RFR: 8284900: Check InitialHeapSize and container memory limits before startup [v8]

[Severin Gehwolf]

On Thu, 21 Apr 2022 11:45:55 GMT, Stefan Karlsson <stefank at openjdk.org> wrote:

>> src/hotspot/share/gc/shared/gcArguments.cpp line 147:
>> 
>>> 145:   if (OSContainer::is_containerized() && FLAG_IS_CMDLINE(InitialHeapSize)) {
>>> 146:     jlong limit = OSContainer::memory_and_swap_limit_in_bytes();
>>> 147:     if ((limit > 0) && (InitialHeapSize >= (julong) limit)) {
>> 
>> Perhaps we should generalize this to use `os::physical_memory()` here instead of the Linux-specific `OSContainer` API? `os::physical_memory()` would return the container limit if it detects so.
>
> @jerboaa Good point. Also take a look at Arguments::set_heap_size() and how that function uses os::physical_memory() and also limit_heap_by_allocatable_memory(). It seems like any change in GCArguments should go hand-in-hand with the code in set_heap_size.

> > Perhaps we should generalize this to use `os::physical_memory()` here instead of the Linux-specific `OSContainer` API? `os::physical_memory()` would return the container limit if it detects so.
> 
> What will happen with `-Xms7G` on a machine configured with 4G physical memory + 4G swap space? Does `os::physical_memory()` return `physical memory + swap space size`?

It doesn't. What would happen on a physical machine, though? It should really do the same thing regardless of the container settings. Container settings, in a nutshell, should be an abstraction of "physical" host. Otherwise behave the same. Having said that, in containers (at least kubernetes) swap is usually disabled. Also, does it make sense to allow `-Xms7g` on a system with `4G` of physical RAM? I'm doubtful.

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PR: https://git.openjdk.java.net/jdk/pull/8256