On Jan 3, 8:15 pm, Case Vanhorsen <cas...@gmail.com> wrote: > Hello, > > I discovered an interesting memory allocation behavior on Windows vs. > Linux. I was testing GMPY on 64-bit Windows when I stumbled into this. > GMPY replaces the native MPIR memory allocation routines with Python's > memory allocator. If I enable debugging in GMPY, I get a trace of all > the memory allocation calls. When I ran the following: > > python -mtimeit -n 1 -r 1 -s "import > gmpy;gmpy.mpz(3)**(2**27);gmpy.set_debug(1)" "a=a*a" 2>temp.txt > > and look at the output saved in temp.txt, I see that Linux generated > approximately 34 memory manager calls but Windows generates over > 100,000 calls. Most of the Windows allocations are for small (<8K) > chunks of memory while all the Linux requests are for more than 64K. > The performance between Linux and Windows is similar. Could it be that > Windows is not using alloca? > > I also think I found another memory allocation bug. If I run the above > multiplication repeatedly: > > python -mtimeit -s "import > gmpy;gmpy.mpz(3)**(2**27);gmpy.set_debug(1)" "a=a*a" 2>temp.txt > > it will eventually crash. In looking at the debug output, I see a > request to allocate 18446744073709498400 bytes of memory. > > I tested with both MPIR 1.2.2 and 1.3.0 and get similar behavior. I'm > using a custom version of GMPY with some fixes for size_t vs. long > issues that hasn't been committed but I will try to commit those > changes later today.
Hi Case That is _very_ useful information and may explain why Windows performance lgas that on Linux. A long time ago - in GMP days - I had to turn of the use of alloca as I kept getting crashes if I used it. I have not tried switching it on in MPIR but I will certainly look at this again. But _alloca is now deprecated on Windows and its replacement requires a 'free' procedure that alloca doesn't need. It may hence be quite difficult to take advantage of this in future. It all depends on how GMP/MPIR use alloca. Thanks for the debugging! Brian -- You received this message because you are subscribed to the Google Groups "mpir-devel" group. To post to this group, send email to mpir-de...@googlegroups.com. To unsubscribe from this group, send email to mpir-devel+unsubscr...@googlegroups.com. For more options, visit this group at http://groups.google.com/group/mpir-devel?hl=en.
