 2009-10-01 13:39:39


Hi,

I think Jeff has already addressed this problem.

https://svn.open-mpi.org/trac/ompi/changeset/21744

--
Samuel K. Gutierrez
Los Alamos National Laboratory
On Oct 1, 2009, at 11:25 AM, Peter Thompson wrote:
> We had a question from a user who had turned on memory debugging in  
> TotalView and experience a memory event error Invalid memory  
> alignment request.  Having a 1.3.3 build of OpenMPI handy, I tested  
> it and sure enough, saw the error.  I traced it down to, surprise, a  
> call to memalign.  I find there are a few places where memalign is  
> called, but the one I think I was dealing with was from malloc.c in  
> ompi/mca//io/romio/romio/adio/common in the following lines:
>
>
> #ifdef ROMIO_XFS
>    new = (void *) memalign(XFS_MEMALIGN, size);
> #else
>    new = (void *) malloc(size);
> #endif
>
> I searched, but couldn't find a value for XFS_MEMALIGN, so maybe it  
> was from opal_pt_malloc2_component.c instead, where the call is
>
>    p = memalign(1, 1024 * 1024);
>
> There are only 10 to 12 references to memalign in the code that I  
> can see, so it shouldn't be too hard to find.  What I can tell you  
> is that the value that TotalView saw for alignment, the first arg,  
> was 1, and the second, the size, was  0x100000, which is probably  
> right for 1024 squared.
>
> The man page for memalign says that the first argument is the  
> alignment that the allocated memory use, and it must be a power of  
> two.  The second is the length you want allocated.  One could argue  
> that 1 is a power of two, but it seems a bit specious to me, and  
> TotalView's memory debugger certainly objects to it. Can anyone tell  
> me what the intent here is, and whether the memalign alignment  
> argument is thought to be valid?  Or is this a bug (that might not  
> affect anyone other than TotalView memory debug users?)
>
> Thanks,
> Peter Thompson
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