[gambit-list] Dumping the heap

Dimitris Vyzovitis vyzo at hackzen.org
Fri Feb 2 08:42:21 EST 2018


pinning, if exposed, should be sufficient to implement it purely in
userland.

it would be immediately useful for my heap dumper -- i could use it to get
a
vector of stills from all processors with the
count-still-objects/get-still-objects
procedures before starting the walk and use that to ensure that all stills
(at the
beginning of the walk) are accounted for.

it would also be useful for implementing a parallel dispatch primitive that
utilizes
all cores maximally.  say you have a parallel algorithm that you want to
decompose
into per core tasks, that could be accomplished with on-all-processors (or
a similar
primitive based on pinning).  and it doesn't have to be a compute
algorithm, i/o could
benefit too.

-- vyzo

On Fri, Feb 2, 2018 at 3:32 PM, Marc Feeley <feeley at iro.umontreal.ca> wrote:

> The SMP scheduler support “pinning” threads to processors, so perhaps this
> is implementable.  However… why do you need this?  I don’t like exposing
> the processor concept or pinning, which are low-level concepts.
>
> Marc
>
>
>
> > On Feb 2, 2018, at 8:07 AM, Dimitris Vyzovitis <vyzo at hackzen.org> wrote:
> >
> > perhaps the "don't switch" semantics are too much.
> > a simpler general purpose primitive would be an `on-all-processors` that
> spawns
> > a thread on each processor to execute the thunk and completes when all
> thunks
> > have completed.
> >
> > that's likely implementable without any deep support from the runtime.
> >
> > -- vyzo
> >
> >
> > On Fri, Feb 2, 2018 at 3:00 PM, Dimitris Vyzovitis <vyzo at hackzen.org>
> wrote:
> > well, perhaps we can think about the right primitive for Scheme level
> operations.
> > the semantics could be something like "execute this thunk on all
> processors, and
> > don't do any switches until it has finished executing".
> >
> > -- vyzo
> >
> >
> > On Fri, Feb 2, 2018 at 2:57 PM, Marc Feeley <feeley at iro.umontreal.ca>
> wrote:
> > on_all_processors was designed for the lowest-level of the runtime
> system, I don’t think it is possible for the operation to be in Scheme
> (I’ll have to thinks about what the constraints are on the operation).
> >
> > Marc
> >
> >
> >
> > > On Feb 2, 2018, at 7:49 AM, Dimitris Vyzovitis <vyzo at hackzen.org>
> wrote:
> > >
> > > it would be nice to have a primitive to do this for Scheme procedures!
> > > Something like (on-all-processors thunk) would be awesome.
> > >
> > > -- vyzo
> > >
> > > On Fri, Feb 2, 2018 at 2:41 PM, Marc Feeley <feeley at iro.umontreal.ca>
> wrote:
> > > Yes each processor has its own still_objs list and to account for all
> still objects you must iterate over the processors.  In order to avoid
> modification of the still_objs lists while doing this the best approach is
> to use the barrier operation mechanism.  That way all processors (but one)
> will be idle while iterating (or you could have all processors cooperate).
> This is done with the “on_all_processors” function.  For an example, check
> out ___garbage_collect or ___fdset_resize in lib/setup.c .
> > >
> > > Marc
> > >
> > >
> > >
> > > > On Feb 2, 2018, at 6:23 AM, Dimitris Vyzovitis <vyzo at hackzen.org>
> wrote:
> > > >
> > > > Relevant code for accounting still objects:
> > > > https://gist.github.com/vyzo/ab4219382c0870779991d4c701921d2c
> > > >
> > > > The limitation is that the still_objs_ is per processor, and not
> vm-wide.
> > > > Does that mean we would have to crawl all processors in SMP?
> > > >
> > > > -- vyzo
> > > >
> > > >
> > > > On Thu, Feb 1, 2018 at 3:16 PM, Marc Feeley <feeley at iro.umontreal.ca>
> wrote:
> > > > > On Feb 1, 2018, at 8:06 AM, Dimitris Vyzovitis <vyzo at hackzen.org>
> wrote:
> > > > >
> > > > > thanks Guillaume!
> > > > >
> > > > > this is a great start for me -- i am helping fare debug a memory
> leak, and it's really hard to identify
> > > > > without dumping the heap to see what kind of object is leaking.
> > > >
> > > > For your information I discovered a few memory leaks with the
> networking functions.  They were due to “sockaddr” structures being
> converted to “still” Scheme objects with a reference count = 1, but the
> reference count was never decremented (with ___release_scmobj).  This has
> been fixed in the recent UDP commit.
> > > >
> > > > I believe that this kind of situation might exist in other places in
> the runtime system.  So it might be useful to debug this to have a function
> that returns a list of all the “still” Scheme objects that have a reference
> count != 0.  This should be easy to write… the GC maintains a list of the
> still objects in the C variable “still_objs”.
> > > >
> > > > So the idea would be to check at the end of a program if there are
> any still objects with non-zero ref counts.
> > > >
> > > > Marc
> > > >
> > > >
> > >
> > >
> >
> >
> >
>
>
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