Bug 640286

Created attachment 451664 [details]
libc_leak.c

[This is continuation from bug #598498, but I can't seem to be able to reopen that bug]

Description of problem:
I found 3 problems with the new per-thread allocator in glibc (--enable-experimental-malloc):
 - Total memory usage much higher than memory allocated (should be ~88MB, but is >400MB)
 - When threads are joined, the per-thread heaps are not freed
 - malloc_stats() doesn't seem to be aware of those heaps, it only reports ~7MB allocated

Version-Release number of selected component (if applicable):
RHEL 6 beta 2, glibc-2.12-1.4.el6.x86_64

How reproducible:
Always

Steps to Reproduce:
1. Downloade attached libc_leak.c
2. gcc libc_leak.c -pthread 
3. (ulimit -v 512000 -d 512000; ./a.out)
  
Actual results:
malloc failed: Cannot allocate memory
Arena 0:
system bytes     =     135168
in use bytes     =       2304
malloc failed: Cannot allocate memory
Arena 0:
system bytes     =     135168
in use bytes     =       2304
Arena 1:
system bytes     =    1183744
in use bytes     =    1050816
Arena 2:
system bytes     =    1183744
in use bytes     =    1050816
Arena 3:
system bytes     =    1183744
in use bytes     =    1050816
Arena 4:
system bytes     =    1183744
in use bytes     =    1050816
Arena 5:
system bytes     =    1183744
in use bytes     =    1050816
Arena 6:
system bytes     =    1183744
in use bytes     =    1050816
Total (incl. mmap):
system bytes     =    7237632
Arena 1:
system bytes     =    1183744
in use bytes     =    1050816
in use bytes     =    6307200
max mmap regions =          0
max mmap bytes   =          0
Arena 2:
system bytes     =    1183744
in use bytes     =    1050816
Arena 3:
system bytes     =    1183744
in use bytes     =    1050816
Arena 4:
system bytes     =    1183744
in use bytes     =    1050816
Arena 5:
system bytes     =    1183744
in use bytes     =    1050816
Arena 6:
system bytes     =    1183744
in use bytes     =    1050816
Total (incl. mmap):
system bytes     =    7237632
in use bytes     =    6307200
max mmap regions =          0
max mmap bytes   =          0
/proc/self/status at exit

VmPeak:	  481288 kB
VmSize:	  430076 kB
VmLck:	       0 kB
VmHWM:	     740 kB
VmRSS:	     704 kB
VmData:	  424148 kB
VmStk:	      84 kB
VmExe:	       4 kB
VmLib:	    1704 kB
VmPTE:	      80 kB
VmSwap:	       0 kB


Expected results:
/proc/self/status at exit

VmPeak:   245696 kB
VmSize:   169916 kB
VmLck:         0 kB
VmHWM:       536 kB
VmRSS:       512 kB
VmData:   164060 kB
VmStk:       136 kB
VmExe:         4 kB
VmLib:      1588 kB
VmPTE:        68 kB
VmSwap:        0 kB


Additional info:
I originally reported this issue as #598498, but there doesn't seem to be a way to reopen that bug (not from my login at least), so I opened this new bug.

I've written a testcase to show the memory usage problems I see with clamd.

The testcase works like this:
 - starts NTHR threads
 - allocates 1MB in each
 - waits till all NTHR have allocated
 - frees everything.
 - at program exit Vm* is printed from /proc/self/status

This shouldn't use more than NTHR*(1MB + stacksize) memory.
With 8 threads, 8*(1MB + 10MB) = 88MB, so an ulimit of 512MB should be plenty, yet it is exceeded!

There are 3 issues here:
 - excessive memory usage (due to per-thread heaps?)
 - the per thread heaps are not freed when threads are joined
 - malloc_stats() doesn't seem to be aware of the per thread heaps: it says that only ~7MB was allocated, yet VmSize is >400MB 
 
The expected results are from a 2.11.2 eglibc, which was not built with --enable-experimental-malloc, and the actual results are from RHEL6's glibc which was built with --enable-experimental-malloc.

Without ulimit the testcase runs and prints VmSize: 561148 kB, so that is ~67MB/thread, which is way more than I requested with malloc. 

I wouldn't mind if glibc caches the anon mmaps per thread (as it does with the global heap already anyway), but it allocates way more than requested.