Re: [Valgrind-users] some questions about valgrind massif

[yoma s. <sop...@gm...>]

hi Philippe:

> There is no free information in the massif outputs.
> massif only produces a sequence of snaphots, each snapshot gives
> the memory still allocated at the snapshot time.
>
> The memory allocated by main returns to 0, because all the memory
> allocated by main is freed. The graph effectively shows the absolute
> value of the memory allocated at the snapshot time.
> massif does not record the free stacktraces, it only records how
> much memory is allocated by a stacktrace (and this amount decreases
> when free is called).
>
> So, in summary:
>   * massif does *not* record 'free' stacktraces
>   * massif *only* record 'malloc' stacktraces
>   * massif maintains the memory allocated by a stacktrace
>     this amount is decreased when free is called.
>
> So, do not expect to find some details about free stacktraces, as these
> are not recorded.
Thanks for your kind explination ^^

>
> I think there is a bug in the massif logic to make a peak detailed
> snapshot at the moment of munmap: it should try to produce a peak
> snapshot when releasing the first page of munmap, not when releasing
> the last page.
I use vgdb and try to create snapshop with command, "monitor
detailed_snapshot xxx"
No matter I create snapshop before mmap or after mmap, I hightlight in
the below program, there is still no mmap information in the detail
snapshop file.
It seems the mmap is not recorded by massif even I manual trigger the snapshop.
If I miss anything or do any wrong experiment, please let me know.

appreciate your kind help,

        f();
        g();
         /****break Here*****/
        p = mmap (0, sb.st_size, PROT_READ, MAP_SHARED, fd, 0);
        if (p == MAP_FAILED) {
/****break Here*****/
                perror ("mmap");
                return 1;
        }