RFR(s-m): 8218988: Improve metaspace verifications

[Thomas Stüfe]

Thank you, Zhengyu!

I need a second reviewer, anyone?

..Thomas


On Mon, Feb 25, 2019 at 7:09 PM <zgu at redhat.com> wrote:

> Hi Thomas,
>
>
> > 1) It seems that it needs include "utilities/align.hpp" in
> > metaspaceCommon.hpp to make NON-PCH build happy.
>
>
> Good catch.
>
>
> >
> > 2) There are several instances this->xxxx() calls in
> > virtualSpaceNode.cpp, you want to clean them up? seems that you are
> > doing some cleanup in this patch anyway.
>
>
> I cleaned them up. Sometimes I leave them in for documentation purposes,
> but yes they clutter the code.
>
>
>
> Thanks for fixing.
>
> >
> > 3) chunkManager.hpp
> > I don't like this method:
> > const ChunkList* free_chunks(ChunkIndex index) const;
>
>
> Ok, I removed it and changed the callsite.
>
> Not really happy with it. Unfortunately there is no good alternative to
> const overloading, even though it is ugly... But I can live with this
> solution.
>
>
> Me too.
>
> 4) Also is_valid_chunksize(bool is_class, size_t size) can be a static
> or const method.
>
>
>
> It is a global function, not a class method. I can make it static but that
> would maybe mean something different that you intended?
>
> I must have misread this as a member function.
>
> Looks good to me.
>
> Thanks,
>
> -Zhengyu
>
> Thanks again,
>
> Thomas
>
>
>
>
> Thanks,
>
> -Zhengyu
>
> >
> > I see it is only used in debug code, make it debug only? or just cast
> > away const of *this* pointer at call site?
> >
> > Thanks,
> >
> > -Zhengyu
> >
> >
> >
> > On Fri, 2019-02-15 at 11:12 +0100, Thomas Stüfe wrote:
> > > Hi all,
> > >
> > > may I please have reviews for the following change:
> > >
> > > Bug: https://bugs.openjdk.java.net/browse/JDK-8218988
> > > cr:
> > > http://cr.openjdk.java.net/~stuefe/webrevs/8218988--improve-metaspa
> > > ce
> > > -verifications/webrev.00/webrev/
> > >
> > > In short, this reworks metaspace verifications.
> > >
> > > Thorough verifications were added for JDK-8198423, but turned out
> > > too
> > > slow
> > > in general, so were made switchable later (-XX:+VerifyMetaspace)
> > > with
> > > a
> > > switch which is usually off. However, it would be good to have
> > > these
> > > verifications at least sometimes, so this patch changes
> > > VerifyMetaspace
> > > from a boolean to an interval which causes verifications every n
> > > passes
> > > thru a verification callsite. The default is 500, which does not
> > > slow
> > > down
> > > metaspace-heavy tests like SelectionResolution noticably.
> > >
> > > This patch also contains a number of cleanups and simplifications.
> > > In
> > > particular:
> > >
> > > class ChunkManager:
> > >
> > > - removed sum_free_chunks(), sum_free_chunks_count(),
> > > locked_verify_free_chunks_total() and
> > > locked_verify_free_chunks_count().
> > > These functions were used to validate the counters in ChunkManager.
> > > But
> > > this way was inefficient, since we walk the lists twice. The
> > > counter
> > > validation is now done in ChunkManager::verify() and only requires
> > > one list
> > > walk. Also, less code.
> > > - Now we only have one verification function left,
> > > ChunkManager::verify().
> > > To distinguish between quick counter verify and deep costly verify,
> > > I
> > > gave
> > > it a "bool slow" argument.
> > > - all verifications are now #ifdef ASSERT. In fact, they were
> > > before
> > > too
> > > since we used assert() inside the verification functions.
> > > - expensive verifications are now done depending on
> > > VerifyMetaspaceInterval.
> > > - I removed expensive verifications from some hot paths (e.g.
> > > ChunkManager::chunk_freelist_allocate). Verifications are now done
> > > only
> > > when interesting things happen: chunk fuses or splits, or a
> > > Classloader
> > > died and releases its SpaceManager.
> > >
> > > minor stuff:
> > >
> > > - made getters for counters (free_chunks_total_words(),
> > > free_chunks_total_bytes(), free_chunks_count()) inline
> > > - removed locked_print_sum_free_chunks(), which was nowhere used.
> > > - constified versions of free_chunks() and humongous_dictionary()
> > >
> > > class VirtualSpaceNode:
> > >
> > > - removed container_count_slow() and verify_container_count() since
> > > it
> > > duplicates the verifications we do in VirtualSpaceNode::verify().
> > > - similar to ChunkManager, gave VirtualSpaceNode::verify a "bool
> > > slow"
> > > parameter to distinguish between quick and thorough verification.
> > > - modified
> > > VirtualSpaceNode::verify_free_chunks_are_ideally_merged()
> > > to
> > > print out a map of the node if it fails, before asserting.
> > >
> > > Miscellanous:
> > >
> > > - added some new internal counters to the statistic (see
> > > metaspaceCommon.hpp)
> > >
> > >
> > > Gtests: test_virtualSpaceNode.cpp
> > >
> > > - renamed ChunkManagerTest to ChunkManagerTestAccessor to make its
> > > (narrow)
> > > intent clearer
> > > - removed parts which had been commented out since chunk
> > > coalescation
> > > (8198423) and which would never really work, plus code which relied
> > > on it.
> > >
> > > Note: IMHO the value of these tests is a bit diminished and
> > > probably
> > > not
> > > worth the trouble of maintaining? To compensate for that I did add
> > > test_metaspace_allocation.cpp some time ago which is more thorough
> > > and less
> > > vulnerable against changes in the metaspace implementation.
> > >
> > > ----
> > >
> > > Tests: I stressed my patch locally (linux x64) with my own
> > > metaspace
> > > tests
> > > as well as hotspot/jtreg/runtime/*, including the
> > > SelectionResolution
> > > tests. Before pushing, I will put the patch through our nightlies.
> > >
> > > Thank you, Thomas
>
>