RFR: 8280289: Enhance debug pp() command with NMT info [v3]

[Thomas Stuefe]

On Fri, 21 Jan 2022 17:22:12 GMT, Zhengyu Gu <zgu at openjdk.org> wrote:

>> JDK-8275320 enhanced NMT malloc header, provided ability to identify if a pointer points to a malloc'd memory. Further,  JDK-8277822 enabled NMT for debug builds.
>> 
>> This is a good opportunity to integrate NMT to debug pp() command to provide useful information collected by NMT. 
>> 
>> For example:
>> 
>> NMT=summary
>> 
>> (gdb) call pp(0x7f2d9803db70)
>> "Executing pp"
>> 0x00007f2d9803db70 malloc'd 1576 bytes by Internal
>> 
>> (gdb) call pp(0x00007f4300a20000)
>> "Executing pp"
>> 0x00007f4300a20000 in mmap'd memory region [0x00007f4300a20000 - 0x00007f4310000000] by GC
>> 
>> 
>> NMT=detail
>> 
>> 
>> (gdb) call pp(0x7f2d9803db70)
>> "Executing pp"
>> 0x00007f2d9803db70 malloc'd 1576 bytes by Internal
>> [0x00007f2d9f1b784b] G1Arguments::create_heap()+0x1b
>> [0x00007f2d9f98a855] universe_init()+0x85
>> [0x00007f2d9f2e0a97] init_globals()+0x37
>> [0x00007f2d9f960acb] Threads::create_vm(JavaVMInitArgs*, bool*)+0x3db
>> 
>> (gdb) call pp(0x00007f4300a20000)
>> "Executing pp"
>> 0x00007f4300a20000 in mmap'd memory region [0x00007f4300a20000 - 0x00007f4310000000] by GC
>> [0x00007f433dc49c7f] reserve_memory(char*, unsigned long, unsigned long, int, bool)+0x17f
>> [0x00007f433dc4cf0b] ReservedSpace::reserve(unsigned long, unsigned long, unsigned long, char*, bool)+0x14b
>> [0x00007f433dc4d527] ReservedSpace::initialize(unsigned long, unsigned long, unsigned long, char*, bool)+0x1c7
>> [0x00007f433d949d40] ShenandoahHeap::initialize()+0x340
>
> Zhengyu Gu has updated the pull request incrementally with one additional commit since the last revision:
> 
>   Missing include file

Some small remaining nitpicks.

src/hotspot/share/services/virtualMemoryTracker.cpp line 683:

> 681: 
> 682:   bool do_allocation_site(const ReservedMemoryRegion* rgn) {
> 683:     if (_p >= rgn->base() && _p < rgn->base() + rgn->size()) {

Use `VirtualMemoryRegion::contain_address()`?

src/hotspot/share/services/virtualMemoryTracker.cpp line 693:

> 691: };
> 692: 
> 693: const ReservedMemoryRegion* VirtualMemoryTracker::find_region(void* p) {

Curious, is this thread-safe? Do we care if not?

src/hotspot/share/utilities/debug.cpp line 496:

> 494:           p2i(p), p2i(rgn->base()), p2i(rgn->base() + rgn->size()), rgn->flag_name());
> 495:         if (tracking_level == NMT_detail) {
> 496:           rgn->call_stack()->print_on(tty);

Idea for later cleanup. In detail mode, malloc headers have no call stack (NULL) whereas regions have an empty stack (NativeCallStack::_empty_stack) ? If yes, may be nice to unify this behavior. 

Maybe also remove checks like this here, for MemTracker::tracking_level=detail, in favor of checking if rgn->call_stack() is NULL. That would feel more consistent and allow us (if we ever wanted) to have regions with and without stack.

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PR: https://git.openjdk.java.net/jdk/pull/7160