[PATCH] talloc_free_for_exit() and targeted write protection for talloc destructor

[Andrew Bartlett]

On Tue, 2016-11-29 at 08:53 +0100, Volker Lendecke wrote:
> On Tue, Nov 29, 2016 at 08:13:26PM +1300, Andrew Bartlett wrote:
> > 
> > On Tue, 2016-11-29 at 07:57 +0100, Volker Lendecke wrote:
> > > 
> > > On Tue, Nov 29, 2016 at 07:13:53AM +1300, Andrew Bartlett wrote:
> > > > 
> > > > 
> > > > In a hope of getting more attention and being more transparent,
> > > > here is
> > > > the talloc changes I included in my previous patch set.
> > > > 
> > > > As background, I want to make our LDAP server multi-process,
> > > > and
> > > > running a connect()/bind()/close() loop against the LDAP server
> > > > showed
> > > > a significant cost in talloc_free(ev) and talloc_autofree()
> > > > just
> > > > before
> > > > exit.
> > > 
> > > Question -- why don't you directly call exit() without the
> > > talloc_free(ev)? Or even _exit()? We should be able to live with
> > > crashed processes. What destructors are you missing?
> > 
> > I assumed there would at least be messaging database entries to un-
> > register.  _exit() seemed a little extreme, but I agree it is an
> > option, and of course exit() calls handlers registered with
> > atexit().  
> > 
> > Memory on the autofree context from that atexit() registered call
> > was
> > around half the overhead in our examination of the flame graphs. 
> 
> As long as you have smbd running, the messaging database entries will
> be cleaned up eventually. This is done in
> messaging_parent_dgm_cleanup_init & friends. In the parent doing the
> waitpid, you could also call messaging_cleanup() for the exited child
> to make this deterministic.

Thanks.  The standard process model code has good waitpid handlers
triggered from pipe disconnection, so we know the PID that went away
and what it was pretty reliably, I'll look into that as an alternate
option. 

Andrew Bartlett

-- 
Andrew Bartlett                       http://samba.org/~abartlet/
Authentication Developer, Samba Team  http://samba.org
Samba Developer, Catalyst IT          http://catalyst.net.nz/services/samba