Re: [Valgrind-users] Are valgrind leak-check results valid if target allocates a block larger than 4G?

[WAROQUIERS P. <phi...@eu...>]

>With valgrind, the memory footprint is increased, and the allocation
>does eventually fail.  The footprint increase is caused, as I
>understand it, by valgrind keeping alive blocks that would normally be
>freed during realloc, so that it can check for accesses to those
>blocks.  In any case, the only relevant fact is that the footprint
>increases for the grow-by-realloc usage model, and can increase
>drastically.

Note that if the default value for the free list volume is used,
(what you call the "keeping alive blocks"), then this is not the
cause of huge memory footprint, as the default size of this free list
volume is rather small (20 Mb).

The memory footprint is increased due to various factors:
   1. the V-bit machinery of Valgrind/memcheck
   2. the additional overhead of the Valgrind malloc replacement
      compared to the libc malloc.
   3. the free list ("alive blocks") of memcheck
   4. Valgrind malloc replacement fragmentation when doing reallocation
      of big pieces of memory. (see bug 250101).
   5. other aspects (e.g. some other memory used internally by
Valgrind).
 
I think that 1 and 2 are somewhat proportional to the memory used by
a "native" execution.

3 is under user control, default value is rather small.

4 can however cause quadratic memory usage (see bug 250101).
In your case, I believe it was the factor 4 that caused the problem.

Waiting for a (enhanced) fix for 250101 (on which I am working),
realloc patterns should be avoided.


Philippe

____
 
This message and any files transmitted with it are legally privileged and intended for the sole use of the individual(s) or entity to whom they are addressed. If you are not the intended recipient, please notify the sender by reply and delete the message and any attachments from your system. Any unauthorised use or disclosure of the content of this message is strictly prohibited and may be unlawful.
 
Nothing in this e-mail message amounts to a contractual or legal commitment on the part of EUROCONTROL, unless it is confirmed by appropriately signed hard copy.
 
Any views expressed in this message are those of the sender.