[Bug malloc/14581] New: glibc leaks memory and do not reuse after free (leading to unlimited RSS growth)

["dev at parallels dot com" <sourceware-bugzilla@sourceware.org>]

http://sourceware.org/bugzilla/show_bug.cgi?id=14581

             Bug #: 14581
           Summary: glibc leaks memory and do not reuse after free
                    (leading to unlimited RSS growth)
           Product: glibc
           Version: 2.15
            Status: NEW
          Severity: normal
          Priority: P2
         Component: malloc
        AssignedTo: unassigned@sourceware.org
        ReportedBy: dev@parallels.com
    Classification: Unclassified


If you run the program below you will find that it never really allocates more
then 100MB of RAM, while it's RSS grows >700MB (and higher if the internal loop
made longer):

--------------------------
Arena 0:
system bytes     =  759681024
in use bytes     =   75144000
Total (incl. mmap):
system bytes     =  759681024
in use bytes     =   75144000
max mmap regions =          0
max mmap bytes   =          0
---------------------------

The same is confirmed by kernel RSS if allocated memory is touched (below only
VSZ grows as memory is not touched).

Please note, that this program does a VERY simple thing it allocates/frees
objects of 2 fixed sizes only and number of objects is strictly limited, there
is no heap fragmentation if you print virtual addresses of allocated objects
and kernel VMAs, i.e. you will find a huge unused memory extents which are
never reused by glibc. So there is no place for excuses for such behavior like
fragmentation.

Tested on RHEL6.3 (glibc-2.12-1.80.el6_3.5) and on FC16
(glibc-2.14.90-24.fc16.9), FC17 (glibc-2.15).

--------------------------------------
#include <stdio.h>
#include <malloc.h>

#define LSIZE (65536+4096)
#define SSIZE 556
#define NL 500
#define NS 70000

int main(int argc, char **argv)
{
        void * bigalloc[NL];
        void * smallalloc[NS];
        int bptr = 0;
        int sptr = 0;
        int i;

        memset(bigalloc, 0, sizeof(bigalloc));
        memset(smallalloc, 0, sizeof(smallalloc));

        for (i = 0; i < (16*1024*1024*1024ULL)/65536; i++) {
                free(bigalloc[i % NL]);
                free(smallalloc[i % NS]);
                smallalloc[i % NS] = malloc(SSIZE);
                bigalloc[i % NL] = memalign(4096, LSIZE);
        }

        malloc_stats();
        system("ps axv|fgrep stressalloc");
}

--------------------------------------

Linked from https://bugzilla.redhat.com/show_bug.cgi?id=843478

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