RFR(L) 8231610 Relocate the CDS archive if it cannot be mapped to the requested address
Jiangli Zhou
jianglizhou at google.com
Mon Nov 11 01:14:40 UTC 2019
On Sun, Nov 10, 2019, 3:13 PM Ioi Lam <ioi.lam at oracle.com> wrote:
>
>
> On 11/9/19 8:25 PM, Jiangli Zhou wrote:
> > Hi Ioi,
> >
> > On Fri, Nov 8, 2019 at 1:35 PM Ioi Lam <ioi.lam at oracle.com> wrote:
> >> Hi Jiangli,
> >>
> >> Thanks for your comments. Please see my replies in-line:
> >>
> >> On 11/7/19 6:34 PM, Jiangli Zhou wrote:
> >>> On Thu, Nov 7, 2019 at 6:11 PM Jiangli Zhou <jianglizhou at google.com>
> wrote:
> >>>> I looked both 05.full and 06.delta webrevs. They look good.
> >>>>
> >>>> I still feel a bit uneasy about the potential runtime impact when data
> >>>> does get relocated. Long running apps/services may be shy away from
> >>>> enabling archive at runtime, if there is a detectable overhead even
> >>>> though it may only occur rarely. As relocation is enabled by default
> >>>> and users cannot turn it off, disabling with -Xshare:off entirely
> >>>> would become the only choice. Could you please create a new RFE
> >>>> (possibly with higher priority) to investigate the potential effect,
> >>>> or provide an option for users to opt-in relocation with the
> >>>> command-line switch?
> >> I created https://bugs.openjdk.java.net/browse/JDK-8233862
> >> Investigate performance benefit of relocating CDS archive to under 32G
> >>
> >> As I noted in the bug report, I ran benchmarks with CDS relocation
> >> on/off, and there's no sign of regression when the CDS archive is
> >> relocated. Please see the bug report for how to configure the VM to do
> >> the comparison.
> >>
> >> As you said before: "When enabling CDS we [google] noticed a small
> >> runtime overhead in JDK 11 recently with a benchmark. After I backported
> >> JDK-8213713 to 11, it seemed to reduce the runtime overhead that the
> >> benchmark was experiencing":
> >>
> >> Can you confirm whether this is stock JDK 11 or a special google build?
> >> Which test case did you use? Is it possible for you to run the tests
> >> again (using the exact before/after bits that you had when backporting
> >> JDK-8213713)? Can you check if narrow_klass_base and narrow_klass_shift
> >> are the same in your before/after builds?
> > Thanks for creating the RFE.
> >
> > JDK-8213713 closes the 1G gap between the shared space and class space
> > and everything else is unaffected. The compressed class base and shift
> > were the same for before and after applying JDK-8213713. The effect
> > was statistically observed for the benchmark since the difference was
> > very small and could be within noise level for single run comparison.
> > A small difference could still be important for some use cases so it
> > needs to be taken into consideration when designing and implementing
> > new changes.
>
> Hi Jiangli,
>
> Thanks for taking the time for doing the performance measurements.
>
> I also ran benchmarks in all 3 modes (no CDS, CDS without relocation,
> CDS with relocation), and did not see any significant performance with
> Octane-DeltaBlue, Octane-NavierStokes, SPECjbb2005-Tuned,
> JFR-SPECjbb2005-Tuned, SPECjvm2008-Serial-G1 and Tools-Javac-Hello.
>
>
> >
> > A new command-line for archived metadata relocation may still be
> > valuable. It would also be helpful for debugging and diagnosis.
> >
>
> How about a diagnostic flag ArchiveRelocationMode:
>
> 0: (default) first map at preferred address, and if unsuccessful, map to
> alternative address;
> 1: always map to alternative address;
> 2: always map at preferred address, and if unsuccessful, do not map the
> archive;
>
> 1 is for testing relocation, as well as for easy performance measurement
> (replaces the use of -XX:SharedBaseAddress=0 in my current patch.).
> 2 is for avoiding potential regression that may be introduced by
> relocation (revert to JDK 13 behavior).
>
> What do you think? If you like this I'll open a CSR.
>
That sounds good to me!
Regards,
Jiangli
> Thanks
> - Ioi
>
>
>
> >>> Forgot to say that when Java heap can fit into low 32G space, it takes
> >>> the class space size into account and leaves need space right above
> >>> (also in low 32G space) when reserving heap, for !UseSharedSpace. In
> >>> that case, it's more likely the class data and heap data can be
> >>> colocated successfully.
> >> The reason is not for "colocation". It's so that narrow_klass_base can
> >> be zero, and the klass pointer can be uncompressed with a shift (without
> >> also doing an addition).
> >>
> >> But with CDS enabled, we always hard code to use non-zero
> >> narrow_klass_base and 3 bit shift (for AOT). So by just relocating the
> >> CDS archive to under 32GB, without modifying how CDS handles
> >> narrow_klass_base/shift, I don't think we can expect any benefit.
> > I experimented with mapping the shared space in low 32G and placed
> > right above the Java heap. The class space was also allocated in the
> > low 32G space and after the mapped shared space in the experiment. The
> > compress class encoding was using 0 base and 3 shift, which was the
> > same as the encoding when CDS was disabled. I didn't observe runtime
> > performance difference when comparing that specific configuration with
> > the normal CDS mapping scheme (the shared space start at 32G and the
> > encoding is non-zero base and 3 shift).
> >
> > Thanks,
> > Jiangli
> >> For modern architectures, I am not aware of any inherent speed benefit
> >> simply by putting data (in our case much larger than a page) "close to
> >> each other" in the virtual address space. If you have any reference of
> >> that, please let me know.
> >>
> >> Thanks
> >> - Ioi
> >>
> >>> Thanks,
> >>> Jiangli
> >>>
> >>>> Regards,
> >>>> Jiangli
> >>>>
> >>>> On Thu, Nov 7, 2019 at 4:22 PM Ioi Lam <ioi.lam at oracle.com> wrote:
> >>>>> Hi Coleen,
> >>>>>
> >>>>> Thanks for the review. Here's an webrev that has incorporated your
> >>>>> suggestions:
> >>>>>
> >>>>>
> http://cr.openjdk.java.net/~iklam/jdk14/8231610-relocate-cds-archive.v06-delta/
> >>>>>
> >>>>> Please see comments in-line
> >>>>>
> >>>>> On 11/7/19 2:46 PM, coleen.phillimore at oracle.com wrote:
> >>>>>> Hi, I've done a more high level code review of this and it looks
> good!
> >>>>>>
> >>>>>>
> http://cr.openjdk.java.net/~iklam/jdk14/8231610-relocate-cds-archive.v05/src/hotspot/share/memory/archiveUtils.hpp.html
> >>>>>>
> >>>>>>
> >>>>>> I think these classes require comments on what they do and why. The
> >>>>>> comments you sent me offline look good.
> >>>>> I added more comments for ArchivePtrMarker::_compacted per your
> offline
> >>>>> request.
> >>>>>
> >>>>>> Also .hpp files shouldn't include .inline.hpp files, like
> >>>>>> bitMap.inline.hpp. Hopefully it's just a case of moving do_bit()
> into
> >>>>>> the cpp file.
> >>>>> I moved the do_bit() function into archiveUtils.inline.hpp, since is
> >>>>> used by 3 .cpp files, and performance is important.
> >>>>>
> >>>>>> I wonder if the exception list of classes to exclude should be a
> >>>>>> function in javaClasses.hpp/cpp where the explanation would make
> more
> >>>>>> sense? ie bool
> >>>>>> JavaClasses::has_injected_native_pointers(InstanceKlass* k);
> >>>>> I moved the checking code to javaClasses.cpp. Since we do (partially)
> >>>>> support java.lang.Class, which has injected native pointers, I named
> the
> >>>>> function as JavaClasses::is_supported_for_archiving instead. I also
> >>>>> massaged the comments a little for clarification.
> >>>>>
> >>>>>> Is there already an RFE to move the DumpSharedSpaces output from
> >>>>>> tty->print() to log_info() ?
> >>>>> I created https://bugs.openjdk.java.net/browse/JDK-8233826 (Change
> CDS
> >>>>> dumping tty->print_cr() to unified logging).
> >>>>>
> >>>>> Thanks
> >>>>> - Ioi
> >>>>>
> >>>>>> Thanks,
> >>>>>> Coleen
> >>>>>>
> >>>>>> On 11/6/19 4:17 PM, Ioi Lam wrote:
> >>>>>>> Hi Jiangli,
> >>>>>>>
> >>>>>>> I've uploaded the webrev after integrating your comments:
> >>>>>>>
> >>>>>>>
> http://cr.openjdk.java.net/~iklam/jdk14/8231610-relocate-cds-archive.v05/
> >>>>>>>
> >>>>>>>
> http://cr.openjdk.java.net/~iklam/jdk14/8231610-relocate-cds-archive.v05-delta/
> >>>>>>>
> >>>>>>>
> >>>>>>> Please see more replies below:
> >>>>>>>
> >>>>>>>
> >>>>>>> On 11/4/19 5:52 PM, Jiangli Zhou wrote:
> >>>>>>>> On Sun, Nov 3, 2019 at 10:27 PM Ioi Lam <ioi.lam at oracle.com
> >>>>>>>> <mailto:ioi.lam at oracle.com>> wrote:
> >>>>>>>>
> >>>>>>>> Hi Jiangli,
> >>>>>>>>
> >>>>>>>> Thank you so much for spending time reviewing this RFE!
> >>>>>>>>
> >>>>>>>> On 11/3/19 6:34 PM, Jiangli Zhou wrote:
> >>>>>>>> > Hi Ioi,
> >>>>>>>> >
> >>>>>>>> > Sorry for the delay again. Will try to put this on the
> top of my
> >>>>>>>> list
> >>>>>>>> > next week and reduce the turn-around time. The updates
> look
> >>>>>>>> good in
> >>>>>>>> > general.
> >>>>>>>> >
> >>>>>>>> > We might want to have a better strategy when choosing
> metadata
> >>>>>>>> > relocation address (when relocation is needed). Some
> >>>>>>>> > applications/benchmarks may be more sensitive to cache
> >>>>>>>> locality and
> >>>>>>>> > memory/data layout. There was a bug,
> >>>>>>>> > https://bugs.openjdk.java.net/browse/JDK-8213713 that
> caused
> >>>>>>>> 1G gap
> >>>>>>>> > between Java heap data and metadata before JDK 12. The gap
> >>>>>>>> seemed to
> >>>>>>>> > cause a small but noticeable runtime effect in one case
> that I
> >>>>>>>> came
> >>>>>>>> > across.
> >>>>>>>>
> >>>>>>>> I guess you're saying we should try to relocate the archive
> into
> >>>>>>>> somewhere under 32GB?
> >>>>>>>>
> >>>>>>>>
> >>>>>>>> I don't yet have sufficient data that determins if mapping at low
> >>>>>>>> 32G produces better runtime performance. I experimented with that,
> >>>>>>>> but didn't see noticeable difference when comparing to mapping at
> >>>>>>>> the current default address. It doesn't hurt, I think. So it may
> be
> >>>>>>>> a better choice than relocating to a random address in high 32G
> >>>>>>>> space (when Java heap is in low 32G address space).
> >>>>>>> Maybe we should reconsider this when we have more concrete data for
> >>>>>>> the benefits of moving the compressed class space to under 32G.
> >>>>>>>
> >>>>>>> Please note that in metaspace.cpp, when CDS is disabled and the VM
> >>>>>>> fails to allocate the class space at the requested address
> >>>>>>> (0x7c000000 for 16GB heap), it also just allocates from a random
> >>>>>>> address (without trying to to search under 32GB):
> >>>>>>>
> >>>>>>>
> http://hg.openjdk.java.net/jdk/jdk/annotate/e767fa6a1d45/src/hotspot/share/memory/metaspace.cpp#l1128
> >>>>>>>
> >>>>>>>
> >>>>>>> This code has been there since 2013 and we have not seen any
> issues.
> >>>>>>>
> >>>>>>>
> >>>>>>>
> >>>>>>>
> >>>>>>>> Could you elaborate more about the performance issue,
> especially
> >>>>>>>> about
> >>>>>>>> cache locality? I looked at JDK-8213713 but it didn't
> mention about
> >>>>>>>> performance.
> >>>>>>>>
> >>>>>>>>
> >>>>>>>> When enabling CDS we noticed a small runtime overhead in JDK 11
> >>>>>>>> recently with a benchmark. After I backported JDK-8213713 to 11,
> it
> >>>>>>>> seemed to reduce the runtime overhead that the benchmark was
> >>>>>>>> experiencing.
> >>>>>>>>
> >>>>>>>>
> >>>>>>>> Also, by default, we have non-zero narrow_klass_base and
> >>>>>>>> narrow_klass_shift = 3, and archive relocation doesn't
> change that:
> >>>>>>>>
> >>>>>>>> $ java -Xlog:cds=debug -version
> >>>>>>>> ... narrow_klass_base = 0x0000000800000000,
> narrow_klass_shift = 3
> >>>>>>>> $ java -Xlog:cds=debug -XX:SharedBaseAddress=0 -version
> >>>>>>>> ... narrow_klass_base = 0x00007f1e8b499000,
> narrow_klass_shift = 3
> >>>>>>>>
> >>>>>>>> We always use narrow_klass_shift due to this:
> >>>>>>>>
> >>>>>>>> // CDS uses LogKlassAlignmentInBytes for
> narrow_klass_shift. See
> >>>>>>>> //
> >>>>>>>> MetaspaceShared::initialize_dumptime_shared_and_meta_spaces() for
> >>>>>>>> // how dump time narrow_klass_shift is set. Although,
> CDS can
> >>>>>>>> work
> >>>>>>>> // with zero-shift mode also, to be consistent with AOT
> it uses
> >>>>>>>> // LogKlassAlignmentInBytes for klass shift so archived
> java
> >>>>>>>> heap objects
> >>>>>>>> // can be used at same time as AOT code.
> >>>>>>>> if (!UseSharedSpaces
> >>>>>>>> && (uint64_t)(higher_address - lower_base) <=
> >>>>>>>> UnscaledClassSpaceMax) {
> >>>>>>>> CompressedKlassPointers::set_shift(0);
> >>>>>>>> } else {
> >>>>>>>> CompressedKlassPointers::set_shift(LogKlassAlignmentInBytes);
> >>>>>>>> }
> >>>>>>>>
> >>>>>>>>
> >>>>>>>> Right. If we relocate to low 32G space, it needs to make sure that
> >>>>>>>> the range containing the mapped class data and class space must be
> >>>>>>>> encodable.
> >>>>>>>>
> >>>>>>>>
> >>>>>>>> > Here are some additional comments (minor).
> >>>>>>>> >
> >>>>>>>> > Could you please fix the long lines in the following?
> >>>>>>>> >
> >>>>>>>> > 1237 void
> >>>>>>>>
> java_lang_Class::update_archived_primitive_mirror_native_pointers(oop
> >>>>>>>> > archived_mirror) {
> >>>>>>>> > 1238 if (MetaspaceShared::relocation_delta() != 0) {
> >>>>>>>> > 1239
> assert(archived_mirror->metadata_field(_klass_offset) ==
> >>>>>>>> > NULL, "must be for primitive class");
> >>>>>>>> > 1240
> >>>>>>>> > 1241 Klass* ak =
> >>>>>>>> >
> ((Klass*)archived_mirror->metadata_field(_array_klass_offset));
> >>>>>>>> > 1242 if (ak != NULL) {
> >>>>>>>> > 1243
> archived_mirror->metadata_field_put(_array_klass_offset,
> >>>>>>>> > (Klass*)(address(ak) +
> MetaspaceShared::relocation_delta()));
> >>>>>>>> > 1244 }
> >>>>>>>> > 1245 }
> >>>>>>>> > 1246 }
> >>>>>>>> >
> >>>>>>>> > src/hotspot/share/memory/dynamicArchive.cpp
> >>>>>>>> >
> >>>>>>>> > 889 Thread* THREAD = Thread::current();
> >>>>>>>> > 890 Method::sort_methods(ik->methods(),
> /*set_idnums=*/true,
> >>>>>>>> > dynamic_dump_method_comparator);
> >>>>>>>> > 891 if (ik->default_methods() != NULL) {
> >>>>>>>> > 892 Method::sort_methods(ik->default_methods(),
> >>>>>>>> > /*set_idnums=*/false, dynamic_dump_method_comparator);
> >>>>>>>> > 893 }
> >>>>>>>> >
> >>>>>>>>
> >>>>>>>> OK will do.
> >>>>>>>>
> >>>>>>>> > Please see inlined comments below.
> >>>>>>>> >
> >>>>>>>> > On Mon, Oct 28, 2019 at 9:05 PM Ioi Lam <
> ioi.lam at oracle.com
> >>>>>>>> <mailto:ioi.lam at oracle.com>> wrote:
> >>>>>>>> >> Hi Jiangli,
> >>>>>>>> >>
> >>>>>>>> >> Thanks for the review. I've updated the patch according
> to your
> >>>>>>>> comments:
> >>>>>>>> >>
> >>>>>>>> >>
> >>>>>>>>
> http://cr.openjdk.java.net/~iklam/jdk14/8231610-relocate-cds-archive.v04/
> >>>>>>>>
> >>>>>>>> >>
> >>>>>>>>
> http://cr.openjdk.java.net/~iklam/jdk14/8231610-relocate-cds-archive.v04.delta/
> >>>>>>>>
> >>>>>>>> >>
> >>>>>>>> >> (the delta is on top of
> 8231610-relocate-cds-archive.v03.delta
> >>>>>>>> in my
> >>>>>>>> >> reply to Calvin's comments).
> >>>>>>>> >>
> >>>>>>>> >> On 10/27/19 9:13 PM, Jiangli Zhou wrote:
> >>>>>>>> >>> Hi Ioi,
> >>>>>>>> >>>
> >>>>>>>> >>> Sorry for the delay. Here are my remaining comments.
> >>>>>>>> >>>
> >>>>>>>> >>> - src/hotspot/share/memory/dynamicArchive.cpp
> >>>>>>>> >>>
> >>>>>>>> >>> 128 static intx _method_comparator_name_delta;
> >>>>>>>> >>>
> >>>>>>>> >>> The name of the above variable is confusing. It's the
> value of
> >>>>>>>> >>> _buffer_to_target_delta. It's better to
> _buffer_to_target_delta
> >>>>>>>> >>> directly.
> >>>>>>>> >> _buffer_to_target_delta is a non-static field, but
> >>>>>>>> >> dynamic_dump_method_comparator() must be a static
> function so
> >>>>>>>> it can't
> >>>>>>>> >> use the non-static field easily.
> >>>>>>>> >
> >>>>>>>> > It sounds like an issue. _buffer_to_target_delta was made
> as a
> >>>>>>>> > non-static mostly because we might support more than one
> dynamic
> >>>>>>>> > archives in the future. However, today's usages bake in an
> >>>>>>>> assumption
> >>>>>>>> > that _buffer_to_target_delta is a singleton value. It is
> >>>>>>>> cleaner to
> >>>>>>>> > either make _buffer_to_target_delta as a static variable
> for
> >>>>>>>> now, or
> >>>>>>>> > adding an access API in DynamicArchiveBuilder to allow
> other
> >>>>>>>> code to
> >>>>>>>> > properly and correctly use the value.
> >>>>>>>>
> >>>>>>>> OK, I'll move it to a static variable.
> >>>>>>>>
> >>>>>>>> >
> >>>>>>>> >>> Also, we can do a quick pointer comparison of 'a_name'
> and
> >>>>>>>> >>> 'b_name' first before adjusting the pointers.
> >>>>>>>> >> I added this:
> >>>>>>>> >>
> >>>>>>>> >> if (a_name == b_name) {
> >>>>>>>> >> return 0;
> >>>>>>>> >> }
> >>>>>>>> >>
> >>>>>>>> >>> ---
> >>>>>>>> >>>
> >>>>>>>> >>> 934 void
> DynamicArchiveBuilder::relocate_buffer_to_target() {
> >>>>>>>> >>> ...
> >>>>>>>> >>> 944
> >>>>>>>> >>> 945 ArchivePtrMarker::compact(relocatable_base,
> >>>>>>>> relocatable_end);
> >>>>>>>> >>> ...
> >>>>>>>> >>>
> >>>>>>>> >>> 974 SharedDataRelocator
> patcher((address*)patch_base,
> >>>>>>>> >>> (address*)patch_end, valid_old_base, valid_old_end,
> >>>>>>>> >>> 975 valid_new_base, valid_new_end, addr_delta);
> >>>>>>>> >>> 976 ArchivePtrMarker::ptrmap()->iterate(&patcher);
> >>>>>>>> >>>
> >>>>>>>> >>> Could we reduce the number of data re-iterations to help
> >>>>>>>> archive
> >>>>>>>> >>> dumping performance. The ArchivePtrMarker::compact
> operation
> >>>>>>>> can be
> >>>>>>>> >>> combined with the patching iteration.
> >>>>>>>> ArchivePtrMarker::compact API
> >>>>>>>> >>> can be removed.
> >>>>>>>> >> That's a good idea. I implemented it using a template
> parameter
> >>>>>>>> so that
> >>>>>>>> >> we can have max performance when relocating the archive
> at run
> >>>>>>>> time.
> >>>>>>>> >>
> >>>>>>>> >> I added comments to explain why the relocation is done
> here. The
> >>>>>>>> >> relocation is pretty rare (only when the base archive
> was not
> >>>>>>>> mapped at
> >>>>>>>> >> the default location).
> >>>>>>>> >>
> >>>>>>>> >>> ---
> >>>>>>>> >>>
> >>>>>>>> >>> 967 address valid_new_base =
> >>>>>>>> >>> (address)Arguments::default_SharedBaseAddress();
> >>>>>>>> >>> 968 address valid_new_end = valid_new_base +
> >>>>>>>> base_plus_top_size;
> >>>>>>>> >>>
> >>>>>>>> >>> The debugging only code can be included under #ifdef
> ASSERT.
> >>>>>>>> >> These values are actually also used in debug logging so
> they
> >>>>>>>> can't be
> >>>>>>>> >> ifdef'ed out.
> >>>>>>>> >>
> >>>>>>>> >> Also, the c++ compiler is pretty good with eliding code
> >>>>>>>> that's no
> >>>>>>>> >> actually used. If I comment out all the logging code in
> >>>>>>>> >> DynamicArchiveBuilder::relocate_buffer_to_target() and
> >>>>>>>> >> SharedDataRelocator, gcc elides all the unused fields
> and their
> >>>>>>>> >> assignments. So no code is generated for this, etc.
> >>>>>>>> >>
> >>>>>>>> >> address valid_new_base =
> >>>>>>>> >> (address)Arguments::default_SharedBaseAddress();
> >>>>>>>> >>
> >>>>>>>> >> Since #ifdef ASSERT makes the code harder to read, I
> think we
> >>>>>>>> should use
> >>>>>>>> >> it only when really necessary.
> >>>>>>>> > It seems cleaner to get rid of these debugging only
> variables, by
> >>>>>>>> > using 'relocatable_base' and
> >>>>>>>> > '(address)Arguments::default_SharedBaseAddress()' in the
> logging
> >>>>>>>> code.
> >>>>>>>>
> >>>>>>>> SharedDataRelocator is used under 3 different situations.
> These six
> >>>>>>>> variables (patch_base, patch_end, valid_old_base,
> valid_old_end,
> >>>>>>>> valid_new_base, valid_new_end) describes what is being
> patched,
> >>>>>>>> and what
> >>>>>>>> the expectations are, for each situation. The code will be
> hard to
> >>>>>>>> understand without them.
> >>>>>>>>
> >>>>>>>> Please note there's also logging code in the
> SharedDataRelocator
> >>>>>>>> constructor that prints out these values.
> >>>>>>>>
> >>>>>>>> I think I'll just remove the 'debug only' comment to avoid
> >>>>>>>> confusion.
> >>>>>>>>
> >>>>>>>>
> >>>>>>>> Ok.
> >>>>>>>>
> >>>>>>>>
> >>>>>>>> >
> >>>>>>>> >>> ---
> >>>>>>>> >>>
> >>>>>>>> >>> 993
> >>>>>>>> dynamic_info->write_bitmap_region(ArchivePtrMarker::ptrmap());
> >>>>>>>> >>>
> >>>>>>>> >>> We could combine the archived heap data bitmap into the
> new
> >>>>>>>> region as
> >>>>>>>> >>> well? It can be handled as a separate RFE.
> >>>>>>>> >> I've filed
> https://bugs.openjdk.java.net/browse/JDK-8233093
> >>>>>>>> >>
> >>>>>>>> >>> - src/hotspot/share/memory/filemap.cpp
> >>>>>>>> >>>
> >>>>>>>> >>> 1038 if (is_static()) {
> >>>>>>>> >>> 1039 if (errno == ENOENT) {
> >>>>>>>> >>> 1040 // Not locating the shared archive is ok.
> >>>>>>>> >>> 1041 fail_continue("Specified shared archive
> not found
> >>>>>>>> (%s).",
> >>>>>>>> >>> _full_path);
> >>>>>>>> >>> 1042 } else {
> >>>>>>>> >>> 1043 fail_continue("Failed to open shared
> archive file
> >>>>>>>> (%s).",
> >>>>>>>> >>> 1044 os::strerror(errno));
> >>>>>>>> >>> 1045 }
> >>>>>>>> >>> 1046 } else {
> >>>>>>>> >>> 1047 log_warning(cds, dynamic)("specified dynamic
> archive
> >>>>>>>> >>> doesn't exist: %s", _full_path);
> >>>>>>>> >>> 1048 }
> >>>>>>>> >>>
> >>>>>>>> >>> If the top layer is explicitly specified by the user, a
> >>>>>>>> warning does
> >>>>>>>> >>> not seem to be a proper behavior if the VM fails to
> open the
> >>>>>>>> archive
> >>>>>>>> >>> file.
> >>>>>>>> >>>
> >>>>>>>> >>> If might be better to handle the relocation unrelated
> code in
> >>>>>>>> separate
> >>>>>>>> >>> changeset and track with a separate RFE.
> >>>>>>>> >> This code was moved from
> >>>>>>>> >>
> >>>>>>>> >>
> >>>>>>>>
> http://hg.openjdk.java.net/jdk/jdk/file/d3382812b788/src/hotspot/share/memory/dynamicArchive.cpp#l1070
> >>>>>>>>
> >>>>>>>> >>
> >>>>>>>> >> so I am not changing the behavior. If you want, we can
> file an
> >>>>>>>> REF to
> >>>>>>>> >> change the behavior.
> >>>>>>>> > Ok. A new RFE sounds like the right thing to re-evaluable
> the
> >>>>>>>> usage
> >>>>>>>> > issue here. Thanks.
> >>>>>>>>
> >>>>>>>> I created https://bugs.openjdk.java.net/browse/JDK-8233446
> >>>>>>>>
> >>>>>>>> >>> ---
> >>>>>>>> >>>
> >>>>>>>> >>> 1148 void FileMapInfo::write_region(int region, char*
> base,
> >>>>>>>> size_t size,
> >>>>>>>> >>> 1149 bool read_only, bool
> >>>>>>>> allow_exec) {
> >>>>>>>> >>> ...
> >>>>>>>> >>> 1154
> >>>>>>>> >>> 1155 if (region == MetaspaceShared::bm) {
> >>>>>>>> >>> 1156 target_base = NULL;
> >>>>>>>> >>> 1157 } else if (DynamicDumpSharedSpaces) {
> >>>>>>>> >>>
> >>>>>>>> >>> It's not too clear to me how the bitmap (bm) region is
> handled
> >>>>>>>> for the
> >>>>>>>> >>> base layer and top layer. Could you please explain?
> >>>>>>>> >> The bm region for both layers are mapped at an address
> picked
> >>>>>>>> by the OS:
> >>>>>>>> >>
> >>>>>>>> >> char* FileMapInfo::map_relocation_bitmap(size_t&
> bitmap_size) {
> >>>>>>>> >> FileMapRegion* si = space_at(MetaspaceShared::bm);
> >>>>>>>> >> bitmap_size = si->used_aligned();
> >>>>>>>> >> bool read_only = true, allow_exec = false;
> >>>>>>>> >> char* requested_addr = NULL; // allow OS to pick any
> >>>>>>>> location
> >>>>>>>> >> char* bitmap_base = os::map_memory(_fd, _full_path,
> >>>>>>>> si->file_offset(),
> >>>>>>>> >> requested_addr, bitmap_size,
> >>>>>>>> >> read_only, allow_exec);
> >>>>>>>> >>
> >>>>>>>> > Ok, after staring at the code for a few seconds I saw
> that's
> >>>>>>>> intended.
> >>>>>>>> > If the current region is 'bm', then the 'target_base' is
> NULL
> >>>>>>>> > regardless if it's static or dynamic archive. Otherwise,
> the
> >>>>>>>> > 'target_base' is handled differently for the static and
> dynamic
> >>>>>>>> case.
> >>>>>>>> > The following would be cleaner and has better reliability.
> >>>>>>>> >
> >>>>>>>> > char* target_base = NULL;
> >>>>>>>> >
> >>>>>>>> > // The target_base is NULL for 'bm' region.
> >>>>>>>> > if (!region == MetaspaceShared::bm) {
> >>>>>>>> > if (DynamicDumpSharedSpaces) {
> >>>>>>>> > assert(!HeapShared::is_heap_region(region),
> "dynamic
> >>>>>>>> archive
> >>>>>>>> > doesn't support heap regions");
> >>>>>>>> > target_base =
> DynamicArchive::buffer_to_target(base);
> >>>>>>>> > } else {
> >>>>>>>> > target_base = base;
> >>>>>>>> > }
> >>>>>>>> > }
> >>>>>>>>
> >>>>>>>> How about this?
> >>>>>>>>
> >>>>>>>> char* target_base;
> >>>>>>>> if (region == MetaspaceShared::bm) {
> >>>>>>>> target_base = NULL; // always NULL for bm region.
> >>>>>>>> } else {
> >>>>>>>> if (DynamicDumpSharedSpaces) {
> >>>>>>>> assert(!HeapShared::is_heap_region(region),
> "dynamic
> >>>>>>>> archive
> >>>>>>>> doesn't support heap regions");
> >>>>>>>> target_base =
> DynamicArchive::buffer_to_target(base);
> >>>>>>>> } else {
> >>>>>>>> target_base = base;
> >>>>>>>> }
> >>>>>>>> }
> >>>>>>>>
> >>>>>>>>
> >>>>>>>> No objection If you prefer the extra 'else' block.
> >>>>>>>>
> >>>>>>>>
> >>>>>>>> >
> >>>>>>>> >>> ---
> >>>>>>>> >>>
> >>>>>>>> >>> 1362
> >>>>>>>>
> DEBUG_ONLY(header()->set_mapped_base_address((char*)(uintptr_t)0xdeadbeef);)
> >>>>>>>>
> >>>>>>>> >>>
> >>>>>>>> >>> Could you please explain the above?
> >>>>>>>> >> I added the comments
> >>>>>>>> >>
> >>>>>>>> >> // Make sure we don't attempt to use
> >>>>>>>> header()->mapped_base_address()
> >>>>>>>> >> unless
> >>>>>>>> >> // it's been successfully mapped.
> >>>>>>>> >>
> >>>>>>>>
> DEBUG_ONLY(header()->set_mapped_base_address((char*)(uintptr_t)0xdeadbeef);)
> >>>>>>>>
> >>>>>>>> >>
> >>>>>>>> >>> ---
> >>>>>>>> >>>
> >>>>>>>> >>> 1359 FileMapRegion* last_region = NULL;
> >>>>>>>> >>>
> >>>>>>>> >>> 1371 if (last_region != NULL) {
> >>>>>>>> >>> 1372 // Ensure that the OS won't be able to
> allocate new
> >>>>>>>> memory
> >>>>>>>> >>> spaces between any mapped
> >>>>>>>> >>> 1373 // regions, or else it would mess up the
> simple
> >>>>>>>> comparision
> >>>>>>>> >>> in MetaspaceObj::is_shared().
> >>>>>>>> >>> 1374 assert(si->mapped_base() ==
> >>>>>>>> last_region->mapped_end(),
> >>>>>>>> >>> "must have no gaps");
> >>>>>>>> >>>
> >>>>>>>> >>> 1379 last_region = si;
> >>>>>>>> >>>
> >>>>>>>> >>> Can you please place 'last_region' related code under
> #ifdef
> >>>>>>>> ASSERT?
> >>>>>>>> >> I think that will make the code more cluttered. The
> compiler
> >>>>>>>> will
> >>>>>>>> >> optimize out that away.
> >>>>>>>> > It's cleaner to define debugging only variable for
> debugging only
> >>>>>>>> > builds. You can wrapper it and related usage with
> DEBUG_ONLY.
> >>>>>>>>
> >>>>>>>> OK, will do.
> >>>>>>>>
> >>>>>>>> >
> >>>>>>>> >>> ---
> >>>>>>>> >>>
> >>>>>>>> >>> 1478 char* FileMapInfo::map_relocation_bitmap(size_t&
> >>>>>>>> bitmap_size) {
> >>>>>>>> >>> 1479 FileMapRegion* si =
> space_at(MetaspaceShared::bm);
> >>>>>>>> >>> 1480 bitmap_size = si->used_aligned();
> >>>>>>>> >>> 1481 bool read_only = true, allow_exec = false;
> >>>>>>>> >>> 1482 char* requested_addr = NULL; // allow OS to pick
> any
> >>>>>>>> location
> >>>>>>>> >>> 1483 char* bitmap_base = os::map_memory(_fd,
> _full_path,
> >>>>>>>> si->file_offset(),
> >>>>>>>> >>> 1484 requested_addr, bitmap_size,
> >>>>>>>> >>> read_only, allow_exec);
> >>>>>>>> >>>
> >>>>>>>> >>> We need to handle mapping failure here.
> >>>>>>>> >> It's handled here:
> >>>>>>>> >>
> >>>>>>>> >> bool FileMapInfo::relocate_pointers(intx addr_delta) {
> >>>>>>>> >> log_debug(cds, reloc)("runtime archive relocation
> start");
> >>>>>>>> >> size_t bitmap_size;
> >>>>>>>> >> char* bitmap_base =
> map_relocation_bitmap(bitmap_size);
> >>>>>>>> >> if (bitmap_base != NULL) {
> >>>>>>>> >> ...
> >>>>>>>> >> } else {
> >>>>>>>> >> log_error(cds)("failed to map relocation bitmap");
> >>>>>>>> >> return false;
> >>>>>>>> >> }
> >>>>>>>> >>
> >>>>>>>> > 'bitmap_base' is used immediately after map_memory(). So
> the
> >>>>>>>> check
> >>>>>>>> > needs to be done immediately after map_memory(), but not
> in the
> >>>>>>>> caller
> >>>>>>>> > of map_relocation_bitmap().
> >>>>>>>> >
> >>>>>>>> > 1490 char* bitmap_base = os::map_memory(_fd, _full_path,
> >>>>>>>> si->file_offset(),
> >>>>>>>> > 1491 requested_addr, bitmap_size,
> >>>>>>>> > read_only, allow_exec);
> >>>>>>>> > 1492
> >>>>>>>> > 1493 if (VerifySharedSpaces && bitmap_base != NULL &&
> >>>>>>>> > !region_crc_check(bitmap_base, bitmap_size, si->crc())) {
> >>>>>>>>
> >>>>>>>> OK, I'll fix that.
> >>>>>>>>
> >>>>>>>> >
> >>>>>>>> >
> >>>>>>>> >>> ---
> >>>>>>>> >>>
> >>>>>>>> >>> 1513 // debug only -- the current value of the
> pointers
> >>>>>>>> to be
> >>>>>>>> >>> patched must be within this
> >>>>>>>> >>> 1514 // range (i.e., must be between the requesed
> base
> >>>>>>>> address,
> >>>>>>>> >>> and the of the current archive).
> >>>>>>>> >>> 1515 // Note: top archive may point to objects in
> the base
> >>>>>>>> >>> archive, but not the other way around.
> >>>>>>>> >>> 1516 address valid_old_base =
> >>>>>>>> (address)header()->requested_base_address();
> >>>>>>>> >>> 1517 address valid_old_end = valid_old_base +
> >>>>>>>> mapping_end_offset();
> >>>>>>>> >>>
> >>>>>>>> >>> Please place all FileMapInfo::relocate_pointers
> debugging only
> >>>>>>>> code
> >>>>>>>> >>> under #ifdef ASSERT.
> >>>>>>>> >> Ditto about ifdef ASSERT
> >>>>>>>> >>
> >>>>>>>> >>> - src/hotspot/share/memory/heapShared.cpp
> >>>>>>>> >>>
> >>>>>>>> >>> 441 void
> >>>>>>>> HeapShared::initialize_from_archived_subgraph(Klass* k) {
> >>>>>>>> >>> 442 if (!open_archive_heap_region_mapped() ||
> >>>>>>>> !MetaspaceObj::is_shared(k)) {
> >>>>>>>> >>> 443 return; // nothing to do
> >>>>>>>> >>> 444 }
> >>>>>>>> >>>
> >>>>>>>> >>> When do we call
> HeapShared::initialize_from_archived_subgraph
> >>>>>>>> for a
> >>>>>>>> >>> klass that's not shared?
> >>>>>>>> >> I've removed the !MetaspaceObj::is_shared(k). I probably
> added
> >>>>>>>> that for
> >>>>>>>> >> debugging purposes only.
> >>>>>>>> >>
> >>>>>>>> >>> 616 DEBUG_ONLY({
> >>>>>>>> >>> 617 Klass* klass = orig_obj->klass();
> >>>>>>>> >>> 618 assert(klass !=
> >>>>>>>> SystemDictionary::Module_klass() &&
> >>>>>>>> >>> 619 klass !=
> >>>>>>>> SystemDictionary::ResolvedMethodName_klass() &&
> >>>>>>>> >>> 620 klass !=
> >>>>>>>> SystemDictionary::MemberName_klass() &&
> >>>>>>>> >>> 621 klass !=
> >>>>>>>> SystemDictionary::Context_klass() &&
> >>>>>>>> >>> 622 klass !=
> >>>>>>>> SystemDictionary::ClassLoader_klass(), "we
> >>>>>>>> >>> can only relocate metaspace object pointers inside
> >>>>>>>> java_lang_Class
> >>>>>>>> >>> instances");
> >>>>>>>> >>> 623 });
> >>>>>>>> >>>
> >>>>>>>> >>> Let's leave the above for a separate RFE. I think
> assert is not
> >>>>>>>> >>> sufficient for the check. Also, why ResolvedMethodName,
> >>>>>>>> Module and
> >>>>>>>> >>> MemberName cannot be part of the graph?
> >>>>>>>> >>>
> >>>>>>>> >>>
> >>>>>>>> >> I added the following comment:
> >>>>>>>> >>
> >>>>>>>> >> DEBUG_ONLY({
> >>>>>>>> >> // The following are classes in
> >>>>>>>> share/classfile/javaClasses.cpp
> >>>>>>>> >> that have injected native pointers
> >>>>>>>> >> // to metaspace objects. To support these
> classes, we
> >>>>>>>> need to add
> >>>>>>>> >> relocation code similar to
> >>>>>>>> >> //
> >>>>>>>> java_lang_Class::update_archived_mirror_native_pointers.
> >>>>>>>> >> Klass* klass = orig_obj->klass();
> >>>>>>>> >> assert(klass != SystemDictionary::Module_klass()
> &&
> >>>>>>>> >> klass !=
> >>>>>>>> SystemDictionary::ResolvedMethodName_klass() &&
> >>>>>>>> >>
> >>>>>>>> > It's too restrictive to exclude those objects from the
> archived
> >>>>>>>> object
> >>>>>>>> > graph because metadata relocation, since metadata
> relocation is
> >>>>>>>> rare.
> >>>>>>>> > The trade-off doesn't seem to buy us much.
> >>>>>>>> >
> >>>>>>>> > Do you plan to add the needed relocation code?
> >>>>>>>>
> >>>>>>>> I looked more into this. Actually we cannot handle these 5
> >>>>>>>> classes at
> >>>>>>>> all, even without archive relocation:
> >>>>>>>>
> >>>>>>>> [1] #define MODULE_INJECTED_FIELDS(macro) \
> >>>>>>>> macro(java_lang_Module, module_entry, intptr_signature,
> false)
> >>>>>>>>
> >>>>>>>> -> module_entry is malloc'ed
> >>>>>>>>
> >>>>>>>> [2] #define RESOLVEDMETHOD_INJECTED_FIELDS(macro) \
> >>>>>>>> macro(java_lang_invoke_ResolvedMethodName, vmholder,
> >>>>>>>> object_signature, false) \
> >>>>>>>> macro(java_lang_invoke_ResolvedMethodName, vmtarget,
> >>>>>>>> intptr_signature, false)
> >>>>>>>>
> >>>>>>>> -> these fields are related to method handles and lambda
> forms,
> >>>>>>>> etc.
> >>>>>>>> They can't be easily be archived without implementing
> lambda form
> >>>>>>>> archiving. (I did a prototype; it's very complex and
> fragile).
> >>>>>>>>
> >>>>>>>> [3] #define CALLSITECONTEXT_INJECTED_FIELDS(macro) \
> >>>>>>>> macro(java_lang_invoke_MethodHandleNatives_CallSiteContext,
> >>>>>>>> vmdependencies, intptr_signature, false) \
> >>>>>>>> macro(java_lang_invoke_MethodHandleNatives_CallSiteContext,
> >>>>>>>> last_cleanup, long_signature, false)
> >>>>>>>>
> >>>>>>>> -> vmdependencies is malloc'ed.
> >>>>>>>>
> >>>>>>>> [4] #define
> >>>>>>>> MEMBERNAME_INJECTED_FIELDS(macro) \
> >>>>>>>> macro(java_lang_invoke_MemberName, vmindex,
> intptr_signature,
> >>>>>>>> false)
> >>>>>>>>
> >>>>>>>> -> this one is probably OK. Despite being declared as
> >>>>>>>> 'intptr_signature', it seems to be used just as an integer.
> >>>>>>>> However,
> >>>>>>>> MemberNames are typically used with [2] and [3]. So let's
> just
> >>>>>>>> forbid it
> >>>>>>>> to be safe.
> >>>>>>>>
> >>>>>>>> [2] [3] [4] are not used directly by regular Java code and
> are
> >>>>>>>> unlikely
> >>>>>>>> to be referenced (directly or indirectly) by static fields
> (except
> >>>>>>>> for
> >>>>>>>> the static fields in the classes in java.lang.invoke, which
> we
> >>>>>>>> probably
> >>>>>>>> won't support for heap archiving due to the problem I
> described for
> >>>>>>>> [2]). Objects of these types are typically referenced via
> constant
> >>>>>>>> pool
> >>>>>>>> entries.
> >>>>>>>>
> >>>>>>>> [5] #define CLASSLOADER_INJECTED_FIELDS(macro) \
> >>>>>>>> macro(java_lang_ClassLoader, loader_data,
> intptr_signature,
> >>>>>>>> false)
> >>>>>>>>
> >>>>>>>> -> loader_data is malloc'ed.
> >>>>>>>>
> >>>>>>>> So, I will change the DEBUG_ONLY into a product-mode check,
> and
> >>>>>>>> quit
> >>>>>>>> dumping if these objects are found in the object subgraph.
> >>>>>>>>
> >>>>>>>>
> >>>>>>>> Sounds good. Can you please also add a comment with explanation.
> >>>>>>>>
> >>>>>>>> For ClassLoader and Module, it worth considering caching the
> >>>>>>>> additional native data some time in the future. Lois had suggested
> >>>>>>>> the Module part a while ago.
> >>>>>>> I think we can do that if/when we archive Modules directly into the
> >>>>>>> shared heap.
> >>>>>>>
> >>>>>>>
> >>>>>>>
> >>>>>>>>
> >>>>>>>>
> >>>>>>>>
> >>>>>>>> Maybe we should backport the check to older versions as
> well?
> >>>>>>>>
> >>>>>>>>
> >>>>>>>> We should discuss with Andrew Haley for backports to JDK 11 update
> >>>>>>>> releases. Since the current OpenJDK 11 only applies Java heap
> >>>>>>>> archiving to a restricted set of JDK library code, I think it is
> >>>>>>>> safe without the new check.
> >>>>>>>>
> >>>>>>>> For non-LTS releases, it might not be worthwhile as they may not
> be
> >>>>>>>> widely used?
> >>>>>>> I agree. FYI, we (Oracle) have no plan for backporting more types
> of
> >>>>>>> heap object archiving, so the decision would be up to whoever that
> >>>>>>> decides to do so.
> >>>>>>>
> >>>>>>> Thanks
> >>>>>>> - Ioi
> >>>>>>>
> >>>>>>>
> >>>>>>>> Thanks,
> >>>>>>>> Jiangli
> >>>>>>>>
> >>>>>>>>
> >>>>>>>> >
> >>>>>>>> >>> - src/hotspot/share/memory/metaspace.cpp
> >>>>>>>> >>>
> >>>>>>>> >>> 1036 metaspace_rs =
> >>>>>>>> ReservedSpace(compressed_class_space_size(),
> >>>>>>>> >>> 1037 _reserve_alignment,
> >>>>>>>> >>> 1038 large_pages,
> >>>>>>>> >>> 1039 requested_addr);
> >>>>>>>> >>>
> >>>>>>>> >>> Please fix indentation.
> >>>>>>>> >> Fixed.
> >>>>>>>> >>
> >>>>>>>> >>> - src/hotspot/share/memory/metaspaceClosure.hpp
> >>>>>>>> >>>
> >>>>>>>> >>> 78 enum SpecialRef {
> >>>>>>>> >>> 79 _method_entry_ref
> >>>>>>>> >>> 80 };
> >>>>>>>> >>>
> >>>>>>>> >>> Are there other pointers that are not references to
> >>>>>>>> MetaspaceObj? If
> >>>>>>>> >>> _method_entry_ref is the only type, it's probably not
> worth
> >>>>>>>> defining
> >>>>>>>> >>> SpecialRef?
> >>>>>>>> >> There may be more types in the future, so I want to have
> a
> >>>>>>>> stable API
> >>>>>>>> >> that can be easily expanded without touching all the
> code that
> >>>>>>>> uses it.
> >>>>>>>> >>
> >>>>>>>> >>
> >>>>>>>> >>> - src/hotspot/share/memory/metaspaceShared.hpp
> >>>>>>>> >>>
> >>>>>>>> >>> 42 enum MapArchiveResult {
> >>>>>>>> >>> 43 MAP_ARCHIVE_SUCCESS,
> >>>>>>>> >>> 44 MAP_ARCHIVE_MMAP_FAILURE,
> >>>>>>>> >>> 45 MAP_ARCHIVE_OTHER_FAILURE
> >>>>>>>> >>> 46 };
> >>>>>>>> >>>
> >>>>>>>> >>> If we want to define different failure types, it's
> probably
> >>>>>>>> worth
> >>>>>>>> >>> using separate types for relocation failure and
> validation
> >>>>>>>> failure.
> >>>>>>>> >> For now, I just need to distinguish between MMAP_FAILURE
> (where
> >>>>>>>> I should
> >>>>>>>> >> attempt to remap at an alternative address) and
> OTHER_FAILURE
> >>>>>>>> (where the
> >>>>>>>> >> CDS archive loading will fail -- due to validation error,
> >>>>>>>> insufficient
> >>>>>>>> >> memory, etc -- without attempting to remap.)
> >>>>>>>> >>
> >>>>>>>> >>> ---
> >>>>>>>> >>>
> >>>>>>>> >>> 193 static intx _mapping_delta; // FIXME rename
> >>>>>>>> >>>
> >>>>>>>> >>> How about _relocation_delta?
> >>>>>>>> >> Changed as suggested.
> >>>>>>>> >>
> >>>>>>>> >>> - src/hotspot/share/oops/instanceKlass
> >>>>>>>> >>>
> >>>>>>>> >>> 1573 bool InstanceKlass::_disable_method_binary_search
> = false;
> >>>>>>>> >>>
> >>>>>>>> >>> The use of _disable_method_binary_search is not
> necessary. You
> >>>>>>>> can use
> >>>>>>>> >>> DynamicDumpSharedSpaces for the purpose. That would
> make things
> >>>>>>>> >>> cleaner.
> >>>>>>>> >> If we always disable the binary search when
> >>>>>>>> DynamicDumpSharedSpaces is
> >>>>>>>> >> true, it will slow down normal execution of the Java
> program
> >>>>>>>> when
> >>>>>>>> >> -XX:ArchiveClassesAtExit has been specified, but the
> program
> >>>>>>>> hasn't exited.
> >>>>>>>> > Could you please add some comments to
> >>>>>>>> _disable_method_binary_search
> >>>>>>>> > with the above explanation? Thanks.
> >>>>>>>>
> >>>>>>>> OK
> >>>>>>>> >
> >>>>>>>> >>> -
> test/hotspot/jtreg/runtime/cds/SpaceUtilizationCheck.java
> >>>>>>>> >>>
> >>>>>>>> >>> 76 if (name.equals("s0") ||
> >>>>>>>> name.equals("s1")) {
> >>>>>>>> >>> 77 // String regions are
> listed at
> >>>>>>>> the end and
> >>>>>>>> >>> they may not be fully occupied.
> >>>>>>>> >>> 78 break;
> >>>>>>>> >>> 79 } else if
> (name.equals("bm")) {
> >>>>>>>> >>> 80 // Bitmap space does not
> have a
> >>>>>>>> requested address.
> >>>>>>>> >>> 81 break;
> >>>>>>>> >>>
> >>>>>>>> >>> It's not part of your change, but could you please fix
> line 76
> >>>>>>>> - 78
> >>>>>>>> >>> since it is trivial. It seems the lines can be removed.
> >>>>>>>> >> Removed.
> >>>>>>>> >>
> >>>>>>>> >>> - /src/hotspot/share/memory/archiveUtils.hpp
> >>>>>>>> >>> The file name does not match with the macro '#ifndef
> >>>>>>>> >>> SHARE_MEMORY_SHAREDDATARELOCATOR_HPP'. Could you please
> rename
> >>>>>>>> >>> archiveUtils.* ? archiveRelocator.hpp and
> >>>>>>>> archiveRelocator.cpp are
> >>>>>>>> >>> more descriptive.
> >>>>>>>> >> I named the file archiveUtils.hpp so we can move other
> misc
> >>>>>>>> stuff used
> >>>>>>>> >> by dumping into this file (e.g., DumpRegion,
> WriteClosure from
> >>>>>>>> >> metaspaceShared.hpp), since theses are not used by the
> majority
> >>>>>>>> of the
> >>>>>>>> >> files that use metaspaceShared.hpp.
> >>>>>>>> >>
> >>>>>>>> >> I fixed the ifdef.
> >>>>>>>> >>
> >>>>>>>> >>> - src/hotspot/share/memory/archiveUtils.cpp
> >>>>>>>> >>>
> >>>>>>>> >>> 36 void ArchivePtrMarker::initialize(CHeapBitMap*
> ptrmap,
> >>>>>>>> address*
> >>>>>>>> >>> ptr_base, address* ptr_end) {
> >>>>>>>> >>> 37 assert(_ptrmap == NULL, "initialize only
> once");
> >>>>>>>> >>> 38 _ptr_base = ptr_base;
> >>>>>>>> >>> 39 _ptr_end = ptr_end;
> >>>>>>>> >>> 40 _compacted = false;
> >>>>>>>> >>> 41 _ptrmap = ptrmap;
> >>>>>>>> >>> 42 _ptrmap->initialize(12 * M /
> sizeof(intptr_t)); //
> >>>>>>>> default
> >>>>>>>> >>> archive is about 12MB.
> >>>>>>>> >>> 43 }
> >>>>>>>> >>>
> >>>>>>>> >>> Could we do a better estimate here? We could
> guesstimate the
> >>>>>>>> size
> >>>>>>>> >>> based on the current used class space and metaspace
> size. It's
> >>>>>>>> okay if
> >>>>>>>> >>> a larger bitmap used, since it can be reduced after all
> >>>>>>>> marking are
> >>>>>>>> >>> done.
> >>>>>>>> >> The bitmap is automatically expanded when necessary in
> >>>>>>>> >> ArchivePtrMarker::mark_pointer(). It's only about 1/32
> or 1/64
> >>>>>>>> of the
> >>>>>>>> >> total archive size, so even if we do expand, the cost
> will be
> >>>>>>>> trivial.
> >>>>>>>> > The initial value is based on the default CDS archive.
> When
> >>>>>>>> dealing
> >>>>>>>> > with a really large archive, it would have to re-grow
> many times.
> >>>>>>>> > Also, using a hard-coded value is less desirable.
> >>>>>>>>
> >>>>>>>> OK, I changed it to the following
> >>>>>>>>
> >>>>>>>> // Use this as initial guesstimate. We should need less
> space
> >>>>>>>> in the
> >>>>>>>> // archive, but if we're wrong the bitmap will be
> expanded
> >>>>>>>> automatically.
> >>>>>>>> size_t estimated_archive_size =
> >>>>>>>> MetaspaceGC::capacity_until_GC();
> >>>>>>>> // But set it smaller in debug builds so we always test
> the
> >>>>>>>> expansion
> >>>>>>>> code.
> >>>>>>>> // (Default archive is about 12MB).
> >>>>>>>> DEBUG_ONLY(estimated_archive_size = 6 * M);
> >>>>>>>>
> >>>>>>>> // We need one bit per pointer in the archive.
> >>>>>>>> _ptrmap->initialize(estimated_archive_size /
> sizeof(intptr_t));
> >>>>>>>>
> >>>>>>>>
> >>>>>>>> Thanks!
> >>>>>>>> - Ioi
> >>>>>>>>
> >>>>>>>> >
> >>>>>>>> >>>
> >>>>>>>> >>>
> >>>>>>>> >>> On Wed, Oct 16, 2019 at 4:58 PM Jiangli Zhou
> >>>>>>>> <jianglizhou at google.com <mailto:jianglizhou at google.com>>
> wrote:
> >>>>>>>> >>>> Hi Ioi,
> >>>>>>>> >>>>
> >>>>>>>> >>>> This is another great step for CDS usability
> improvement.
> >>>>>>>> Thank you!
> >>>>>>>> >>>>
> >>>>>>>> >>>> I have a high level question (or request): could we
> consider
> >>>>>>>> >>>> separating the relocation work for 'direct' class
> metadata
> >>>>>>>> from other
> >>>>>>>> >>>> types of metadata (such as the shared system
> dictionary,
> >>>>>>>> symbol table,
> >>>>>>>> >>>> etc)? Initially we only relocate the tables and other
> >>>>>>>> archived global
> >>>>>>>> >>>> data. When each archived class is being loaded, we can
> >>>>>>>> relocate all
> >>>>>>>> >>>> the pointers within the current class. We could find
> the
> >>>>>>>> segment (for
> >>>>>>>> >>>> the current class) in the bitmap and update the
> pointers
> >>>>>>>> within the
> >>>>>>>> >>>> segment. That way we can reduce initial startup costs
> and
> >>>>>>>> also avoid
> >>>>>>>> >>>> relocating class data that's not used at runtime. In
> some
> >>>>>>>> real world
> >>>>>>>> >>>> large systems, an archive may contain extremely large
> >>>>>>>> number of
> >>>>>>>> >>>> classes.
> >>>>>>>> >>>>
> >>>>>>>> >>>> Following are partial review comments so we can move
> things
> >>>>>>>> forward.
> >>>>>>>> >>>> Still going through the rest of the changes.
> >>>>>>>> >>>>
> >>>>>>>> >>>> - src/hotspot/share/classfile/javaClasses.cpp
> >>>>>>>> >>>>
> >>>>>>>> >>>> 1218 void
> >>>>>>>> java_lang_Class::update_archived_mirror_native_pointers(oop
> >>>>>>>> >>>> archived_mirror) {
> >>>>>>>> >>>> 1219 Klass* k =
> >>>>>>>> ((Klass*)archived_mirror->metadata_field(_klass_offset));
> >>>>>>>> >>>> 1220 if (k != NULL) { // k is NULL for the primitive
> >>>>>>>> classes such as
> >>>>>>>> >>>> java.lang.Byte::TYPE <<<<<<<<<<<
> >>>>>>>> >>>> 1221
> archived_mirror->metadata_field_put(_klass_offset,
> >>>>>>>> >>>> (Klass*)(address(k) +
> MetaspaceShared::mapping_delta()));
> >>>>>>>> >>>> 1222 }
> >>>>>>>> >>>> 1223 ...
> >>>>>>>> >>>>
> >>>>>>>> >>>> Primitive type mirrors are handled separately. Could
> you
> >>>>>>>> please verify
> >>>>>>>> >>>> if this call path happens for primitive type mirror?
> >>>>>>>> >>>>
> >>>>>>>> >>>> To answer my question above, looks like you added the
> >>>>>>>> following, which
> >>>>>>>> >>>> is to be used for primitive type mirrors. That seems
> to be
> >>>>>>>> the reason
> >>>>>>>> >>>> why update_archived_mirror_native_pointers is trying
> to also
> >>>>>>>> cover
> >>>>>>>> >>>> primitive type. It better to have a separate API for
> >>>>>>>> primitive type
> >>>>>>>> >>>> mirror, which is cleaner. And, we also can replace the
> above
> >>>>>>>> check at
> >>>>>>>> >>>> line 1220 to be an assert for regular mirrors.
> >>>>>>>> >>>>
> >>>>>>>> >>>> +void ReadClosure::do_mirror_oop(oop *p) {
> >>>>>>>> >>>> + do_oop(p);
> >>>>>>>> >>>> + oop mirror = *p;
> >>>>>>>> >>>> + if (mirror != NULL) {
> >>>>>>>> >>>> +
> >>>>>>>> java_lang_Class::update_archived_mirror_native_pointers(mirror);
> >>>>>>>> >>>> + }
> >>>>>>>> >>>> +}
> >>>>>>>> >>>> +
> >>>>>>>> >>>>
> >>>>>>>> >>>> How about renaming
> update_archived_mirror_native_pointers to
> >>>>>>>> >>>> update_archived_mirror_klass_pointers.
> >>>>>>>> >>>>
> >>>>>>>> >>>> It would be good to pass the current klass as an
> argument.
> >>>>>>>> We can
> >>>>>>>> >>>> verify the relocated pointer matches with the current
> klass
> >>>>>>>> pointer.
> >>>>>>>> >>>>
> >>>>>>>> >>>> We should also check if relocation is necessary before
> >>>>>>>> spending cycles
> >>>>>>>> >>>> to obtain the
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