[Bug malloc/14581] memalign allocations are often not reused after free

["nsz at gcc dot gnu.org" <sourceware-bugzilla@sourceware.org>]

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

Szabolcs Nagy <nsz at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |nsz at gcc dot gnu.org

--- Comment #20 from Szabolcs Nagy <nsz at gcc dot gnu.org> ---
i think i ran into this or a similar issue, but the proposed patch "[v4,1/1]
memalign: Support scanning for aligned chunks." does not seem to help.

example: 100 iterations where each iteration leaks 16+64 bytes, everything else
is freed, but every iteration seems to increase the heap by 3231744 bytes at
least. with GLIBC_TUNABLES=glibc.malloc.mmap_threshold=600000 there is no issue
(large allocations turn into mmap/munmap pairs).

#include <stdlib.h>
#include <string.h>
static void *volatile q;
static void use(void *p){ q = p; }
int main(int argc, char *argv[])
{
        void *p1;
        void *p2;
        void *p3;
        for (int i=0; i < 100; i++) {
                p1 = aligned_alloc(512, 1176064);
                memset(p1, 0, 1176064);
                p2 = malloc(16);
                p3 = malloc(64);
                use(p1);
                use(p2);
                use(p3);
                free(p1);
                p1 = aligned_alloc(256, 646656);
                p2 = aligned_alloc(1024, 3232768);
                memset(p2, 0, 3232768);
                p3 = malloc(128);
                use(p1);
                use(p2);
                use(p3);
                free(p2);
                free(p3);
                free(p1);
        }
}

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