Hi Ioi ,
Yes I looked a bit at space reduction but the effect is very small .
I was noticing the "mixture" of UseSharedSpaces code parts guarded (and not
guarded) with INCLUDE_CDS
When looking at a build configuration with cds disabled at build time.
But I'm totally fine with your answer about not using INCLUDE_CDS everywhere.
Thanks, Matthias
>Hi Matthias,
>
>We don't use INCLUDE_CDS everywhere so we can avoid cluttering the code.
>In many cases, functions called inside if (UseSharedSpaces) are declared
>to have empty bodies. E.g.,
>
>void VM_RedefineClasses::doit() {
> Thread *thread = Thread::current();
>
> if (UseSharedSpaces) {
> // Sharing is enabled so we remap the shared readonly space to
> // shared readwrite, private just in case we need to redefine
> // a shared class. We do the remap during the doit() phase of
> // the safepoint to be safer.
> if (!MetaspaceShared::remap_shared_readonly_as_readwrite()) {
> log_info(redefine, class, load)("failed to remap shared readonly
>space to readwrite, private");
> _res = JVMTI_ERROR_INTERNAL;
> return;
> }
> }
>
>class MetaspaceShared {
> static bool remap_shared_readonly_as_readwrite() NOT_CDS_RETURN_(true);
>
>
>So hopefully the C++ compile will just elide all the code inside the if
>(!...) branch (also also the check for UseSharedSpaces). There may be a
>few places where we should have added #if INCLUDE_CDS. For example,
>InstanceKlass::restore_unshareable_info.
>
>We are regularly building the minimal VM which doesn't have INCLUDE_CDS.
>So it looks like the VM will be built correctly when INCLUDE_CDS is not
>specified, but it probably has a bit of dead code.
>
>Are you mainly trying to reduce the size of libjvm when CDS is not enabled?
>
>Thanks
>- Ioi
>
>
>On 7/5/17 6:36 AM, Baesken, Matthias wrote:
>> Hello, when looking into CDS related build options, I noticed that most
>> code-parts that are executed only when UseSharedSpaces is set,
>> are guarded by the compile-time macro INCLUDE_CDS to support
>> switching off compilation of this coding
>> when CDS is disabled at compile time :
>>
>>
>> See hotspot/make/lib/JvmFeatures.gmk :
>>
>> ifneq ($(call check-jvm-feature, cds), true)
>> JVM_CFLAGS_FEATURES += -DINCLUDE_CDS=0
>>
>>
>>
>> However some places miss the compile-time guarding ( #if INCLUDE_CDS ....)
>> for example in
>>
>>
>> share/vm/prims/jvmtiRedefineClasses.cpp
>> share/vm/memory/universe.cpp
>>
>> (also some other places)
>>
>>
>> Should I prepare a change and add the compile-time guard at the places where
>> missing as well ?
>>
>> Best regards, Matthias
