[LLVMdev] [RFC] [PATCH] Fix for sys::Process::GetMallocUsage() when using ptmalloc2 allocator in glibc

[Dan Liew]

Hi,

This is a proposed fix for bug 16847 [1]. It is essentially the patch
provided by Martin Nowack in the bug report but I have added a test
case and an ifdef macro around the modified code in
Process::GetMallocUsage()

The issue seems to be that the ptmalloc2 allocator used in glibc (in
my case 2.19) does not include mmap()'ed memory in mallinfo.uordblks
and so mallinfo.hblkhd needs to be added to the value that
Process::GetMallocUsage() will return.

Another easy way to see this issue (other than running the unit test)
is to build and run the attached "malloc-test.c" program on a system
that uses glibc. You will see that after malloc'ing 256MiB of memory
uordblks is still zero but hblkhd has increased.

This is an RFC because I'm not very happy with my use of...

#if defined(__GLIBC__)

This will work in the common case where glibc is being used with its
standard allocator. However it will completely fail in the case where
LLVM is being used as a library and a developer chooses to use a
different allocator. For example if tcmalloc [2] is used then the
calculation is wrong[3] because mallinfo.uordblks includes mmap()'ed
memory and so we would count mmap()'ed memory twice!

Thoughts?

[1] http://llvm.org/bugs/show_bug.cgi?id=16847
[2] http://goog-perftools.sourceforge.net/doc/tcmalloc.html
[3] https://github.com/klee/klee/pull/116

Thanks,
-- 
Dan Liew
PhD Student - Imperial College London
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