[Python-Dev] mmap & munmap loop (Was: Compact ordered set

[Victor Stinner]

Sorry, I didn't get a coffee yet: more *often* in a venv.

Le mer. 27 févr. 2019 à 11:32, Victor Stinner <vstinner at redhat.com> a écrit :
>
> Any idea why Python calls mmap+munmap more even in a venv?
>
> Victor
>
> Le mer. 27 févr. 2019 à 10:00, INADA Naoki <songofacandy at gmail.com> a écrit :
> >
> > >
> > > > Ah, another interesting point, this huge slowdown happens only when bm_pickle.py
> > > > is executed through pyperformance.  When run it directly, slowdown is
> > > > not so large.
> > >
> > > pyperformance runs benchmarks in a virtual environment. I don't know
> > > if it has any impact on bm_pickle.
> > >
> > > Most pyperformance can be run outside a virtual env if required
> > > modules are installed on the system. (bm_pickle only requires the
> > > stdlib and perf.)
> > >
> >
> > Bingo!
> >
> > Without venv:
> >
> > unpickle: Mean +- std dev: 26.9 us +- 0.0 us
> > % time     seconds  usecs/call     calls    errors syscall
> > ------ ----------- ----------- --------- --------- ----------------
> >  28.78    0.000438           0      1440           read
> >  27.33    0.000416           1       440        25 stat
> >   9.72    0.000148           1       144           mmap
> > ...
> >   0.79    0.000012           1        11           munmap
> >
> > With venv:
> >
> > % time     seconds  usecs/call     calls    errors syscall
> > ------ ----------- ----------- --------- --------- ----------------
> >  57.12    0.099023           2     61471           munmap
> >  41.87    0.072580           1     61618           mmap
> >   0.23    0.000395           1       465        27 stat
> >
> > unpickle and unpickle_list creates massive same-sized objects, then all objects are
> > removed.  If all pools in the arena is freed, munmap is called.
> >
> > I think we should save some arenas to reuse.  On recent Linux,
> > we may be able to use MADV_FREE instead of munmap.
> >
>
>
> --
> Night gathers, and now my watch begins. It shall not end until my death.



-- 
Night gathers, and now my watch begins. It shall not end until my death.