runtime: use MADV_REMOVE on Linux

[113xiaoji]

Starting with Go 1.12, the default configuration utilizes MADV_DONTNEED, but this doesn't guarantee that the operating system will immediately reclaim the memory. In containerized environments where resources are scarce and limits are set relatively low, there's still a high likelihood of running into an Out Of Memory (OOM) situation.

To address this issue, an option can be added to support MADV_REMOVE, allowing the reclaimed memory to be promptly returned to the operating system. This solution is particularly suited to scenarios that are sensitive to memory usage but not as concerned with efficiency.

For more detailed information on this subject, you can refer to the Linux man-pages: Linux man-pages.

[seankhliao]

cc @golang/runtime

[113xiaoji]

cc @golang/runtime

thank you

[ianlancetaylor]

There is no API change here so taking out of the proposal process.

[mknyszek]

I don't think MADV_REMOVE applies in this circumstance. From the man pages you linked (emphasis is mine):

The specified address range must be mapped shared and writable.

All the Go runtime's mappings for the heap are private anonymous mappings. This madvise flag seems geared specifically toward memory-mapped files.

I'm not sure if this does exactly what you want, but on Linux platforms that don't support MADV_DONTNEED or MADV_FREE, the runtime will remap the pages (not unmap, just map over them again). In any case, I think it's unlikely that we'll add a new knob to select which madvise to use. The existing GODEBUG is already kind of an accident: it was only added because switching to MADV_FREE specifically caused problems.

[mknyszek]

In triage now, I don't think this is actionable, unless I'm misunderstanding the requirements of MADV_REMOVE. Closing for now.