RFR: JDK-8318636: Add jcmd to print annotated process memory map [v6]

[Johan Sjölen]

On Sat, 28 Oct 2023 13:04:05 GMT, Thomas Stuefe <stuefe at openjdk.org> wrote:

>> Analysts and supporters often use /proc/xx/maps to make sense of the memory footprint of a process.
>> 
>> Interpreting the memory map correctly can help when used as a complement to other tools (e.g. NMT). There even exist tools out there that attempt to annotate the process memory map with JVM information.
>> 
>> That, however, can be more accurately done from within the JVM, at least for mappings originating from hotspot. After all, we can correlate the mapping information in NMT with the VMA map.
>> 
>> Example output (from a spring petstore run):
>> 
>> [example_system_map.txt](https://github.com/openjdk/jdk/files/13179054/example_system_map.txt)
>> 
>> This patch adds the VM annotations for VMAs that are *mmaped*. I also have an experimental patch that works with malloc'ed memory, but it is not ready yet for consumption and I leave that part of for now.
>
> Thomas Stuefe has updated the pull request incrementally with one additional commit since the last revision:
> 
>   fix various builds

Hi Thomas,

Did another run through. I haven't looked at `CachedNMTInformation` in depth yet.

src/hotspot/os/linux/memMapPrinter_linux.cpp line 79:

> 77: void MemMapPrinter::pd_iterate_all_mappings(MappingPrintClosure& closure) {
> 78:   FILE* f = os::fopen("/proc/self/maps", "r");
> 79:   if (f != nullptr) {

Suggestion: `if (f == nullptr) return;`, reduces indentation for main body of code.

src/hotspot/os/linux/memMapPrinter_linux.cpp line 80:

> 78:   FILE* f = os::fopen("/proc/self/maps", "r");
> 79:   if (f != nullptr) {
> 80:     static constexpr size_t linesize = sizeof(ProcMapsInfo);

Make this `constexpr const`, remove `static`.

src/hotspot/os/linux/memMapPrinter_linux.cpp line 82:

> 80:     static constexpr size_t linesize = sizeof(ProcMapsInfo);
> 81:     char line[linesize];
> 82:     while(fgets(line, sizeof(line), f) == line) {

Style: space between `while` and `(`.

test/hotspot/jtreg/serviceability/dcmd/vm/SystemMapTest.java line 3:

> 1: /*
> 2:  * Copyright (c) 2023, Oracle and/or its affiliates. All rights reserved.
> 3:  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.

Copyright Redhat

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PR Review: https://git.openjdk.org/jdk/pull/16301#pullrequestreview-1703761626
PR Review Comment: https://git.openjdk.org/jdk/pull/16301#discussion_r1375986785
PR Review Comment: https://git.openjdk.org/jdk/pull/16301#discussion_r1375988375
PR Review Comment: https://git.openjdk.org/jdk/pull/16301#discussion_r1375987037
PR Review Comment: https://git.openjdk.org/jdk/pull/16301#discussion_r1375994689