Hi,
Several years ago, I developed a Massif patch to let the client code
select which part of the code should be profiled with Massif. This is
particulary useful for scientific simulation codes which often have two
phases during the run :
1) initialisation's phase
2) main computational loop (heavy CPU load)
During phase 1, one allocates a lot of memory (reading meshes, creating
variables, ...) but the critical part is the main loop : bogus codes
slightly increase memory consumption but the increase due to one
iteration of the loop is tiny compared to the total amount of memory
allocated before the main loop. Since the memory is freed after the
loop, this is not a leak, but the code can run out of memory because
there are thousands and thousands of iterations.
To detect the problem with Massif, one has to let the code run many
iterations of the loop under valgrind ... and it's way too slow. The
patch I've made ease the detection of such a problem within just a few
iterations. It consists in two new command line options and three
client's requests :
--record-from-start=yes/no : this disables heap profiling until Massif
meets the client's request which tells it to start profiling the heap
(see below).
--disable-auto-snapshots=yes/no : this disables all the snapshots except
the ones that are explicitly asked in a client's request.
VALGRIND_START_MEM_RECORDING : this request tells Massif to start heap
profiling.
VALGRIND_STOP_MEM_RECORDING : this request tells Massif to stop heap
profiling.
VALGRIND_TAKE_DETAILED_SNAPSHOT : this request tells Massif to take a
detailed snapshot.
So using VALGRIND_START_MEM_RECORDING just before the main loop and
VALGRIND_TAKE_DETAILED_SNAPSHOT at the beginning of the loop, Massif can
report exactly what is going on during the main loop. As an example, I
made a regression test which simulates that problem (big initial
allocation and then tiny allocations in a loop).
Massif report without the patch:
MB
1.001^ :
| #::::::::::::::::::::::::::::::::::::::::::::::::::@:::::::::
| #:::::::::::: :::: :::: ::: ::::::::::: :::: ::: ::@
| #:::::::::::: :::: :::: ::: ::::::::::: :::: ::: ::@
| #:::::::::::: :::: :::: ::: ::::::::::: :::: ::: ::@
| #:::::::::::: :::: :::: ::: ::::::::::: :::: ::: ::@
| #:::::::::::: :::: :::: ::: ::::::::::: :::: ::: ::@
| #:::::::::::: :::: :::: ::: ::::::::::: :::: ::: ::@
| #:::::::::::: :::: :::: ::: ::::::::::: :::: ::: ::@
| #:::::::::::: :::: :::: ::: ::::::::::: :::: ::: ::@
| #:::::::::::: :::: :::: ::: ::::::::::: :::: ::: ::@
| #:::::::::::: :::: :::: ::: ::::::::::: :::: ::: ::@
| #:::::::::::: :::: :::: ::: ::::::::::: :::: ::: ::@
| #:::::::::::: :::: :::: ::: ::::::::::: :::: ::: ::@
| #:::::::::::: :::: :::: ::: ::::::::::: :::: ::: ::@
| #:::::::::::: :::: :::: ::: ::::::::::: :::: ::: ::@
| #:::::::::::: :::: :::: ::: ::::::::::: :::: ::: ::@
| #:::::::::::: :::: :::: ::: ::::::::::: :::: ::: ::@
| #:::::::::::: :::: :::: ::: ::::::::::: :::: ::: ::@
| #:::::::::::: :::: :::: ::: ::::::::::: :::: ::: ::@
0
+----------------------------------------------------------------------->MB
0 7.056
Massif report with the patch:
B
216^ @
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0
+----------------------------------------------------------------------->MB
0 4.550
I've developed the patch in a GIT branch that I've just rebased on the
master. I've updated the docs (NEWS, manual, ...) and created a
regression test for it in massif/tests. I think this feature could
interest other developers of scientific codes (even if, I think, DHAT
can now help with such issue), so if you (valgrind developers) think it
could be interesting to take a look at it, let me know : I can send you
the patch or do a pull request.
Thanks,
Loïc
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