As a heads up, I'm going to replace the win32 auto-tester's snn.lib with one
hand patched to use the new allocation
logic that Rainer produced some time ago (see attached email for the details).
If it goes well, I'll leave it in place and also roll it to the win64 tester
(which uses dmc as a 32bit app still for
compilation). If it goes badly, I'll roll back pretty quickly.
Later,
Brad
--- Begin Message ---
On 05.09.2012 00:39, Rainer Schuetze wrote:
On 05.09.2012 00:07, Andrei Alexandrescu wrote:
Interesting. Can we fix that?
If I read the dmc runtime library sources correctly (heap32/heap.cpp),
heap allocations work with a minimum chunk size of 64 kB but
unfortunately 4 bytes get added to the requested size before calling
VirtualAlloc. That actually blocks 128kB of virtual address space, but
only 64k+4 bytes are used.
So, I recommend just aligning to the next multiple of 64kB in
RTLHeap::MoreCore. Walter, can you rebuild snn.lib with an appropriate fix?
I patched snn.lib to that effect, i.e. replaced this code
if (Size < 0x10000)
Size = 0x10000;
else
Size += Size/5; // Allocate 20% more to eliminate fragmentation
with this:
Size = ((Size + 4 + Size/5 + 0xffff) & ~0xffff) - 4;
// 4 is added in call to sbrk
and ran this little test program:
import core.stdc.stdlib;
import core.stdc.stdio;
void main()
{
for(int i = 0; ; i++)
if(malloc(1024) is null)
{
printf("allocated %d MB\n", i/1024);
break;
}
}
Compiling with the original snn.lib and running under Win8/64bit, it
outputs 962 MB of allocated memory, 1954 MB if I set the
large-address-aware bit.
With the patch, it can allocate 1925 MB and 3906 MB, respectively.
It takes minutes to run this little program (no swapping involved, I
have 8GB of memory), slowing down to allocating about 5MB/s when
watching progress in the process explorer. That seems to suggest that
the heap function do not deal well with that amount of memory or at
least with this allocation pattern.
If you want to try it yourself, start your favorite hex editor, load
snn.lib, find
81 FE 00 00 01 00 73 07 BE 00 00 01 00 EB 0D 8B C6 BB 05 00 00 00 31 D2
F7 F3 01 C6 8D 56 04
and replace it with
89 f0 BB 05 00 00 00 31 D2 F7 F3 8D 84 30 03 00 01 00 25 00 00 FF FF 8D
70 FC 90 90 8D 56 04
Rainer
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